Passive House Plus (Sustainable building) issue 35 UK

INSULATION | AIRTIGHTNESS | BUILDING SCIENCE | VENTILATION | GREEN MATERIALS

S U S TA I N A B L E B U I L D I N G

PECKING ORDER

Award-winning passive house makes mark on the South Downs

Study shows lower lung cancer risk in passive houses Highland warrior

Easter Ross passive house goes all in on timber

Zero in Inspired Dublin home offers net zero energy living model

Build back better?

Will government stimulus lead to quality retrofits?

Issue 35 £5.95 UK EDITION

RADON REDUCTIONS

SAME HOUSE, DIFFERENT HOME.

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EDITOR’S LETTER

editor’s letter W

e have been living through extraordinary times, and the next few months are set to be no different.

When I sit down to write the editor’s letter for our next issue, the next US presidential election will have taken place, hopefully leading to a peaceful, democratic, conclusion culminating in the end of the reign of a man who has done so much damage to the world in such a short time.

We will be closer to a conclusion on the Brexit saga, hopefully delivered in a way which doesn’t threaten the peace, stability and prosperity of Ireland and the UK. We will also be heading decisively into winter, and I hope with every fibre in my being that a time of year when people tend to stay indoors, close windows and reduce ventilation doesn’t contribute to a significant spike in Covid-19 cases.

If the authorities had been quicker to accept the growing weight of evidence on the airborne path as not only a significant but perhaps the most significant route for transmission of Covid, we could have been so much better prepared, and our chances of avoiding a dreadful winter may have been substantially better. That’s not to say that airborne spread is the only issue, or that accepting its significance would lead to its eradication. We’re faced with a fiendishly complex problem, and solving it requires us to make lots of changes in how we live in our day to day lives.

So, ventilation is important, but if we place too much emphasis on it, it could give us false

ISSUE 35 confidence. That includes everything from social distancing, to spending less time mixing with people from outside our households, to wearing masks, to being hypersensitive to activities that may significantly increase aerosols, and many more considerations besides. But caveats like this side, it’s becoming increasingly clear that ventilation is a critical tool that we must use to tackle Covid, and with much higher ventilation rates than we would normally advocate in buildings where people are congregating.

Hopefully in the process we’ll start to collectively gain an appreciation of the health, wellbeing and productivity benefits that good ventilation brings. In the longer term, this should give us pause to reflect on how to ensure our new build and retrofit efforts help to give us resilience in a world where pandemics may linger on, or where another pandemic may be around the corner.

It’s one thing to justify colder indoor temperatures and higher heat energy use over this winter given the exceptional circumstances we face. But neither our pockets nor the planet can afford this to become part of the new normal. We must learn from these circumstances and prepare ourselves so that our buildings don’t threaten our health, but instead protect it, and help us to adapt to whatever adverse circumstances the future may throw at us.

Regards, The editor

Contributors

Toby Cambray Greengauge Building Energy Consultants Marc Ó Riain doctor of architecture Peter Rickaby energy & sustainability consultant David W Smith journalist

Print

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Cover

Hill House passive house, South Downs NP Photo by Charles Meloy

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Disclaimer: The opinions expressed in Passive House Plus are those of the authors and do not necessarily reflect the views of the publishers.

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About

Passive House Plus is an official partner magazine of The Association for Environment Conscious Building, The International Passive House Assocation and The Passivhaus Trust.

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CONTENTS

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CONTENTS COVER STORY

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INTERNATIONAL

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NEWS

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This issue features a new block of passive house apartments in north-west Spain.

World’s first passive hospital nears certification, no insulation without ventilation in new retrofit grant scheme, and experts call for use of CO2 sensors in fight against Covid.

COMMENT Returning to his regular series on the evolution of sustainable building during the 20th century, Dr Marc Ă“ Riain takes look at the first serious attempt to build a house with net zero energy use; and Dr Peter Rickaby writes about domestic retrofit in the wake of Covid, and the importance of doing it right.

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CASE STUDIES

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Pecking order Award-winning passive house makes an elegant mark on the South Downs

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In 2016, builder David Lane decided to buy a large 1950s house in Cork city and undertake a tricky deep retrofit, turning the run-down property into an upmarket passive house. It’s about as far from the traditional model of property development as you can imagine — but it holds some crucial lessons for what we do with our urban buildings in the era of climate breakdown.

INSIGHT Radon

Radon is one of the most dangerous indoor air pollutants, yet there is little research on how it is affected by different forms of construction and ventilation. A new study, however, suggests that homes built to the passive house standard are significantly less at risk of radon build-up.

Despite the challenges of getting planning permission within a national park, a new passive house on a hillside in the South Downs managed to woo the planners with a sympathetic, discerning design inspired by a surprising source — two dilapidated old chicken sheds.

Speculative effort Extraordinary A1 Cork upgrade is Ireland’s first developer led Enerphit

Zero in Inspired design offers route to net zero energy living

It sounds like an impossibility: a high density, architectural, zero energy home on the tightest of back garden sites, adaptable to the needs of everyone from empty nesters to a family of six without opening a toolbox. But sometimes a project comes along that redefines what is possible.

Highland warrior Scottish passive house built with innovative local timber system

A beautifully detailed and rustic new passive house in the north of Scotland was built with a unique offsite construction system using local timber, and was created by a design-and-build firm that aims to put sustainability at the heart of everything it does.

CONTENTS

63

MARKETPLACE Keep up with the latest developments from some of the leading companies in sustainable building, including new product innovations, project updates and more.

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The condensation myth

Condensation within the structure of buildings is a lot more complex than condensation in a sweaty pub on a Friday night, writes building physics expert Toby Cambray.

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INTERNATIONAL PAS S I V E & EC O B UIL D S F R OM A R OU ND THE WO R L D

IN BRIEF Building: Seven-storey apartment block Location: Vigo, Galicia Building method: Externally insulated clay block with concrete frame Standard: Passive house classic certified

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I N T E R N AT I O N A L

S PA I N

VIGO, GALICIA, SPAIN

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Photos: Carlos Prieto

striking new block of passive house apartments has risen in the city of Vigo, in north-west Spain, on the site of a popular old hotel.

But the team behind the project, led by architect Leonardo Llamas Álvarez of Edifico Arquitectura, faced a daunting challenge: preserving the concrete slabs and columns from the original Hotel Galicia while building an airtight and superinsulated structure on the narrow urban site, between two existing party walls.

The new walls were built from clay blocks, insulated externally with mineral wool, with new triple glazed passive house certified windows installed too. A gypsum plaster coat on the inside of the new walls provides the primary layer of airtightness.

Where it faces the street, the building has a ventilated façade finished with granite, and an external lattice of pine slats for shading.

The finished building has one large apartment per floor. Inside, the feel of the building is defined by the wood and concrete finishes, particularly in the circulation spaces. Cross-laminated timber from Norway spruce was used for the construction of the entrance stairs, including a first step which appears to be floating in thin air.

Meanwhile four air source heat pumps supply an underfloor heating and cooling system in each apartment.

And while the project’s developer was initially afraid that building to the passive house standard might compromise the aesthetics of the project, he is reportedly delighted with the end result — particularly with the indoor air quality. The building’s mechanical ventilation with heat recovery systems also helps to reduce the build-up of radon gas, for which Vigo is in a highrisk area.

Overall, achieving the full passive house standard while preserving some of the original hotel’s structure represents a remarkable achievement on such a difficult site.

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WANT TO KNOW MORE? The digital version of this magazine includes access to exclusive galleries of architectural drawings.

The digital magazine is available to subscribers on www.passive.ie

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Eco-friendly refrigerant R32

NEWS

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NEWS World’s first passive hospital nears certification

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he world’s first passive house hospital, currently being built in Frankfurt, is a step closer to certification, after the 78,000 square metre building passed its airtightness test with flying colours.

The Passive House Institute in Darmstadt has been consulting on the project right from the start, having first prepared an in-depth study on how the passive house standard can be applied to hospitals.

The institute has now been tasked with certifying the project.

The building’s airtightness test confirmed that it achieves a value of 0.13 air changes per hour at 50 Pascals, well inside the passive house standard of 0.6.

Oliver Kah of the Passive House Institute was present on-site during the pressure test. "The test in the eight-storey building went very well. The new build is outstandingly airtight, and is now a little closer to certification,” he said.

Kah also praised the construction team, as well as the airtightness testers. One thousand windows had to be closed for the test, and the dampers of more than 50 units connected to the ventilation and air conditioning system checked. Other technical systems also had to be tested, including numerous elevators whose motorised dampers have to open towards the outside in case of fire.

"The prior inspection of the more than 2,000 rooms alone was a huge task. However, because everything was well-prepared, the test for the entire new build could be completed in a single day,” said Kah. Scaffolding has now been dismantled and interior finishing is being completed. The costs for the building are estimated at around €263 million. Two existing hospital buildings dating back to the 1960s will be demolished after the passive house hospital opens. • (above) The world’s first passive house hospital, in Frankfurt, is nearing completion.

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No insulation without ventilation in Green Homes Grant scheme - TrustMark

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entilation will be an essential requirement of insulation retrofits under the UK government’s new £1.5 billion Green Homes Grant voucher scheme, Passive House Plus can reveal.

The message comes from Phil Mason, head of regulatory engagement at TrustMark, the government endorsed quality scheme that tradespeople must be registered with in order to work on Green Homes Grant-funded projects.

Mason said: “We’re taking the approach – and I dare say you’ve heard Peter Rickaby say this on a number of occasions – no insulation without ventilation. What that’s doing is giving more and more assurance that we’re moving completely in the right direction.” Rickaby, who writes a column for Passive House Plus, has been a prominent figure in the development of retrofit standards in the UK. Mason added that TrustMark has also worked hard to ensure the compliance elements of the scheme are within the organisation’s delivery mandate. Compliance checks will be carried out by the licenced scheme providers, in conjunction with TrustMark’s internal desktop audit processes and field-based surveyors to physically inspect the work.

While the percentages of onsite audits are still being agreed, Mason said it would be at a “robust risk-based level”.

Under the new scheme, installers must be certified to either PAS 2030:2017 or to PAS 2030:2019, but new entrants can only be certified to PAS 2030:2019. Mason said that TrustMark will require installers to ensure ventilation provisions meet the requirements set out in PAS 2030:2017, at a minimum, with all relevant TrustMark registered businesses moving to full PAS 2035 delivery after June next year.

Work under the scheme must comply with PAS 2030:2017 at a minimum, with transitional arrangements bringing requirements from PAS 2030:2019 and PAS 2035:2019 in too. However, the installer may opt to comply with PAS 2030:2019 and PAS 2035:2019 where they have the relevant certification and processes in place. All measures installed in park homes, high-rise buildings and buildings that are both traditionally constructed and protected must be delivered by a PAS 2030:2019 certificated installer and in compliance with PAS 2030:2019 and PAS 2035:2019.

These rules have been applied because the PAS 2035:2019 supply chains have not yet matured enough in terms of volume for this standard to be applied to all projects delivered under the scheme, but it’s believed there is sufficient capacity to cover projects of significant risk, and the supply chain – including the availability of retrofit coordinator services – continues to grow.

PAS 2030:2017 contains requirements for designs, and for dealing with interactions between measures, including construction details, compatible specifications, managing thermal bridges, eliminating thermal bypass, etc., and for ventilation upgrades. Similarly, all-encompassing requirements are included in PAS 2035, albeit with more stringent obligations.

TrustMark is incorporating PAS 2035:2019/PAS 2030:2019 through the underlying published transitional arrangements as agreed with BSI, BEIS, Ofgem and UKAS. These will expire on 30 June 2021. Therefore, the expectation is that all ‘in scope work’ delivered by TrustMark registered businesses after that date will be completed by appropriately certified businesses and in compliance with those standards. •

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NEWS

Experts call for CO2 sensors as tool in Covid fight C O2 levels in rooms and other enclosed spaces should be used as a proxy for Covid transmission risk, a number of leading experts have said, as the evidence increasingly points towards airborne transmission being a major factor in the spread of the virus.

“Since the coronavirus is spread through the air, higher CO2 levels in a room likely mean there is a higher chance of transmission if an infected person is inside,” leading aerosol scientist Prof Shelly Miller writes in The Conversation.

“Simply put, the more fresh, outside air inside a building, the better. Bringing in this air dilutes any contaminant in a building, whether a virus or a something else, and reduces the exposure of anyone inside.”

Miller cites a 2019 study on a tuberculosis outbreak in Taipei University, Taiwan, where many rooms were poorly ventilated and reached CO2 levels above 3,000 parts per million (ppm).

When engineers brought levels down to under 600 ppm the outbreak stopped. “According to the research, the increase in ventilation was responsible for 97% of the decrease in transmission,” said Miller, before going on to recommend a CO2 target of 600 ppm.

Meanwhile REHVA, the Federation of European Heating, Ventilation and Air Conditioning Associations has called for the installation in school classrooms of CO2 monitors with traffic-light indicators, “at least in schools where ventilation depends on opening windows and / or grids”.

Prof John Wenger, director of the Centre for Research into Atmospheric Chemistry in University College Cork suggests a target of 1,000 ppm if CO2 is being used as a proxy for Covid in classrooms, and argues that room level transmission is “the key. It’s in the air, and it can fill a room. The amount of the virus in the air can accumulate, and we get an increased exposure. If you’re indoors, in a poorly ventilated room for a long time, then you’re at quite a high risk even if you’re distanced, because the air moves around.”

A new study by leading aerosol scientists Zhe Peng and Jose L Jimenez, titled ‘Exhaled CO2 as Covid-19 risk proxy for different indoor environments and activities’, has found that indoor CO2 measurements by low-cost sensors hold promise for mass monitoring of indoor aerosol transmission risk for Covid-19 and other respiratory diseases, but that different CO2 level targets should be set based on the environment and activity type.

The study – published as a pre-print in September – explains that target CO2 levels for a given infection risk level can vary by a factor of 100 or more depending on the situation and activity type. This is because the risk is subject to factors such as the number of infected people in a region, and the fact certain measures such as mask wearing or air filtration may reduce presence of the airborne virus without reducing CO2 levels. As Jimenez points out, certain activities increase virus emission far more than CO2 levels, such as talking, singing and shouting.

“The stronger vocalization, the higher risk, and the more intense activity, the higher risk,” the study says. Jimenez nonetheless argues that using CO2 levels to monitor infection risk is a “very good idea”, because infected people exhale CO2 and Covid as they breathe, talk etc., and as both CO2 and the virus are removed by ventilation with outdoor air. •

T

he Walled Garden passive house in Devon, designed by McLean Quinlan Architects, has been nominated in the rural house category of the 2020 Dezeen Awards public vote. The annual Dezeen Awards, run by leading design website Dezeen.com, celebrate the world’s best architecture, interiors and design.

Built with structural insulated panels, the Walled Garden secured planning permission under the paragraph 55 ‘exceptional design’ clause of the National Planning Policy Framework (since changed to paragraph 79). In its first year in operation, almost two-thirds of the 7.5 MWh of energy consumed by this certified passive house was produced by the onsite solar photovoltaic array.

Voting for the Dezeen Awards public vote remains open until 12 October on Dezeen.com.

Photos by Jim Stephenson

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NEWS

NHS to get its first passive building

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he NHS has given the go ahead for its first passive house building. The new Foleshill health centre in Coventry is designed by Tooley & Foster Partnership. Patients and doctors at Foleshill are currently using a temporary building situated in a carpark.

Detailed life cycle costing shows that this passive house building will save the NHS nearly £1m in running costs over the 25 years after construction, according to the architects.

The development is expected to cost £3.3m and will be constructed using an offsite modular system from Portakabin.

The project is a partnership between

Community Health Partnerships (CHP), NHS Coventry, and Coventry & Rugby Clinical Commissioning Group (CCG).

The building will be certified to BREEAM Excellent and heated with an air source heat pump. There will be also charging points for electric cars, secure cycle parking, and a solar photovoltaic array.

Designed to meet the needs of an expected 10,000 local patients, Tooley & Foster state that the facility will maximise natural light and boast an attractive timber and render exterior.

“The building’s strong identifiable frontage provides visitors with a sense of arrival while being respectful towards its

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surroundings,” the architects state.

The building will feature five consulting rooms, two treatment rooms and ancillary accommodation including waiting and reception areas.

“This is a very exciting project which has taken a huge amount of effort to bring to a conclusion,” said CHP’s chief commercial officer, Malcolm Twite. He added that the building would make a contribution towards reducing the carbon footprint of England’s healthcare sector, estimated to be 4-5% of national emissions. • (above) An artist’s rendering of the new passive Foleshill health centre.

COLUMN

DR PETER RICKABY

Will we really build back better?

As governments rush to jump-start their economies, there is a danger that important lessons for how to retrofit homes will be lost in the rush to build. But there is a better way, writes Dr Peter Rickaby.

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wrote in my last column about how lockdown provided a glimpse of a more sustainable future. I also predicted a battle between those who want to put everything back exactly as it was, and those who want us to learn lessons for sustainability.

We are now in the battle of the three Bs: for bankers, business bosses and politicians it’s ‘build, build, build’, but for others it’s ‘build back better’. In between there are a lot of people who just want their jobs and social lives back.

In recent weeks I have participated in many meetings, on both sides of the Irish Sea, about how we might use domestic retrofit to create jobs while simultaneously reducing emissions. After more than twenty years promoting domestic retrofit as an essential element of sustainability, with barely a flicker of response in Whitehall and little enthusiasm elsewhere, now everyone wants it yesterday! It’s like waiting for the number two bus in Milton Keynes (which I did often, before lockdown): I stand at the stop for an hour, then three buses come along at once.

In the UK, we have spent ten years and at least £20 million learning how to do domestic retrofit well: how to identify and manage risks, how to eliminate the performance gap and how to protect the buildings and the health and wellbeing of occupants.

Thousands of people have contributed, starting with the Retrofit for the Future and Scaling Up Retrofit competitions, then the

but not much about how to do it at scale. If we are to retrofit nearly thirty million homes, well-managed processes are going to be as important as good designs and specifications.

Imagine how exhilaration turned to horror when I learned first that the UK Government has allocated £1.5 billion to creating jobs for unemployed workers by insulating between 150,000 and 600,000 homes by March 2021, and then that the industry is lobbying to relax or abandon the quality assurance framework for the sake of speed and profit.

As I write, the argument goes on. By the time this is published we will probably know how it turned out, but if ministers give in to the temptation to dilute hard-won standards then it will be down to them when it goes wrong for householders.

What is disappointing about this episode is that even after throwing nearly £3 million into improving standards and managing risks, some people in the UK government still seem to think that retrofit is an easy process that they can use to create jobs simply by throwing money at it. In reality, retrofit is complex and risky, and they are gambling with people's homes and lives.

We are told that there may be more to come for retrofit in 2021, on a larger scale. Many friends and colleagues in the UK and Ireland are now working on proposals for national domestic retrofit programmes, and they are including the latest standards. Two interesting ideas have emerged from this work.

The idea is simple: lead with ventilation, before improving the fabric.

Green Deal Communities programme, followed by the Each Home Counts review, the establishment of the TrustMark quality assurance framework and the retrofit standard PAS 2035, and recently the retrofit supply chain pilots and the government’s whole house retrofit competition. In Ireland, the deep retrofit pilots also taught us a lot.

Along the way we have had some disasters: in Glasgow, Edinburgh and Preston, at Grenfell Tower, and in thousands of homes ruined by inappropriate or poorly installed insulation. All this work, money and misery have taught us how to deliver good retrofit,

The first idea springs from the lack of skilled capacity in the retrofit industry, and the need to allow time for training before we deliver at scale. The point is that the quality of retrofit reflects the quality of the original assessment of the dwelling. The idea is to separate assessment from the rest of the process and deliver free or subsidised whole-dwelling assessments, improvement option evaluations and retrofit plans. These assessments, running ahead of retrofit itself, would engage households, provide knowledge of the stock, establish a pipeline of work to encourage investment and

finance, and allow time for retrofitters to be trained.

The second idea springs from two maxims: ‘fabric first’ and ‘no insulation without ventilation’. Improving the building fabric, to reduce demand, before moving on to decarbonise and improve the efficiency of building services, has always made sense. Now, with so many uncertainties about 2050 (will the electricity grid be completely decarbonised? will we have affordable batteries? how far will low-carbon heat networks penetrate?) fabric first makes even more sense – but not without ventilation.

It is essential when insulating to replace lost infiltration and ensure good indoor air quality by improving ventilation. In the age of Covid, ventilation looks even more important. Effective ventilation also deals with the condensation, damp and mould (CDM) problems that many homes suffer from, which insulation alone will not fix.

So the idea is simple: lead with ventilation, before improving the fabric; make homes safer for installers and deliver immediate improvement by eliminating CDM first.

This approach was successful at Thamesmead in south-east London, the Northern Ireland Housing Executive is trying it in homes outside Derry, and the same approach is about to be applied to several hundred mouldy flats in south London.

Domestic retrofit has a long way to go, and we may have more disasters, but in the UK we now have the quality assurance framework and technical standards to avert them. Insisting that those standards are applied will help to improve our housing and protect the health and well-being of residents. n

Dr Peter Rickaby is an independent energy and sustainability consultant.

He helps to run the UK Centre for Moisture in Buildings at University College London, chairs the BSI Retrofit Standards Task Group, and is active in training building professionals in retrofit coordination and risk management.

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COLUMN

MARC Ó RIAIN

The world’s first ‘zero energy’ house Returning to his regular series on the evolution of sustainable building during the 20th century, Dr Marc Ó Riain takes look at the first serious attempt to build a house with net zero energy use.

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uring the 1973-74 oil crisis Denmark, which was massively impacted by the quadrupling of energy prices, invested in applied energy conservation in building research. The NATO sponsored Lyngby ‘dth-nul-energihus/zero-energy-house’ near Copenhagen would be the world’s first attempt to create a measured ‘zero energy house’ (as calculated against space heating and domestic hot water demand). The Solar Energy Pilot Study (1973-78) zero energy house team was led by Professor Vagn Korsgaard from the Technical University of Denmark.

The design involved two habitable structures (60 m2 each) linked by a glazed atrium (70 m2) which functioned as an unheated wintergarden. This was one residence, occupied and monitored for a year. Understanding that heat loss would drive heating demand the team opted to maximise energy conservation primarily through passive means, such as by envelope insulation and airtightness, augmented by passive solar heat gain, and heat emitted from internal loads like people and appliances. Augmenting this passive approach was the use of flat plate water-based solar collectors connected to a heavily insulated seasonal heat storage tank.

What is surprising about this project is the standards of insulation and airtightness it achieved. Understanding the impact of infiltration on heat loss, the team opted to build the

We stand on the shoulders of such pioneers. structure with prefabricated sandwich panels insulated with mineral wool, to minimise field joints. The U-values were 0.14 for walls (300 mm insulation) and 0.10 for the floors and ceiling (400 mm insulation). There were also double glazed windows (U-value: 3.0) with night time insulated external shutters that targeted a U-value of 0.5 (but achieved 0.9 in practice due to thermal bridging).

The team understood the need to weather-strip the windows to the panel walls and seal electrical conduits, resulting in an estimated 3 m3/hr/m2 airtightness at 50 Pascals. The mechanical heat recovery ventilation system then delivered 0.7 air changes per hour working at 70% efficiency.

Each room had a TRV controlled fan coil unit with air passing over hot water pipes coming

The Danish 'zero energy house', built in the aftermath of 1973-74 oil crisis.

from a 400 litre hot water tank, located in the 300 m3 seasonal storage tank (a tricky location to service). Run off from showers fed into the tank inlet, recovering only 20% of heat energy.

An auxiliary electric 4 kW hot water heating system provided a backup.

The main solar water array was a vertically mounted collector with black painted tubular radiator bars filled with water within a glass box, and insulated at the back. Water had to be drained from the system to protect against frost, and the glass actually fractured in its metal frame, breaking 20% of the array one February morning in 1976 due to the thermal differential.

I found it surprising, given the existing published experiments with Solar 1 in MIT in the 1930s and the issues with the Dover Sun house in the early 1950s, that the researchers elected to go with water which would freeze, and glass which was prone to crack with heat differentials.

The team ran the ‘Zero Energy House’ for a reference year with a calculated performance, and then ran it occupied by a family for a year as a measured performance. The occupants didn’t always close doors or windows, and sometimes forgot to close the exterior shutters, therefore space heat demand (SHD) was higher but strangely domestic hot water demand was much lower during the occupied year. The desktop estimation for SHD was 2,300 kWh/yr but the actual occupied SHD was 5,800 kWh/yr.

The seasonal storage tank lost about 40% of its energy through transmission, and while the solar collectors worked quite well,

generation and thermal storage ran 20% behind calculations with less solar incident in the occupied year versus the previous reference year. For the occupied year solar thermal only covered 43% of the total space heat demand (5,800 kWh) and 27% (1,000 kWh) of the hot water load (2,700 kWh). The auxiliary electrical space heating and ventilation was 5,000 kWh. So in a real world test the ‘zero energy building’ did not achieve a net zero balance, it only achieved 55% of its target, but that was a critical first step towards zero energy buildings.

The team used super-insulation, recognised thermal bridging, achieved good airtightness and used heat recovery ventilation. The complicated active systems like solar water and seasonal storage tank were prone to damage and efficiency issues, and were extremely expensive. However, they pointed the way for the rest of us and we stand on the shoulders of such pioneers whose legacy we are only seeing in mainstream construction today. n

Dr Marc Ó Riain is a lecturer at the Department of Architecture at Cork Institute of Technology, one of the founding editors of Iterations design research journal and practice review, a former president of the Institute of Designers in Ireland, and has completed a PhD in low energy building retrofit, realising Ireland’s first commercial NZEB retrofit in 2013.

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SCOTLAND

CASE STUDY

ENERGY BILLS

£35

PER MONTH AVERAGE BILL FOR ALL ENERGY Building: 137 m2 fully prefabricated timber frame dwelling Site: Strathpeffer village, Easter Ross Standard: Passive house classic

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CASE STUDY

SCOTLAND

STUDY

STORE

COVERED DECK

LIVING ROOM

SECTION

HIGHLAND WARRIOR STUDY

STORE

COVERED DECK

LIVING ROOM

SECTION

STORE

STORE

PLANT

SCOTTISH PASSIVE HOUSE BUILT WITH INNOVATIVE LOCAL TIMBER SYSTEM BATHROOM

STUDY

UP

UP

MASTER BED

STUDY

A beautifully detailed and rustic new passive house in the north of Scotland was built with a unique off-site construction system using local timber, and was created by a design-and-build firm that aims to put sustainability at the heart of everything it does.

STORE

STORE

STORE

VOID

PLANT

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Words by John Cradden

UPPER FLOOR PLAN

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PLANT WORKSHOP BATHROOM

WORKSHOP WOOD LOG STORAGE

UP

STUDY

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GEANAISEAN HOUSE STRATHPEFFER

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ph+ | scotland case study | 19 SHOWER

UTILITY

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SCOTLAND

CASE STUDY

If you’ve been out on a Scottish site in the middle of winter, you really begin to appreciate how important is to have a facility that is well lit and heated.

I

f you wanted to build a house to the passive house standard but with the strongest possible nod to sustainability, timber frame construction would probably rank high on the shortlist of build methods.

But what if you were concerned about the sustainability and carbon footprint of imported timber? That’s the predicament that Tim Dawson of Strathpeffer in Scotland found himself in after receiving inheritance from his late father in 2015, enabling him to fulfil a dream of building a new home.

After a long search, he had found a local site with full planning permission for the replacement of a derelict bungalow. It also came with planning permission in principle for a second dwelling, but he liked the site so much he bought it in 2018 with the firm intention of building only one house on it.

20 | passivehouseplus.co.uk | issue 35

His other firm intention was in relation to the brief for his new ‘forever’ home. He wanted a modest, two-bed dwelling with generous office space, a utility room and adjoining workshop, and built to fully certified passive house standard but with the lowest possible carbon footprint, and constructed with local timber.

One of the two local architects that Tim consulted during his research was a unique design and build firm in Inverness called Makar. Tim felt that Makar founder Neil Sutherland was very much on his wavelength, despite the fact that the firm had never previously built a passive house (though they had designed a community centre in nearby Gairloch that is passive house certified).

Tim was particularly impressed with the standard Makar system, an off-site,

timber-based panel system very similar to a SIPS (structurally insulated panel system).

SIPS is essentially insulated timber panels assembled together, often without the need for separate structural elements, but a typical build-up is likely to have its fair share of synthetic materials like adhesives, timber preservatives and polyurethane foam insulation.

But Makar describes its unique system as ‘n-SIPS’ because of its use of all natural materials, including untreated timber, Warmcel cellulose insulation (made of recycled newspaper) and wood fibre board (made from timber waste).

The timber used for the frame is untreated Scottish-grown spruce, while Scottish-grown larch or Douglas fir is the choice for the cladding and post-and-beams. Although

CASE STUDY

SCOTLAND

their system didn’t initially meet the passive house standard, Sutherland and his architect colleague, Catriona Kinghorn, were keen to take up the challenge of designing and building a passive house as they felt confident it only needed minor amendments to meet the standard. But given its northerly highland location, it was necessary to achieve even more onerous U-values than normal for a UK passive house.

Kinghorn had qualified as a passive house designer a year before she and Sutherland met Tim. “And, actually, at the time we met Tim,” recalls Kinghorn, “I was due to be away that summer in Japan and New England visiting other passive house designers — I had a travel grant awarded by the Winston Churchill Memorial Trust — so this was always on our mind. And I guess Tim really appeared at a very fortuitous moment for the company, because it was a real meeting of minds.

“Tim’s brief was very clear. It was a really well written brief. He didn’t try to design the house itself, but he was clear on what he wanted and he didn’t want. And he really understood passive house principles; he’d made the effort, he had the technical understanding of passive house to understand why it was supported and he’d made that decision. He wanted to reach that standard.”

The site also lent itself well to passive house design, as it was well orientated with a good southerly aspect, slightly sloping downhill, with deciduous trees to the east and an area of high ground to the west — perfect for low sun shading.

It’s clear that part of the meeting of minds that Kinghorn describes is Tim’s attraction to the Makar commitment to deliver buildings that are healthy and sustainable, while also attaining his prized goal of a certified passive house.

“Passive house is an energy-balance calculation, with no comment on how the energy balance is achieved,” says Kinghorn.

“We would not have been comfortable delivering a passive house project relying solely on materials we felt are harmful to the user or the environment.”

The solution was the Makar standard Warmcel-insulated timber frame but boosted with a 180 mm (compared to the normal 60 to 80 mm) outer layer of tongue-andgroove wood fibre insulation board. Careful detailing at junctions ensured a continuous insulation jacket. The result is a ‘breathing’ wall construction, which allows moisture vapour to dissipate naturally through the wall. All timber is untreated, while an 18 mm OSB board was used as an internal airtight layer, and taped at all junctions.

“We worked really hard to reduce the timber content of the panels as much as possible [to allow more space for insulation], and to develop standard off-site panel joints that maintain the thermal envelope,” says Kinghorn. She adds that they plan eventually to use Scottish-timber-produced wood

Photography: Catriona Kinghorn / Makar

ph+ | scotland case study | 21

SCOTLAND

CASE STUDY

CONSTRUCTION IN PROGRESS

1

2

3

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5

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7

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The Makar prefabricated timber frame system being built in their workshop, showing 1 the frame, 2 the postbase, 3 the roof panel, and 4 the cladding; 5 & 6 assembly of the frame on-site; 7 the panels are built complete with insulation, doors, windows, roof and cladding; 8 18 mm OSB board was used as an internal airtight layer, and taped at all junctions; 9 the walls are finished inside with plasterboard enclosing a woodfibre-insulated service cavity.

22 | passivehouseplus.co.uk | issue 35

CASE STUDY

SCOTLAND

The final result is a lovely, understated home that really blends well into its environment.

fibre products in order to reduce reliance on insulation materials imported from abroad.

Interestingly, all Makar-built houses today are specified with MVHR (mechanical ventilation with heat recovery) but Kinghorn points out that even 10 to 15 years ago the build-up of moisture was far less of an issue with its breathable walls than other modern build methods. “Once you get to a certain level of airtightness, like passive level airtightness, you do need the MVHR ventilation,” she says. “So that goes into all of our houses as standard anyway.”

Underlying Makar’s commitment to a wide-ranging sustainable rural economy in the Highlands is that as well as tying in interests in forestry, regeneration, timber use and healthy construction and design, Neil Sutherland’s family also run an organic farm on the same site as the company’s factory.

Needless to say, being able to build its wall panels off-site conferred several advantages in meeting the challenge of building Tim’s passive house, not least a high degree of quality control.

“Our drive is to do things off-site as much as possible, simply because when you’ve been out on a Scottish site in the middle of winter, you really begin to appreciate how important is to have a facility that is well lit and heated, and everyone’s working on benches, tables and the panels are laid horizontal.”

Kinghorn also appreciates the convenience of working right next door to the factory. “As a designer, especially as a passive house designer, working literally yards away from the person building wall panels means you can literally come out and talk through problems, solve them there and then and you don’t need to wait a week while someone gets out to the site.”

The panels, which are built complete with insulation, doors, windows, roof and cladding, are typically 2.4 to three metres wide by 4.8 metres high, and weighing one to 1.5 tonnes. House superstructures are assembled on site by a small team using a 40 or 55 tonne crane, and are usually made wind and watertight in less than a week – another advantage when building in remote rural locations.

In a bid to keep its use of concrete to a minimum, the company also usually specifies pier foundations on three-metre

ph+ | scotland case study | 23

SCOTLAND

CASE STUDY

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FAN • • •

•

Highly efficient EC backward curved radial fan Constant flow fan Ultra precise and fast flow measurement done by VaneAnemometer Spare part contains complete fan (easily replaceable)

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24 | passivehouseplus.co.uk | issue 35

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CASE STUDY

grids to support the four panels that make up a typical house. At the time however, the team decided to go with an insulated concrete slab for Tim’s house because they were unsure if their pier foundation would meet passive house criteria, leading to a “slight disappointment for us and for Tim”, says Kinghorn. “Looking back, we were maybe a little over-cautious as it was our first passive house build.”

The final result is a lovely, understated home that really blends well into its environment, while on the inside, there is a real character to the rooms, from Tim’s study / music room, to the roof-lit mezzanine level that brings light down to the dining area through a slatted timber screen.

“It really feels like a home, says Kinghorn.

“I think we responded to Tim’s brief well — creating that strong link to the outdoors, and playing with height and light to make some areas cosier while other areas feel bigger and higher.”

“A really important part of the brief was a connection to the outdoors and the garden from inside, with sheltered outside space — commonly referred to as ‘sitooteries’,” added Kinghorn.

Although the house requires very little by way of space heating, Tim chose to install a wood burning boiler stove, which supplies hot water to two radiators as well as domestic hot water. The hot water is also supplemented by solar thermal panels and PV panels (the PVs are linked to an immersion heater, mostly used in the summer months).

A rainwater harvesting system supplies water to the WCs, washing machine and garden, while an electric car charging point is located by the main door.

Tim has been living in the house since September 2019, and is delighted. “Where do I start? The house fits beautifully into the landscape. Everyone bar none has said that they like the look of the house. Its energy efficiency is looking promising in these early days. It responds very well to the weather and is warm in the winter and pleasantly cool in the summer. It’s easy to live in and to keep clean.”

He reports that since his smart meter was installed in February this year, he has used 684 kW of electricty from the grid and exported 2,106 kW. “The house is roughly twice the floor area of my old one yet the running costs are around a third compared with previously. Once I start to receive the export tariff the costs may reduce again.”

Kinghorn describes Tim’s house as a labour of love. It may have taken more than a year from start to finish, but the result is a passive house system that can be easily replicated, and likely to take less time to build for future clients. Furthermore, the firm won two awards for it from the Alliance for Sustainable Building Products in the Best New Build and Best Product categories.

“Now we have a passive-compliant off-site system that we can replicate time and time again,” she says.

SCOTLAND

WANT TO KNOW MORE? The digital version of this magazine includes access to exclusive galleries of architectural drawings.

The digital magazine is available to subscribers on www.passive.ie

SELECTED PROJECT DETAILS Client: Tim Dawson Architect: Makar Civil & structural engineer: SF Structures Build system: Makar Contractor & project management: Makar Passive House certifier: Passivhusbyrån Ingo Theoboldt Electrical contractor: ICM Electrics Airtightness tester/ MVHR installer: Airtight Build Airtightness tapes: Siga Windows & doors: Internorm by Scotia Cellulose insulation: Warmcel, via PYC Group Wood fibre insulation: NBT / Soprema Floor insulation: Quinn Building Products / Kingspan Thermal blocks: Forterra Roof lights: Fakro, via Caley Timber Boiler stove, thermal store & solar thermal: Ashburn Stoves Solar PV: AES Solar Heat recovery ventilation: Paul, via Airtight Build Rainwater harvesting: Rainwater Harvesting Ltd Kitchen: Howdens Larch cladding: BSW Flooring: Russwood Roofing: Nu-Style Products Drainage design: Caintech Ltd

ph+ | scotland case study | 25

SCOTLAND

CASE STUDY

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26 | passivehouseplus.co.uk | issue 35

CASE STUDY

SCOTLAND

IN DETAIL Building type: 137 m2 (treated floor area) 1.5 storey 3-bedroom detached house built w/ prefabricated timber system.

used 684 kW of grid electricity. House electricity consumption includes electric car charging.

Site & location: Strathpeffer, Easter Ross, Highlands. Built in garden of a derelict bungalow on the outskirts of the village.

Thermal bridging: Thermal bridging was largely avoided through the use of an external 180 mm wrapped wood-fibre board insulation. All bridges were calculated using Therm software, and checked by the PH certifier. Ambient thermal bridges: 159m at 0.003 W/mK. Perimeter thermal bridges: 48m at 0.007 W/mK

Completion date: September 2019 Budget: £365,000 ‘turn-key’ construction cost Passive house certification: Passive House Classic certified Space heating demand (PHPP): 15 kWh/m2/yr Heat load (PHPP): 12 W/m2 Primary energy non-renewable (PHPP): 62 kWh/m2/yr Primary energy renewable (PHPP): 145 kWh/m2/yr Renewable energy generation (PHPP): 69 kWh/m2/yr (relative to building footprint) Heat loss form factor (PHPP): 2.62 Overheating (PHPP): 0% of hours above 25C Number of occupants: 1 Airtightness (at 50 Pascals): 0.34 ACH Energy performance certificate (EPC): A 115 Measured energy consumption: From October 2019 to July 2020 inclusive (10 months), the house consumed 2,973 kWh of grid electricity. Over the same time period the solar PV array generated 4,324 kWh. A smart meter was installed in February 2020, and from then until July 2020 inclusive the house exported 2,106 kWh of solar electricity, consumed 1,618 kWh of solar generated electricity, and

Energy bills (measured or estimated): Tim Dawson’s electricity bill averages to £35 a month for grid electricity, which includes some hot water generation but no space heating. He does not receive a feed-in-tariff for exported electricity. All wood used so far for the wood burning boiler stove has been from site offcuts.

Ground floor: Hardwood floor finish on 45 mm battened service zone, on 125 mm reinforced concrete slab, on slip membrane, on 300 mm Quinn Therm ground floor insulation, on 1200 g DPM, on 150 mm sand blinded hardcore. Perimeter load bearing Thermalite Aircrete Trenchblock insulated externally with NBT plinth board.

U-value: 0.071 W/m2k Walls: 150x25 mm vertical board-on-board heartwood larch cladding on 38x50 mm horizontal battens, on 25x50 mm vertical battens, on prefabricated wall panel comprising: 180 mm Pavatex Isolair insulation board on C16 kiln-dried regularised untreated 245 mm studs with cellulose insulation, with 18 mm OSB 3 internal lining board as airtight layer taped at all junctions. Internally there is a 45 mm battened service zone insulated with Pavaflex wood fibre insulation, finished with 12.5 mm plasterboard, taped and filled.

U-value: 0.091 W/m2k Roof: Anthracite grey big six profile metal roofing on 50x50 mm battens, on 120x50 mm Douglas fir secondary rafters screwed

to prefabricated roof panel comprising: Roofshield membrane on 180 mm Isolair wood fibre insulation, on 245 mm C16 kiln-dried regularised untreated rafters with cellulose insulation, lined internally with 18 mm OSB 3 airtight layer, all junctions taped.

45 mm internal service zone insulated with Pavaflex wood-fibre batts. 12.5 mm plasterboard internally, taped and filled.

U-value: 0.090 W/m2k Windows: Internorm HF310 aluminium/timber composite triple glazed windows.

Average installed U value average: U-value: 0.8 W/m2k Roof windows: Fakro FTT U8 Thermo triple glazed roof windows. Average installed U-value: 0.94 W/m2k Heating system: Verner 13/10.2 wood burning boiler stove linked to large thermal store feeding 2 x radiators and 2 x towel rails. The thermal store is also fed by the solar thermal panels and is topped up by immersion via the PV electric panels. The solar thermal array generated 2,000 kWh of energy between November 2019 and July 2020 inclusive.

Ventilation: Paul Novus 300, Passive House Institute certified to effective heat recovery efficiency 93%.

Water: A rainwater harvesting system is installed, which supplies both WCs, the washing machine and garden taps.

Electricity: 6.87 kW solar PV array. Once the thermal store is up to temperature the PV panels automatically divert to the electric car charging point. See ‘measured energy consumption’ above for PV kWh generated & exported.

Green materials: Dwelling uses natural materials in an off-site system that can be easily reproduced to meet the PH standard.

Local timber for wall panels and cladding, wood fibre and cellulose insulation.

ph+ | scotland case study | 27

HILL HOUSE

CASE STUDY

ENERGY BILLS

£21

PER MONTH FOR SPACE HEATING (estimate, see ‘In detail’ for more)

Building: 119 m2 detached passive house Build method: Structural insulated panels (SIPs) Site & location: Semi-rural site, Lewes, East Sussex Standard: Passive house classic certified

PECKING

ORDER

AWARD-WINNING PASSIVE HOUSE MAKES AN ELEGANT MARK ON THE SOUTH DOWNS Despite the challenges of getting planning permission within a national park, a new passive house on a hillside in the South Downs managed to woo the planners with a sympathetic, discerning design inspired by a surprising source — two dilapidated old chicken sheds.

Words by David W Smith

28 | passivehouseplus.co.uk | issue 35

CASE STUDY

T

His imagination was fired by a pair of disused chicken sheds.

he architect Charles Meloy – who has built the first passive house in the Sussex Downs National Park (SDNP) – dreamed for “decades” of building an affordable, sustainable house in this beautiful landscape. But not only was it prohibitively expensive, there were also restrictions on the types of developments allowed. Active searches for a suitable, economical plot proved futile. Then, one day back in 2013, Charles was relaxing on a walk across the Sussex Downs with a friend when his imagination was fired by a pair of disused chicken sheds a few minutes’ walk from Lewes.

“We used to do a walk on an ancient drove road used by fisher folk to carry fresh fish from Brighton to the county town of Lewes.

I wouldn’t be much of a developer as it was actually the third time I’d walked past the site before I noticed two dilapidated chicken sheds in a garden,” he says. “It suddenly struck me that we could build a house on the land and design it in a way that carried echoes of the original sheds.”

Charles quickly entered into a conversation with the owner who used the sheds for storage. He struck up a provisional verbal agreement to buy the land that was later formalised. The sale for a pre-determined price was conditional on Charles receiving planning permission on the site, which is outside of the Lewes town boundary but within the national park.

HILL HOUSE

Despite this challenge, Charles was confident of getting planning permission when he filled in his application in 2014. “We had a lot of things going for us. The use of the land was residential as we were effectively building on a section of their garden. Another plus was that the existing buildings were still there, and they were dilapidated, so we could prove that a new structure would lead to an ‘enhancement and promotion’ of the use of the national park, which is one of the key criteria for planning. We placed Sussex bullock hedging right along the roadside to blend into the surrounding landscape and we used untreated western red cedar that weathers over time and blends in beautifully with the surrounding woodlands,” he says.

Charles took care to get all his future neighbours on side. He met the owners of the three houses that are adjacent to the site and explained his plans. Everyone reacted enthusiastically. Charles then showed his design to the local conservation group Friends of Lewes, who were equally supportive. “I think when you prepare a planning application, it’s about being neighbourly and polite. If you don’t take the time to explain everything to all the stakeholders, the danger is that when they get the planning letter, it comes as a shock.

An unexpected planning letter can land as heavy as a lump of lead when it comes through their door.”

A lot of the support was inspired by his

ph+ | hill house case study | 29

HILL HOUSE

CASE STUDY

(above) The passive house certified Hill House, with the dilapidated chicken sheds that were originally on the site (inset).

elegant and sympathetic design. The essence of his concept was that the two new singlestorey buildings would carry a memory of the original chicken sheds. The two sheds had covered an area of 100 m2, whereas the completed house, which also utilises the gap between the sheds, is 125 m2. Charles was fortunate in that the original L-shaped layout, although not ideal from a heat loss perspective due to the large surface area, allowed for the living and sleeping areas to be split, with the open plan living area having a southerly aspect to benefit from solar gain in winter.

The first shed was replaced with an open-plan space with living room and kitchen. Meanwhile, the second ‘shed’ with the bedrooms was fitted with east-facing windows that provide morning light.

30 | passivehouseplus.co.uk | issue 35

In between, Charles designed a linking section for the service core, “We didn’t have to fight the existing form one bit. Open plan areas can be sprawling, but the detachment of the two sections gave us some definition,” he says.

Charles was committed to building a passive house, but not at the cost of the aesthetics. He was adamant that the architectural design had to come first. “That might not be music to some passive house designers, but it was an attempt to see if there really were any restrictions implied by the design when aiming for [the passive house standard]. If there were, they had to be integrated into a coherent piece of architecture,” he says.

Prioritising the architecture set additional challenges for the passive house consultant

Everything has been designed exactly as we want, and everything works as planned.

CASE STUDY

HILL HOUSE

Dan Gibbons, founder of Ape Architecture & Design in London. Charles and Dan have known each other since they shared a flat as students of architecture in Edinburgh and have a good rapport. “It was satisfying working with Charles from an architectural point of view. With a lot of passive houses I’ve worked in, the project has been driven by what makes sense for PHPP [the passive house design software], whereas Charles emphasised the design. It meant I had to up my game to come up with solutions to offset some of the more compromised areas,” Dan says. “And it stands up as a very architectural passive house, whereas a lot of them can look a bit lumpen and unfinessed. More often than not it becomes more about the best performance quality than whether it looks good.”

One complicating factor was that Charles wanted to express the ground floor slab on the outside of the building for aesthetic reasons, whereas a more common method for a passive house would be to insulate the ground slab externally.

“It made it harder to achieve [the passive standard], but for Charles it was a line in the sand,” Dan says. “We had a lot of discussions and spent a lot of time going back and forth working out the details. We had to work around having an exposed structural slab on the side of the building, then an insulated screed internally, while making sure we could still get the structural connection between the slab and the SIP (structural insulated panel) frame without there being a detrimental thermal bridge. But we managed it and it meant we got a very clear line aesthetically on the outside of building where you can see the concrete slab before

Photography: Charles Meloy

ph+ | hill house case study | 31

HILL HOUSE

CASE STUDY

Charles wanted to express the ground floor slab on the outside of the building.

the timber starts.”

Dan recalled having “lots of amusing discussions” about the window designs.

“Charles initially wanted to finish off the timber frames at the window reveals which relied on some large pieces of aluminium framing,” he says.” But this would have created a large thermal bridge that sucked heat out of the building.

“We had to do some careful modelling to make sure the aluminium was not directly connected to the windows. We also had lots of discussions about the window suppliers as when we were running the PHPP numbers and considering the windows Charles wanted, we always had to take into account his budget. After a few alterations, we eventually found a supplier with the performance we needed for the price he was willing to pay.”

Budgetary considerations were behind Charles’ decision to use SIP panels for the frame. SIPs are essentially a ‘sandwich’ of insulation, often polyurethane foam but in

32 | passivehouseplus.co.uk | issue 35

this case EPS, between two structural boards like OSB. Charles wanted the structure above ground to be lightweight to offset all the heavy elements touching the ground, including the concrete internal flooring and the exposed concrete at the base outside.

Timber frame was considered, but the SIP option was more economical and the suppliers were able to install them quickly.

For Dan, it was the first time he had worked on a passive house using SIP frames. “My preference would still be for timber frame with natural insulation, but the SIP panels made it easy to achieve the blanket U-values we needed from the walls by insulating correctly,” he says.

To manage costs, Charles took charge of almost the entire build. He continued to work four days a week for his Brightonbased practice Meloy Architects, but in the evenings, he drove down to the site and often didn’t stop work until midnight. The fifth day of each working week was devoted to his self-build, as was one day every

weekend. At times, he was helped out by a friend he had met years earlier on a bus trip in Australia, and who was training to be a teacher in Lewes.

Together, they installed all the insulation in the floor and added the cladding on the outside of the house. They also did the stud work, took care of the plaster boarding and fitted the internal doors. “It was tiring, but I had no option but to keep going until I’d finished. I worked out we used 10,000 screws for the cladding outside. But you actually get pretty efficient after you’ve done 1,000 or so!”

Charles employed sub-contractors for specialist jobs, such as the groundwork, fitting the SIP frame, the windows and the concrete flooring. Sub-contractors also helped out with the bathroom and the cabinetry. “The build went smoothly. It was the opposite of one of those Grand Design style TV programmes where everything keeps going wrong!”

With Charles doing most of the work a huge

CASE STUDY

HILL HOUSE

CONSTRUCTION IN PROGRESS

1

2

3

4

5

6

7

8

9

1 The ground floor concrete slab was left exposed on the outside of the building for aesthetic reasons; 2 erection of the SIPS frame underway; 3 210 mm Xtratherm Thin-R insulation covers the floor; 4 laid on top of this is a 110 mm screed; 5 Intello airtightness membranes and taping on walls and pitched roof; 6 this is followed inside by more Xtratherm Thin-R insulation on walls and roof, and then 25 mm timber studs forming services cavity on walls; 7 after that, there is further layer of OSB inside; 8 architect Charles Meloy with his wife Hannah and their children on the site; 9 Western red cedar external cladding on walls and roof.

ph+ | hill house case study | 33

HILL HOUSE

CASE STUDY

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34 | passivehouseplus.co.uk | issue 35

THE STREET

CASE STUDY

amount of money was saved, and Hill House cost a very reasonable £250,000 to construct (not including the cost of the land). Last year, it won four separate RIBA awards — in the south east, sustainability and small project categories, as well as a national award.

Despite the focus on design, the passive house standard was achieved comfortably, and the building offers exceptional thermal performance and airtightness.

Hot water is generated with an air source heat pump and extra space heating can be provided through a sealed wood burning stove. Charles lives with his wife and three small children at the property, which is near to the village of Kingston and a 10-minute walk into Lewes. Sat on the top of a breezy hill which was once home to Lewes’ windmills, it’s in the countryside, but near schools and amenities. “It’s a huge change from the very tall, tight townhouse we had before in Brighton, and we love it. Everything has been designed exactly as we want, and everything works as planned,” he says.

HILL HOUSE

WANT TO KNOW MORE? The digital version of this magazine includes access to exclusive galleries of architectural drawings.

The digital magazine is available to subscribers on www.passive.ie

SELECTED PROJECT DETAILS Architect: Meloy Architects Passive house consultant: Ape Architecture & Design Mechanical and electrical consultant: Alan Clarke Structural consultant: Reaction Engineers Passive house certification: MEAD Consulting Planning consultant: Pro Planning Arboriculturalist / ecologist: PJC Consultancy Daylighting assessment: DeltaGreen Foundations: SMD Formwork Steelwork: South Coast Steel Windows and doors: Doorstop Southwest Ltd Roof lights: Solar Vision Ltd MVHR: Systemair Heat pump: Ariston Airtightness testing: Tophouse Assessments Build system: SIPS Eco Additional wall & roof insulation: Xtratherm Thermal breaks: Armadillo Plates Airtightness products: Ecomerchant & Ty-Mawr Lime Ltd Underfloor heating: Heat Mat, via BTR Tech External blinds: Hella Roofing: DMB Flat Roofing Ltd Electrical: John Wadham Plastering: Rafferty (Plasterers) Ltd Landscaping: Worman Construction Ironmongery / doors: Aspex Concrete flooring: Steysons Granolithic Cedar cladding: Wenban Smith Sanitaryware: CP Hart Wood-burning stove: Westfire LED Lighting: Lightfoot LED Permeable paving: Tuff Turf Wastewater treatment system: Klargester Biodisc Cabinetry / kitchen: JM Furniture

ph+ | hill house case study | 35

HILL HOUSE

CASE STUDY

UNDERSTANDING PASSIVHAUS by architectural technologist, Emma Walshaw. A simple guide to the Passivhaus standard, explaining the principles behind Passivhaus thinking, exploring numerous construction methods for achieving the Passivhaus standard.

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Mechanical Ventilation with Heat Recovery Build by www.pycconstruction.co.uk

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E: info@pycgroup.co.uk T: 01938 500 797 36 | passivehouseplus.co.uk | issue 35

Recycled raw material. Low carbon footprint W: www.warmcel.co.uk

To comply with Building Regulations 2010 Part F & The Passivhaus Standard * Off-Plan Specification * Site Survey * CAD Design Service * Full Materials Package * Turnkey or Technical Support * Commissioning and Certification * Annual Service and Maintenance Se

Geothermal Options Available Office 3, Innovation House, Discovery Park, Sandwich, Kent, CT13 9FF

CASE STUDY

HILL HOUSE

IN DETAIL Building type: 120 m2 SIPs passive house Location: Lewes, East Sussex Completion date: Jan 2017 Budget: £250,000 Passive house certification: Passive house classic certified Space heating demand (PHPP): 13 kWh/m2/yr Heat load (PHPP): 12 W/m2 Primary energy demand (PHPP): 110 kWh/m2/yr Primary energy renewable (PHPP): 51 kWh/m2/yr Hot water demand (PHPP): 17.2 kWh/m2/yr Heat loss form factor (PHPP): 4.38 Overheating (PHPP): 0% of year above 25C Number of occupants: 4 Airtightness (at 50 Pascals): 0.6 air changes per hour Energy performance certificate (EPC): B 89 Thermal bridging: Critical thermal bridges, slab edges, steel beams, window frames

etc were modelled in Therm – establishing an average Psi value of 0.012. All remaining thermal bridges were left as the PHPP default of 0.01 even though sample modelling of the standard SIPs details suggested that lower Psi values were being achieved.

Energy bills (measured or estimated): Based on final energy demand figures in PHPP, USwitch.com suggests a lowest available annual space heating bill of £248, or £20.66 per month, and hot water bill of £259, or £21.58 per month. Figures include VAT but not standing charges. Space heating figures do not include the wood burning stove, for which all wood so far has come from the site.

Ground floor: 110 mm screed over 210 mm Xtratherm Thin-R insulation over 200 mm concrete slab. U-value: 0.101 W/m2K Walls: Western red cedar external cladding on battens and counter battens, followed inside by Tyvek UV Facade breather membrane, structural insulated panel comprising 172 mm SIPS Eco EPS insulation sandwiched between 11 mm OSB boards, Intello air tightness membrane, 60 mm Xtratherm Thin-R insulation, 25 mm timber studs forming services cavity, 11 mm OSB, plasterboard. U-value: 0.108 W/m2K. Pitched roof: Western red cedar external cladding on battens and counter battens, followed inside by roof deck, Tyvek UV Facade breather membrane, SIPS Eco Structural insulated panel comprising 172 mm

EPS insulation sandwiched between 11 mm OSB boards, Intello air tightness membrane, 80 mm Xtratherm Thin-R, plasterboard.

U-value: 0.108 W/m2K. Flat roof: Single ply membrane, followed beneath by 18 mm plywood to falls, 120 mm Xtratherm Thin-R, 18 mm plywood, 50 mm Xtratherm Thin-R between joists, ventilated cavity followed underneath Intello air tightness membrane, plasterboard.

U-value: 0.123 W/m2K. Windows & external doors: HON Quadrant Studio FB IV-9 timber-aluminium windows and doors. Typical spec: 44 mm triple glazing with Saint-Gobain ClimaPlus Ultra N glass & a Swiss spacer bar. Ug value: 0.50 W/m2K, dB value: 34, average overall U-Value: 0.80 W/m2K. Roof windows: Vitral 4-degree Skyvision Comfort triple glazed Ecoline openable rooflights & Vitral 4 Skyvision Ecoline frame-only fixed rooflights. Ecoline glass, 32 mm low-e, krypton fill. Ug = 0.7 W/m²K. Heating system: Ariston Nuos 250i heat pump for domestic hot water and also supplying duct heater in MVHR system, plus underfloor heating if needed in extreme weather. Westfire 35 standalone wood burning stove.

Ventilation: Systemair VTC 200 MVHR system. Passive House Institute certified heat recovery rate of 90%.

ph+ | hill house case study | 37

ENERPHIT

CASE STUDY

ENERGY BILLS

€20

PER MONTH FOR SPACE HEATING (estimate, see ‘In detail’ for more)

Building: 265 m2 deep retrofit of 1950s detached house Site & location: Linaro Avenue, Magazine Road, Cork City Standard: Enerphit certification pending

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CASE STUDY

ENERPHIT

SPECULATIVE E FFORT

EXTRAORDINARY A1 CORK UPGRADE IS IRELAND’S FIRST DEVELOPER LED ENERPHIT

In 2016, builder David Lane decided to buy a large 1950s house in Cork city and undertake a tricky deep retrofit, turning the run-down property into an upmarket passive house. It’s about as far from the traditional model of property development as you can imagine — but it holds some crucial lessons for what we do with our urban buildings in the era of climate breakdown.

Words by John Cradden

ph+ | enerphit case study | 39

ENERPHIT

CASE STUDY

I

f you’re a developer with a high-end fixer-upper property to work on, not so long ago you might have spent your money just commissioning the necessary structural repair work, fitting new windows and maybe a new heating system, and doing a decent cosmetic job inside and out before selling it on for a reasonable profit.

However, buyers looking for a walk-in property at the upper end of the market today do expect a bit more in terms of eco-cred, including a BER rating in one of the three A bands. After all, you might well boast about your newly renovated home’s luxury and beauty, but if you can’t brag about the fact that you rarely need to turn on the heating or that you generate surplus electricity from your PV panels, then you might feel like you’re missing out a little bit.

Some developers are responding to changing demands and expectations when it comes to comfort and energy performance, but this house on Linaro Avenue in Cork city represents one of the most comprehensive energy retrofits in Ireland to date.

Recently put on the market for €1.25 million, this circa 1950s five-bedroom home has been rebuilt to the Enerphit standard – the passive house benchmark for retrofit projects — along with a two-storey side extension and a single-storey rear extension. It’s one of only a handful of Enerphit certified homes in Ireland, but it’s the first to be done with a view to selling.

“There might be a good reason for that, because they tend to be labours of love,” says developer David Lane of Lough Contractors.

Lane had learnt all about energy efficient technology and construction methods through a course he did in the Cork Institute of Technology (CIT) back in 2011, which was followed shortly after by a CIT-hosted two-week trip to Germany to have a look at what was happening there in terms of energy efficient building. He then studied to become a certified passive house consultant in 2012.

So, the idea of building to the Enerphit standard emerged back in 2016 when his firm bought the house. The property was in fairly poor condition cosmetically, but structurally it was okay. “In many ways we feel that perhaps we should have knocked it, but it was a relatively substantial house with a really good aspect and an interesting enough layout within that we felt we could develop,” says Lane.

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CASE STUDY

With solid block walls, no insulation, no cavity, and three large chimney shots, “it almost cried out to have this retrofit action put upon it, because it was so obviously not built with any thermodynamics in mind,” he says.

With a plan to undertake the project in the downtime between other jobs and thereby give himself at least a couple of years to finish it, Lane drafted in passive house designer Paul McNally of the Passivhaus Architecture Company as part of a team that included architect Paul Hudson, engineer Declan Daly of Concept Design, and interior and garden designer Keith Spillane.

McNally is one of Ireland’s longest-serving passive house designers, with a track record stretching back to the early noughties, including on one other Enerphit project. He is full of praise for the decision to retain the original building rather than knock it and displace the embodied energy, although

Applying external insulation to a 1950s home with a painted wet dash finish was hard work.

Photography: Jed Niezgoda

he acknowledges that the additional cost of doing so versus what would have been spent on a new build means the financial advantages are not so cut and dried.

When the design of the extensions was finalised and then given the PHPP modelling once-over, McNally reports that he didn’t have to recommend any onerous changes for the design to meet the Enerphit standard.

“There wasn’t anything that had to be fundamentally changed,” he says. The main issue was looking at thermal bridging, particularly with the cantilever structure like bay windows. “That would have been just something that didn’t have to be redesigned, more that David just had to think very clearly about how he was going to address that as a detail from a construction point of view.”

Two of the now superfluous chimney shots were demolished as part of the extension works, which were kept largely within the footprint of a (now demolished) separate student bedsit block, to create the renovated 265 square metre dwelling. “You would see the shame in just knocking and rebuilding it,” says Lane. “You can never rebuild; you can never get the character back… and this house does retain its character.

In addition, all the old concrete floors, footpaths, kerbs, walls, chimney shafts and roof tiles that were stripped and demolished on site were crushed and used in the infill grading of the garden and driveway.

Talking to Lane, it does sound like there were several challenges in terms of preparing the building fabric for the airtight-

ENERPHIT

ness and insulation upgrades that, while not unexpected, proved quite frustrating to deal with.

As you’d expect, applying external insulation to the outside of a 1950s home with a painted wet dash finish of varying thicknesses was hard work, requiring a lot of “scrubbing, hacking and power washing” to get a clean even surface on which to apply the insulation. Not to mention the difficulty of ensuring that there were no air pockets between the wet dash and the original blockwork before the insulation was installed. “It was a more involved process than you would ever imagine,” he says.

That sheer hard graft extended to the job of fitting airtightness membranes in behind the retained floor joists of the original house, which involved a bit of trial and error.

Another challenge was that one new wall could not be fitted with external insulation due to its proximity to an existing boundary wall. The solution here was to shutter the space between the two walls with KORE EPS insulation, and then to pump-fill the shuttered void with polystyrene bead. The extension wall on this elevation was also built entirely from Roadstone Thermal Liteblock to improve its thermal performance too.

There are a few high-tech features, such as electric access gates, CCTV, category six cabling, wi-fi boosters and remote control Velux rooflights with solar-powered electric motors and sensors that close the windows when rain is detected, but it’s not over-done,

ph+ | enerphit case study | 41

ENERPHIT

CASE STUDY

FLOORS IN PROGRESS

1

2

3

4

5

6

1 The ground floor features 75 mm Kingspan TF70 incorporating lagged water distribution; 2 overlaid with 125 mm Kingspan TF70, plus 25 mm thick Kingspan TF70 border insulation; 3 foam insulation around service penetrations; 4 installation of the underfloor heating network; 5 pouring the 100 mm fibre reinforced concrete; 6 using a concrete float to smooth the finished surface.

EXTERNAL ENVELOPE IN PROGRESS

1

2

3

4

5

6

1 Compacfoam and infill insulation to windows; 2 external insulation block being installed under a window cill; 3 window cill detail; 4 200 mm Kore EPS installed over drip tray; 5 external insulation detail to boundary wall at rear of building; 6 insulation being installed around Velux roof window.

42 | passivehouseplus.co.uk | issue 35

CASE STUDY

and money has clearly been spent in all the right places. That includes some €200,000 on the groundworks, including a short run of limestone steps and a beautifully executed courtyard garden.

Along with solar photovoltaic panels, and an MVHR system from ProAir, the house also features a heat-pump powered, nine-zone heating system with underfloor heating throughout the ground floor, heated towel rails in all the bathrooms, and radiators in the first-floor bedrooms.

It is tacitly acknowledged that this is probably a bit of an overkill for an Enerphit property, but Paul McNally points out that when designing a passive house for a high-end commercial market, it’s not surprising that Lane would specify something like this.

He says that while a lot of clients understand that you can dial down the heating system to a small quantity of radiators or underfloor heating and still meet ambient comfort requirements in a passive house, others might want active heating all over, for what they perceive as greater uniformity or to have that nice, warm slab underfoot feeling.

“It’s more about an aesthetic to physical comfort rather than a cold engineering calculation,” McNally says. “If you had a potential client that really liked the house and liked the location but who wasn’t au fait with passive house theory and practice, you don’t want to exclude those kinds of people because they might be thinking, ‘Well, will this house be warm if it’s a passive building, do I trust the science?’ So those kinds of people can still be a potential purchaser for this house because it’s not a bare-bones passive house in terms of comfort.”

According to the property price register, Linaro House was bought in 2015 for €320,000. But despite the current £1.25m price tag, Lane says his profit margin won’t be massive due to the no-expense-spared approach, the aim of reaching Enerphit, the attention to detail and long project gestation.

The house already attracted a firm offer shortly after it went on the market in July.

Not surprisingly, Lane will be very sorry to see it go. “Although it might not have been a full-time project, it was certainly a kind of a full-time, ever-present, in-the-mind project,” he said. “It has occupied my head certainly for the last three and a half to four years and been hugely rewarding for such an emotional involvement.”

ENERPHIT

SELECTED PROJECT DETAILS Developer: Lough Contractors Architect: Hudson & Associates Civil & structural engineering: Concept Design Passive house consultant: The Passive House Architecture Company Main contractor: Lough Contractors Quantity surveyor: Synnott Scallan BER assessor: Start Energy Services Passive house certification: Earth Cycle Technologies Interior & garden design: Keith Spillane Mechanical contractor: Robert McGarry Plumbing & Heating Electrical contractor: Ger Callanan Electrical Airtightness tester/consultant: Air Matters External wall insulation: Kore, via HPS Group Thermal breaks: Compacfoam, via Partel Thermal blocks: Liteblock, via Roadstone Roof insulation: Rockprime, via HPS Group Additional roof insulation: Knauf, via

Brooks Floor insulation: Kingspan, via MD O’Shea & Sons Airtightness products: Siga, via Southwest Radon Airtightness products: Pro Clima, via Cork Builders Providers Liquid airtight membrane: Blowerproof Ireland Airtight mastic: Clean Energy Ireland Windows & doors: Viking, via West Building Products Roof windows: Velux Fit out: House of Coolmore Roofing membrane: Alkorplan, via CA Roofing Systems Roof tiles: Forticete, via Roadstone Limestone paving: Classic Driveways Planting: The Pavilion Garden Centre Heat pump & DHW tank: Daikin Towel rails: Irish International Trading Underfloor heating: Pipelife MVHR: ProAir Solar PV: PV Generation

WANT TO KNOW MORE? The digital version of this magazine includes access to exclusive galleries of architectural drawings.

The digital magazine is available to subscribers on www.passive.ie

ph+ | enerphit case study | 43

ENERPHIT

CASE STUDY

AIRTIGHTNESS IN PROGRESS

1

2

3

4

5

6

7

8

1 Solitex airtightness membrane behind strengthened joists; 2 airtightness plaster application on first floor; 3 wall service battening - concrete screw installation; 4 airtight tape and membrane at Velux window; 5 wall service battening and ceiling airtight membrane at main entrance; 6 airtight tape to window perimeters; 7 airtight plaster detail supplemented at reveals and cill with Blowerproof liquid airtight membrane; 8 heat recovery distribution to be connected to MVHR over utility room.

ROOF IN PROGRESS

1

2

3

1 Inter rafter insulation on back roof; 2 & 3 soffit insulation detail.

44 | passivehouseplus.co.uk | issue 35

It has been hugely rewarding for such an emotional involvement.

CASE STUDY

ENERPHIT

IN DETAIL Building type: 265 m (238 m TFA) deep retrofit & extension of 1950s detached house.

Two-storey side extension and single-storey rear extension.

Thermal Liteblock used in the deadwork of new wall build-ups. 220 mm collar of Xtratherm around two new Velux windows and around parapet of new flat roof.

Site & location: Linaro Avenue, Magazine Road, Cork City

EXISTING GROUND FLOOR Before: Uninsulated concrete floor. U Value: 0.5 W/m2K After: 804 hardcore fill, incorporating sewer runs, with limestone sand blinding under radon membrane. Followed above by 75 mm Kingspan TF70 incorporating lagged water distribution overlaid with 125 mm Kingspan TF70, plus 225 mm high, 25 mm thick Kingspan TF70 border insulation. 100 mm fibre reinforced concrete above, over 1000-gauge visqueen and underfloor heating network. U-value: 0.107 W/m2K

2

2

Budget: €750,000 (approx.)

Completion date: December 2019 Enerphit certification: Pre-submission BER Before: F (401.26 kWh/m2/yr) After: A1 (21.52 kWh/m2/yr) Space heating demand (PHPP): 18 kWh/m2/yr Heat load (PHPP): 9.72 Primary energy renewable (PHPP): 38 kWh/m2/yr Primary energy non-renewable (PHPP): 67 kWh/m2/yr Heat loss form factor (PHPP): 3.58 Overheating (PHPP): 7% (if year above 25C) Number of occupants: Not yet occupied Energy performance coefficient (EPC): 0.155 Carbon performance coefficient (CPC): 0.144 Measured energy consumption: Not available Energy bills: Based on final energy demand figures in PHPP, and assuming 50% of the energy generated by the PV array is used in the building, the total annual energy bill would be €785 (including VAT, but excluding standing charges and levies, using the lowest available tariff available via Bonkers. ie.) The PV is estimated to reduce the bill by 20%. Applying this reduction evenly to each energy load, this results an estimated annual space heating cost of €242 (€20 per month) and domestic hot water cost of €194.

AIRTIGHTNESS (at 50 Pascals) Before: Not tested After: 0.66 air changes per hour Thermal bridging: 75 mm deep Compacfoam blocks fitted under and alongside all window and doors to support and hold them inside the insulation envelope, subsequently dressed over with KORE EPS. Rafter fillet laid over rafters tapering from 220 mm at eaves to nothing approximately 2.5 m up each rafter, resulting in a 33-degree pitch bell-cast effect (40-degree pre-existing pitch) to reduce eaves thermal bridging. 135 mm Kingspan Kooltherm fitted between rafter fillets to run from plumb line of EWI to beyond full height of attic insulation. Roadstone

EXISTING WALLS Before: Painted external wet dash over block work of varying thicknesses and coated with sand, cement, skim coat and paint internally.

After: Weber external primer and finish coats over 200 mm of KORE silver EPS insulation bonded with adhesive to avoid any thermal bypass, over existing wet dash render.

Followed inside by blockwork of varying thicknesses. Sand and cement airtight render applied to interior with Blowerproof airtight sealant sprayed or brush painted to window reveals and some difficult pre-existing intersections. 35 mm battens fixed with concrete screws to form service cavities internally. 12.5 mm plasterboard slab and skim coat internally. U-value: 0.143 W/m2K NEW PITCHED ROOF Before: Concrete roof tiles on battens over bituminous felt, on cut roof pitched at 40 degrees. Glass fibre of 100 mm laid between ceiling joists over plasterboard and skim coat painted ceilings.

After: Forticrete SL8 roof tiles by Roadstone over 35 mm counter battens, over 35 mm rafter aligned batten, over Kingspan Nilvent breather felt dressed vertically to maintain draft exclusion. 135 mm Kingspan Kooltherm fitted between rafter fillets to run from plumb line of EWI to beyond full height of attic insulation. Rockwool Rock Prime insulation blown into attic to fill in between 112 mm ceiling joists and over 100 mm x 75 mm wall plates to meet EPS eaves insulation blocks, and to underside of rafters and inter rafter insulation to a height of 600 mm.

U-value: 0.077 W/m2K Extension floor: Concrete raft foundation with 804 hardcore fill, incorporating sewer runs, and limestone sand blinding under radon membrane. Followed above by 75 mm Kingspan TF70 insulation incorporating lagged water distribution overlaid with 125 mm Kingspan TF70 and 225 mm high, 25 mm Kingspan TF70 border insulation.

100 mm fibre reinforced concrete over 1000-gauge Visqueen and underfloor heating network. 0.107 W/m2K Extension walls: Weber external primer and

finish coats over 200 mm KORE silver EPS insulation bonded with adhesive to avoid any thermal bypass, on 225 mm block on flat and reinforced concrete heads with some steel lintels over Roadstone Thermal Liteblock 335 mm height deadwork, over min 110 mm height standard block deadwork. 35 mm battens fixed with concrete screws to form service cavities, 12.5 mm plasterboard slab and skim coat internally. U-value: 0.143 W/m2K Extension flat roof: Renolit Alkorplan PVC-P single ply roofing membrane, on 120 mm Xtratherm FR-ALU insulation over a further 100 mm Xtratherm FR-ALU, on Laydex torch on felt, on 18 mm Smartply OSB3.

Followed inside by 225 mm x 44 mm joists supporting the OSB layer, cavity filled with Knauf Earthwool insulation, on SIGA Majpell membrane, on 35 mm battens oriented with the joists and at least 35 mm counter battens, on plasterboard and skim.

U-value: 0.067 W/m2K WINDOWS & DOORS Before: Double glazed PVC windows and doors with overall approx U-value of 2.8-3.0 W/m2K New triple glazed windows: Viking SW14 aluminium clad triple glazed timber windows and doors with Swisspacer Ultimate and two low-e coating. Overall average U-Value of 0.77 W/m2K. Viking DK88 timber front door.

Roof window: Velux passive house certified GGU 008230 with triple glazed outer glazing and double glazed inner glazing, thermally broken frame and solar powered operations including a rain sensor for automated closing.

Passive House Institute certified installed overall U-value: 0.8 W/m2K HEATING SYSTEM Before: 15-year-old natural gas boiler with radiators throughout entire building.

After: Daikin Altherma 7kW air-to-water monobloc heat pump with nine zone qual-pex underfloor heating system to ground floor with Fondital Lis-Cool towel rails throughout bathrooms and Milano Aruba radiators to first floor bedrooms.

VENTILATION Before: No ventilation system. Reliant on infiltration, 3 x chimneys and opening of windows for air changes.

After: ProAir PA 600LI Passive House Institute certified mechanical ventilation with heat recovery unit.

Electricity: 19 m2 of PV panels giving 3.56 kW average annual output. Power directed to general household electrical use. The PV system & house electrical use are all monitored by an installed Smappee system which will learn how the electricity in the house is being used. If excess solar PV is generated the Smappee system for example can direct the homeowner to switch on the heat pump to top up the hot water tank.

Allows for offsite control & monitoring.

ph+ | enerphit case study | 45

SOUTH DUBLIN

CASE STUDY

ENERGY BILLS

€393

PER YEAR FOR ALL ENERGY USE PLUS ELECTRIC VEHICLE (estimate, see ‘In detail’ for more) Building: 120 m2 detached passive mews house Build method: Single leaf aerated blockwork w/ external insulation Site & location: Suburban garden, Sandycove, Dublin Standard: Passive house ‘plus’ certification pending

46 | passivehouseplus.co.uk | issue 35

CASE STUDY

SOUTH DUBLIN

ZE R O IN INSPIRED DESIGN OFFERS ROUTE TO NET ZERO ENERGY LIVING

It sounds like an impossibility: a high density, architectural, zero energy home on the tightest of back garden sites, adaptable to the needs of everyone from empty nesters to a family of six without opening a toolbox. But sometimes a project comes along that redefines what is possible.

1490

Words by John Hearne, with additional reporting by Jeff Colley

First Floor Level 10.990

Terrace drainage and paving above deck services void

107

services void

476

734

596

2403

2510

3330

3090

2220 290

2910

REAR REARELEVATION ELEVATION

LONG SECTION LONG SECTION

sla te p itc ed "m ro o f

D3 C14

D5

D4

C14

C14

COVE MEWS

D4 C14

CRO SS SECTION CROSS SECTION

I

t’s hard to know where to start with Mel Reynolds’ new house in Dún Laoghaire. The first passive house ‘plus’ build in the country, it was financed with a crowd-sourced funding model. Its reconfigurable ground floor layout anticipates a range of human needs, and yet it still manages to achieve a far more efficient use of space than your traditional semi-d.

And because it delivers so much in a tight footprint, it offers developers a scalable model of highly efficient land use at no additional cost.

Perhaps the most striking thing however is the symbiosis Reynolds discovered between his take on the passive house plus

FRONT ELEVATION FRONT (NORTH) ELEVATION (NORTH)

standard and the operation of an electric vehicle. The savings – in both cash and CO2 – are jaw-dropping. More about that later.

Let’s start with some detail. This is a 120 m2 four-bed passive mews house built in the garden of Reynolds’ existing Sandycove home, which is itself a protected structure located in an architectural conservation area. The new mews house is of single leaf masonry construction with external wall insulation. It comfortably meets the passive standard, and with the addition of a sizeable PV solar array, is set to be certified as passive house ‘plus’. This recently-introduced version of the standard requires a minimum of 60 kWh/m2/yr of renewable

energy generation on site.

Finance for the build was raised through Property Bridges, an Irish organisation set up in the aftermath of the 2008 crash to step into the space the banks had largely vacated. It provides peer-to-peer loan finance for construction projects. Individuals can invest relatively small sums which are then repackaged into loan finance for specific projects. Reynolds’s house was the very first to be funded by the platform.

This is a mews house, and mews houses, as Reynolds points out, are typically quite austere and self-contained because they don’t tend to have a much of a streetscape to engage with. You’re also talking about a very

ph+ | south dublin case study | 47

SOUTH DUBLIN

CASE STUDY

compact infill site, overlooking not alone the existing family home but also adjoining houses in quite a densely populated suburb. This led to what he describes as an ‘introverted’ design, with no overlooking windows. “I was looking not alone from our point of view, but from the point of view of surrounding neighbours.”

Smart use of space It’s also an ‘upside down’ house. Bedrooms on the ground floor, kitchen and living area on the first floor.

“People assume that this is an aesthetic decision,” says Reynolds, “and it is, it’s an interesting way to live, but it actually is far more efficient internally in terms of your net usable space.”

He points out that the statistic that we all zero in on – floor area – can be misleading.

Net usable space, on the other hand, removes hallways, bathrooms, ensuites and undercrofts, giving you a more meaningful metric. The regulations insist on a bathroom on the same floor as the main entrance. Since this is now downstairs with the bedrooms, the main bathroom fulfils this role and there’s no need for any WC upstairs. The only circulation space, therefore, is the stairs ascending to the first floor.

“The net to gross ratio of circulation and service spaces to usable spaces in a typical four-bed semi-d or five-bed three-storey is between 30% and 33%. In this arrangement, it’s 20%. So you effectively get an extra bedroom by just inverting the layout...So even though this house has 120 m2 square metres gross space, internally, it’s the equivalent of about 135 m2.”

Throughout the build, Reynolds also

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CASE STUDY

Getting the right builder was critical to achieving the required airtightness.

Photography: Paul Tierney / Abdone.com

looked at the project with a developer’s eye; in terms of materials, in terms of design, in terms of logistics. The ‘introverted’ design and the highly efficient use of space make the proposition much more attractive to a developer willing to use a different cookie cutter. Reynolds estimates that you can get 30% greater density with this design, and it’s hard to see what you’d be giving up for that.

He originally conceived the project as a sort of trade down home for an older couple, but as he began to work through the design, he realized that the possibilities were much wider. “I tried to imagine a client in order not to get bogged down with what I wanted.

But there was always that tension between would it be for a couple or for a family?”

Rather than resolve that tension, he decided instead to try to “future proof for different occupancies”. Was there a way to configure the house so that it could meet the needs of a family or couple or... whatever?

The answer was yes.

Downstairs, the rooms can be reconfigured into no fewer than 16 different layouts, from five bedrooms to a single master suite.

This is done using a combination of folding partitions and ‘soft spots’, built-in openings in walls which can be disassembled and reassembled very easily.

“One of the issues with residential schemes is that they’re very rigid,” says Reynolds. “If it’s a one-bed apartment, it’s always going to be a one-bed apartment.

The same if it’s a co-living unit, a hotel room or a bedsit. None of these spaces can become anything else without significant

SOUTH DUBLIN

modifications. I was interested in this idea of resilience in the built environment. I wanted it to be a comfortable house for either a couple, a small family or a large family... So the design challenge was how do you fit a four-bed semi-d on a 135 m2 site with two car parking spaces, 60 m2 of garden space and a flexible interior?”

All of this is great in theory of course, but could a large family live comfortably in this space? Is it simply too small to work? It was to answer this question that Reynolds and his family of six (partner plus four children) decided to move in. He sold the idea to the kids by offering them their own rooms – something they didn’t have in their existing house, despite the fact that it’s got twice the floor area. Similarly, despite the compactness of the design, there is more storage space in the mews house than in the old house.

All of the design work evolved under the constraint of a passive standard thermal envelope. As far as the build went, Reynolds brought to bear all of the work he had been doing in the previous two decades, refining details and arriving at a fabric spec that would achieve the necessary targets as simply as possible.

Super insulated masonry He opted for single leaf masonry with external insulation, a specification he has been using since 2008, combining Quinn Lite thermal blocks with Kingspan phenolic external insulation and acrylic render to deliver passive house U-values.

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SOUTH DUBLIN

CASE STUDY

Quinn’s low thermal conductivity aerated concrete blocks have been used for years as the first course on many masonry builds as a mean of eliminating thermal bridging between the walls and the floor slab. But since 2018 the company has been promoting the use of Quinn Lite blocks with external insulation for single-leaf, whole-wall construction, dubbing it their “super insulated masonry solution”, or SIMS. “By using Quinn Lite as the masonry substrate, you’re automatically improving the thermal performance or U-value of the walls, while at the same time significantly reducing thermal bridging throughout the building,” says Jason Martin of Quinn Building Products.

Single-leaf blockwork also helps to speed up the build, with the lightness of aerated blocks making things easier again.

“In relation to the speed of build, if you compare it to typical cavity wall construction, you’re using half the number of blocks. For a square metre of wall, you only need ten blocks, so first off, it’s much, much quicker than building a traditional cavity wall,” says Jason Martin.

Reynolds also says that aerated blocks contribute to faster drying time, and even though they cost more per block, the need for less blocks and less labour makes it cost neutral overall. As is frequently the case, airtightness was a challenge, and was met in this case with a Blowerproof liquid airtight membrane, which Reynolds discovered in the pages of Passive House Plus. This is a BBA certified product with Class C fire rating and is well established in Europe.

While the normal fire compartmentation requirement with a build-up like this would be to batten out the walls internally and then mechanically fix plasterboard to the battens, Reynolds established that it was acceptable in this case to use dabs of adhesive to glue the plasterboard directly to the Blowerproof-painted walls, because Quinn Lite has a four-hour fire rating on its own. This helped save valuable floor space as well as speed up the build.

He admits that getting airtightness down below the magic 0.6 ACH at 50 Pa can be time consuming and tricky, but that it’s uniquely worthwhile.

He says getting the right builder was critical to achieving the required airtightness. “The builder Sean Regan had comple-

Downstairs, the rooms can be reconfigured into no fewer than 16 different layouts.

50 | passivehouseplus.co.uk | issue 35

ted the Passive House Academy’s tradesperson course and had two skilled foreman, John Gorry and Sean Whelan, who both had training in airtightness. Without this essential upskilling on the contractor’s side it would have been very difficult to get to this level of quality, particularly the airtightness.”

Ultimately the team’s prior experience paid off. “The airtightness was the most challenging aspect,” says contractor Sean Regan. “It was just about being meticulous and checking and rechecking. It was our first time using Blowerproof, but it was very convenient around window openings and tricky corners.” The same team — Reynolds and contractor Sean Regan — is now working on a passive retrofit project in Rathgar, again using Blowerproof for airtightness.

Passive house ‘plus’ Reynolds refers to both Madeira Oaks, a 2016 passive development in Enniscorthy

by Michael Bennett, and Silken Park, a

Durkan Residential passive house development in City West, as inspirations behind this project.

“These showed us that if you can hit passive levels of fabric performance, you don’t need a primary heating system, you can do it using an airborne system. So straight away, if you can spend a little bit more on your walls, particularly on glazing, and make it airtight, you can eliminate your boiler and save about fifteen thousand euros.”

Reynolds’s next question was what to do with the savings. One possibility? Put it on the roof. He specified a very large solar PV array of 24 panels covering an area of 41 m2, with a power rating of 6.8 kW. Chatting to a neighbour about his plans, she mentioned that her dad worked with PV. This dad turned out to be Tim Cooper – one of the foremost experts in the country. Cooper agreed to come and look at Reynolds’ plans.

This was his first question: ‘What are you going to do with the power? If your house is efficient, you’ll be exporting most of it.’

CASE STUDY

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The foundations spec includes 1 a concrete trench; 2 perimeter of Quinn Lite and Foamglas blockwork; 3 270 mm Kingspan K3 insulation followed by reinforced concrete slab mesh; 4 corner detail showing XPS insulation enclosing the first layer of Quinn Lite block. 5 Singleleaf Quinn Lite blocks form the whole walls, significantly reducing thermal bridging throughout the building. 6 Kingspan phenolic external insulation helps to deliver passive house U-values; 7 & 8 200 mm Kingspan external wall board insulation is fitted to the soffit at the overhang and undercroft; 9 Compacfoam supports to window reveals minimise thermal bridging.

By Cooper’s calculations, between 60% and 70% of the power would be going back to the grid. Moreover, the way electricity demands varied from morning to evening, there would be days when Reynolds would both import and export power – and there remains no feed-in tariff in Ireland for microgenerators.

Rather than scrap his plans, Reynolds asked Cooper if he would create a demand control model which would determine the most efficient way to use the power he intended to generate. Straight away, Cooper spotted a couple of easy wins.

“Mel intended to use cold-fill washing machines,” he says, “which would be

heating up the water with electricity, and in an uncontrolled way. We decided to get hot-fill washing machines [which use hot water already generated in the home] so you could heat the water in an efficient way.

That was step one.”

Next, they made sure that all the electrical appliances had AAA energy ratings to cut instantaneous power use, thereby reducing potential demand on the grid. That done, they looked at the storage options, specifically batteries and thermal storage.

“We did a lot of arithmetic,” says Cooper, “and concluded that the most efficient way to do it in all respects was to put in an increased thermal hot water storage system

and design it in such a way that it was fully optimised.”

The house has a Pichler PKOM4 combi heat pump system supplying all space heating, hot water and ventilation duties.

The Pichler unit has an integrated 212 litre hot water tank, but Reynolds and Cooper decided to install another 120 litre tank to increase the storage capacity for hot water generated by the solar PV array. The heat pump was also configured so that it always heats water in the coolest tank first, to maximise efficiency.

There is also a seven litre Quooker boiling water tank and associated tap, again powered by the PV. In addition, Reynolds

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CONSTRUCTION IN PROGRESS

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1 & 2 With the ground floor structure complete, work begins on the upper floor of the house which includes an outdoor terrace. 3, 4 & 5 the front door and hall, showing Blowerproof liquid airtight membrane being applied directly to the Quinn Lite blocks, and plasterboard fitted directly to the Blowerproof-painted walls. 6 Siga Majrex airtightness membrane and tapes around roof windows; 7 the Fakro walk-on roof windows are situated flush with the tiles of the first-floor terrace. 8 A Pichler combi heat pump system supplies all space heating, hot water and ventilation duties; 9 the large 24 panel solar PV array not only generates plenty of power to use around the home, it can also produce enough energy to run an electric vehicle for 10,000 km per year.

installed a 4.8 kW solar battery pack.

According to Tim Cooper’s model, total energy costs would come to €1,017 per year with six occupants if there was no solar PV. That’s 6,908 kWh of energy and 2,010 kg of CO2 for all space heating, hot water and plug loads. But when you bring in the combination of PV, thermal storage and battery pack, consumption of grid electricity drops by 70% to just €300 per year (2,244 kWh), with a surplus of 976 kWh being exported.

It was at this point that Reynolds began looking at the possibility of diverting that excess into an electric vehicle (EV). The figures

52 | passivehouseplus.co.uk | issue 35

which fell out of the model were fascinating.

The house’s PV array could power the car for two-thirds of his annual mileage of 15,000 km, with one-third (5,000 km) coming from the grid at a cost of just €93. And this left the house exporting just 613 kWh of leftover solar energy back to the grid.

“In effect,” says Reynolds, “at passive house mews a typical EV will have annual fuel bills of €93 for 15,000 km average annual driving, as opposed to an efficient diesel which costs €926 per year to run, and generates 1,871 kg of CO2 for the equivalent mileage. Moreover, the passive house plus mews, plus EV actually emit three tonnes less CO2 than the average

NZEB A3 home plus a diesel car.”

The provisional BER assessment for the house also, remarkably, turned up ‘minus’ numbers for three of its key metrics — the primary energy demand, energy performance co-efficient (EPC) and carbon performance co-efficient (CPC). For example, while an EPC of less than 0.3 is needed for the house to comply with the nearly zero energy building standard in Ireland’s building regulations, assessor Jonathan O’Toole of OTE Solutions calculated a figure of - 0.334, indicative of the house’s superb thermal efficiency and self-sufficiency with on-site solar energy.

But forget all that for a minute. What is it like

CASE STUDY

to live in? Reynolds says that the house has been a big hit with the kids. Throughout the lockdown, they tended to gravitate towards the first-floor terrace, which you access through the kitchen and which operates as a kind of additional living room. “The one thing that gets me is the air quality. It’s like when you’re in Dublin and you go down the country.

You get that lovely fresh air that knocks you out and after a week, you get used to it.”

“It’s brilliant. It’s been a really positive, really interesting experience. I’d be very keen to do another one, I’d love to see if I can do something else with the next one.”

Mel Reynolds is currently selling the passive house plus mews house to fund his next project. For enquiries contact peter.kenny@ie.knightfrank.com.

WANT TO KNOW MORE? The digital version of this magazine includes access to exclusive galleries of architectural drawings.

The digital magazine is available to subscribers on www.passive.ie

SOUTH DUBLIN

SELECTED PROJECT DETAILS Client: Louise Reynolds Architect & project management: Mel Reynolds Contractor: Sean Regan Ltd Quantity surveyor: Damian Bowers & Associates Services engineer: Conlon Engineering Structural engineer: Carraig Consultants Passive house & thermal bridging consultant: Earth Cycle Technologies Energy conservation consultant: Tim Cooper Conservation Engineering Passive house certification: Mead Consulting BER: OTE Solutions Health & safety: Safety Solutions Roofing: KD Roofing Mechanical sub-contractor: MountainLodge Mechanical Services Electrical sub-contractor: Thomas Kenny & Co Ltd Masonry: Quinn Building Products External render: Baumit UK Airtightness tapes & membranes: Siga

Airtightness membrane (liquid): Blowerproof Ireland Flat roofing: Moy Materials Masonry thermal breaks: Foamglas Steelwork thermal breaks: Armadillo Noise & Vibration Ltd GGBS concrete: Kilsaran FSC certified timber: Glennons Insulation (various): Kingspan Insulation Internal blinds: Curtain Traders MVHR: Pichler, via VentHeat Solar PV: Solartricity PV diverter & EV charger: Myenergi Windows & doors: Internorm, via Eco Window Concepts Metal fabrication: Dunfab Engineering Sanitaryware: Bathhouse Kitchens: Nobilia, via Timbercraft Rooflights: Fakro Landscaping & living wall: SAP Landscapes Ironmongery: KCC Architectural Rainwater harvesting: Wastewater Solutions

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CASE STUDY

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CASE STUDY

SOUTH DUBLIN

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EMBODIED CO 2 A lifetime embodied CO2 calculation of Cove Mews by Tim Martel using the AECB’s PHribbon tool delivered some interesting findings and provides a clear lesson that life cycle assessment results need to be treated with care and considered in context.

The house scored a cradle to grave figure of 782.1 kgCO2e/m2 of the treated floor area (TFA), with 210 kgCO2e/m2 for the solar PV array alone – a figure which assumes the array would be replaced once within the projected 60 year life span in the calculation, and therefore doubles the associated embodied CO2 emissions.

Given its comparatively compact size – certainly in its current six person family configuration – it’s worth considering that a much larger version of the house would have scored a significantly lower result per square metre, even if the absolute tonnage of embodied CO2e (carbon dioxide equivalent) increased.

If the PV array is removed from the calculation, the score drops to 570 kgCO2e/ m2 TFA, which means it likely comfortably meets the RIBA 2030 embodied carbon target of 570 kgCO2e/m2 net internal area (NIA). According to Tim Martel TFA and NIA calculations tend to be very close.

But might a substantially larger version of this house, with no PV array and a pair of SUVs in the drive, meet the RIBA 2030 embodied CO2e targets, even though such a house may arguably be far more polluting?

Embodied CO2e emissions tend to be

calculated separately from a building’s operational energy use throughout its lifespan, meaning that in this case any extra embodied carbon invested in the high performance fabric and, in particular, the large PV array, are separated from the operational CO2e benefit they will deliver over time. That calculation isn’t simple, as grid electricity is on a trajectory of decarbonization.

If we believe the projections, grid electricity will be CO2 neutral in the UK by 2033 and in Ireland by 2040, with microgenerators like the PV array at Cove Mews playing a central role in an increasingly decentralized energy system.

This means there may be a self-defeating argument if the upfront embodied CO2e emissions of a PV array are found not to stack up due to future decarbonized electricity that they help to bring about.

The operational CO2e savings at Cove Mews are considerable based on current electricity emissions factors. The clever integration of a low energy house, PV array and electric vehicle were compared to a notional alternative posited by Tim Cooper and Mel Reynolds: a minimum compliant NZEB home, drawing more heavily on dirtier grid energy, combined with a fossil fuel powered car, which Cooper has calculated to emit 3.88 tonnes of CO2e per year, more than three tonnes higher than the projected figure for Cove Mews plus an EV, in both cases based on an average mileage of 15,000 km/yr.

EMBODIED CO2e Cradle to Grave

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CASE STUDY

SOUTH DUBLIN

IN DETAIL Building type: Detached 120 m2 externally insulated two-storey detached mews Location: Sandycove, Dún Laoghaire, Co Dublin Completion date: December 2019 Budget: Not disclosed Passive house certification: Passive House Plus certification in progress Space heating demand (PHPP): 15 kWh/m2/yr Heat load (PHPP): 11 W/m2 (Non-renewable) primary energy demand (PHPP): 75 kWh/m2/yr Primary energy renewable (PHPP): 58 kWh/m2/yr Heat loss form factor (PHPP): 4.29 Overheating (PHPP): 1.4% of year above 25C Number of occupants: 3 to 6 (design figure) BER: A1 ( - 60.30 W/m2K, provisional figure) Energy performance coefficient (EPC): - 0.334 (provisional) Carbon performance coefficient (CPC): - 0.317 (provisional) Environmental assessment method: Home Performance Index pending Estimated energy consumption: Using a maximum demand occupancy of six persons, Cove Mews would require 6,908 kWh (2,010 kg CO2) in total for all heating, hot water and consumer loads. Without thermal storage, it would export significant solar PV surplus to the grid of 4,550 kWh. When various demand/control options are deployed (water and battery storage) to optimise on-site renewable energy use, consumption of grid electricity reduces by two-thirds to 2,244 kWh (653 Kg CO2) and 976 kWh is exported to the grid. When an electric vehicle is then charged at the house, total use of grid electricity increases to just 3,008 kWh (875 kg CO2) for both house and car, assuming 15,000 Km mileage per year, and just 613

kWh is exported to the grid.

CO2: House and electric vehicle combined emit 875 kg CO2 per annum. For comparison, a typical NZEB A3 rated home with an efficient diesel car emits 3,882 kg CO2, over three tonnes more CO2 annually, based on current Irish CO2 intensity factors.

Energy bills (measured or estimated): Based on detailed demand-control model with occupancy of 6, annual bills for all energy consumption are estimated at €300.

Space heating and hot water account for €0 of this as these are fully met by the PV array. When electric vehicle (EV) charging is added, total imported energy costs rise to €393, which assumes 15,000 km for EV. Running costs are unit charges plus VAT, do not including standing charge or PSO levy. Assumes state-of-charge based smart charging of the EV. Airtightness: 0.57 air changes per hour at 50 Pascals Thermal bridging: Foamglas courses used in foundations to limit thermal bridging, Quinn Lite blockwork throughout with Compacfoam supports to window reveals (glazing positioned in external insulation zone), Alma-T to all thresholds below DPC level, Armadillo thermal-break pads to steel column connections. All service cavities filled with Metac insulation to reduce thermal looping.

Letterbox and drainage all external to building envelope and garage gate externally mounted with no connections to building.

Ground floor: 150 mm thick 50% GGBS reinforced concrete slab insulated with 270 mm Kingspan K3 insulation.

U-value: 0.1 W/m2K Walls generally: Acrylic external render externally on 140 mm Kingspan Kooltherm external wall insulation, on 215 mm Quinn Lite B5 blocks, on 12.5 mm plaster, on 15 mm dabs internally. U-value: 0.12 W/m2K North wall: Acrylic external render on 200 mm Kingspan Kooltherm external wall insulation, on 215 mm QuinLite B5 blocks, on 12.5 mm plaster, on 15 mm dabs internally.

U-value: 0.09 W/m2K Roof and upper deck: Paralon NT4 2 ply roofing membrane, on 120 mm Paratorch insulated board, on 18 mm OSB, on timber

joists with 15-90 mm Isover Metac mineral wool insulation on 210 mm infill Kingspan Kooltherm K7, on 15 mm OSB board to underside, on 25 mm service cavity, on 12.5 mm plasterboard. U-value: 0.1 W/m2K Undercroft Soffit (upper floor to external area below): Acrylic external render, on 200 mm Kingspan EWB insulation, on 15 mm OSB board, on timber joists with 300 mm Isover Metac mineral wool insulation to services zone and 210 mm interstitial Kingspan Kooltherm K7 insulation, on 15 mm OSB, on 10 mm cement board, on 20 mm ceramic tile finish over. U-value: 0.07 W/m2K Windows: Internorm triple glazed aluminiumclad oak windows, with argon filling and an overall U-value of 0.73 W/m2K; G value 0.6 Roof windows: 2 x Fakro DXW DW6 triple glazed flat roof ‘walk-on’ windows.

U-value: 0.7 W/m2K Heating & ventilation system: Pichler PKOM4 heat pump combi unit, Passive House Institute certified to have heat recovery rate of 85% (dry heat recovery 88%) supplying ventilation, space heating and hot water with 212 litre integral HW tank (av. storage tank temperature 45 C. Secondary water storage: Secondary 120 litre tank and 7 litre Quooker Combi independently heated from PV array.

Water: FLine Diver 5, 000 litre rainwater harvesting tank supplying all irrigation and WC. All sanitary fittings are low-flow 9 litres per min.

Electricity: 41 m2 (24 x 340 Wp) LG Neon solar photovoltaic array roof-mounted at KD-D-Dome system with average annual output of 6.8 kW, Solis inverter and Pylontec 4.8 kWh battery storage. MyEnergi Eddi diverter, MyEnergi Zappi smart EV charger and MyEnergi Hub. Green materials: 50% GGBS cement used in all insitu-concrete, aerated blockwork throughout with FSC certified timber in all areas. Biodiversity enhanced with the installation of ‘Living Wall’ and Acacia screen planting to upper level terrace along with mature specimen Magnolia at ground level.

All ground surfaces are permeable along with re-surfaced lane which is water permeable asphalt.

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INSIGHT

RADON

RADON

IN PASSIVE HOUSES Radon is one of the most dangerous indoor air pollutants, yet there is little research on how it is affected by different forms of construction and ventilation. A new study, however, suggests that homes built to the passive house standard are significantly less at risk of radon build-up.

Words by Kate de Selincourt

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ew research comparing radon levels in passive and non-passive homes suggests that passive house construction protects occupants from excessive radon levels.

Across Ireland, around one in 12 homes exceeds the level of 200 Bq/m3 (becquerels per cubic metre of air) above which remedial action is recommended. In a survey of 77 certified passive homes in the Republic of Ireland, and 20 in the UK and Northern Ireland, none exceeded this level.

The average radon level in the passive homes was less than half the average found in a sample of non-passive homes at the same locations. New build passive houses had the

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lowest radon levels, but the small subset of five Enerphit (passive retrofit) projects also had radon levels lower than non-passive homes.

The research was led by Barry McCarron of South West College, Enniskillen, and supervised by Dr Xianhai Meng and Professor Michael McGarry of Queens University Belfast. South West College has a particular interest in passive house performance. It is a leading centre of passive house training in Ireland, with its own passive house certified teaching and research space, the CREST centre.

In Ireland and the UK, radon is the leading cause of lung cancer after smoking, and is recognised as an important indoor pollutant

by both governments. It is a colourless, odourless and tasteless gas emitted from rocks and soil that can enter buildings through cracks and gaps, and accumulate to potentially dangerous levels.

In Ireland, it is estimated that radon exposure accounts for approximately 14% of all lung cancers – equating to around 300 cases per year. In the UK around 1,100 deaths from lung cancer each year are related to radon in the home.

Yet as Barry McCarron found, there is very little research anywhere looking at the impact of construction methods, as opposed to the impact of location, on building radon levels. The National Radon Control Strategy

INSIGHT

in Ireland notes that “the relationship, if any, between increased airtightness and elevated radon levels is unknown”. There has been speculation that airtight dwellings might be at risk of a build-up of radon.

Passive house ventilation is known to deliver excellent indoor air quality, on metrics such as relative humidity and carbon dioxide . But nonetheless Barry McCarron found that even some of his architecture school colleagues assumed that passive houses would be at higher risk from radon due to their airtightness. “When I was planning this research, I would get that typical question – oh, passive house couldn’t possibly be good for radon, could it?” he recalls.

Less radon in passive houses Of the 97 certified passive houses studied, 92 were new build, and five were Enerphit retrofits. Comparison homes in the immediate vicinity were found for 25 of the passive homes — these were of a similar size but of non-passive construction.

Radon monitoring showed the certified passive house dwellings performed a lot better in respect of indoor radon concentrations than the comparison dwellings, and compared to Irish homes as a whole. The average level in passive homes was 36 Bq/ m3, compared to the level in the comparison homes, which averaged 88 Bq/m3. The national average level in Ireland is 77 Bq/m3.

The Irish and UK governments have both set an ‘action level’ of radon gas concentration of 200 Bq/m3, above which remedial action to reduce indoor radon concentration should be

taken. In the UK there is also a ‘reference level’ of 100 Bq/m3, which according to the public health authorities, all homes should aim to be below.

None of the 97 passive house certified homes (new build and Enerphit) exceeded the action level of 200 Bq/m3, while two of the 25 comparison homes (8%) did so.

All but 7% of the passive homes were also below the lower ‘reference’ level of 100 Bq/m3, while 16% of the comparison homes exceeded this. In Ireland as a whole, an estimated 25% of homes are above 100 Bq/m3.

What about retrofit?

The average radon level in the five Enerphit homes was 72 Bq/m3, not as low as the new build passive homes, but still lower than the national average, and below the 100 Bq/m3 reference level.

There were 10 matched pairs of homes located in designated high radon risk areas.

Only one of the certified homes there (an Enerphit retrofit) exceeded 100 Bq/m3, with a recording of around 150 Bq/m3. However, the identical but non-retrofitted home next door had one of the highest radon levels measured in the survey, at over 400 Bq/ m3.

Although the numbers were too small to enable predictions about the radon performance of certified passive house retrofit more generally, these early results are encouraging signs on a potential benefit of the passive house approach. And they are particularly encouraging in the light of research from Germany suggesting non-passive house retrofit can make radon levels worse.

RADON

Like the new build passive homes, the Enerphit dwellings had new, airtight floors installed in order to meet the airtightness requirement of the standard. And as mandated by the standard, they all had balanced whole-house ventilation.

But research from Germany suggests that in retrofits where wall airtightness has increased but no ventilation is added, radon levels tend to rise.

Winfried Meyer from the Federal Office for Radiation Protection in Germany recorded radon levels in just over 100 buildings refurbished to improve energy efficiency, and compared them with nearby unrenovated buildings from the national radon database.

Out of 144 rooms in 122 refurbished houses, 33 (almost one in four) of the rooms exceeded the 100 Bq/m3 reference level. However only four of 144 rooms in unrenovated homes – closer to one in 40 – exceeded this level.

Radon concentrations of more than 300 Bq/ m3 were found in the living spaces of refurbished homes (five rooms), but in none of the unaltered houses.

The refurbished buildings commonly had new windows, and wall insulation (there was no information available about the floors).

But “these buildings do not have ventilation systems,” Winfried Meyer reports. “The exceptions are the temporary mechanical ventilation of bathrooms and WCs in a few buildings.”

As she writes: “The current energy saving regulation in Germany (EnEV‐2015) stipulates that buildings must be airtight. In most cases however, manual window ventilation is considered sufficient.”

The author also looked at radon levels in new passive house dwellings, and found that these were no higher than the national average.

This German dataset is not directly comparable with Irish and UK dwellings, as overall radon levels appear lower, and it is not possible to say whether this is a feature of the differences in construction and/or lifestyle, or even geology, between the countries. However, it does highlight a possible risk from retrofit when whole house ventilation, and possibly floor sealing, are not addressed.

Meyer concludes that “high radon levels in energy‐efficient houses are not inevitable...

They can be avoided by adequate user‐ independent air exchange and by limiting the amount of radon that enters the building.”

The role of ventilation A couple of small experiments have demonstrated how effectively mechanical ventilation with heat recovery [MVHR] can remove radon from a living space.

Ventilation consultant Ian Mawditt’s own home is in a radon risk area. The house is a low energy retrofit, featuring both highly airtight fabric and whole-house MVHR. Because of the radon risk, Mawditt has also installed a dedicated extract fan beneath the remaining suspended section of floor. (Suspended floors are generally not airtight, and the floor of

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INSIGHT

the undercroft can often be bare earth with no covering, though in this case there is a concrete slab over it).

To investigate the role of both systems, he tested the effect of turning them off. The MVHR flow was turned down from 0.4 to 0.1 air changes per hour for two weeks (during a short absence). This saw radon levels rise steeply. After two weeks the level reached around 600 Bq/m3, around ten times the base level. At this point the occupants returned and the MVHR was returned to normal running – which saw the radon clear equally rapidly.

Disabling the underfloor extract fan on a separate occasion also saw a rise in radon levels, although not as dramatic. The effect was again reversed when ventilation was re-instated.

In a new build passive house in a ‘high-radon’ area in Germany, a similar, if less dramatic effect was observed when ventilation was turned off: radon levels rose between three and seven fold.

What about the floor?

Alongside the ventilation, another notable feature of certified passive house and Enerphit homes is an airtight floor – necessary in order to achieve the airtightness targets of these standards. This is in contrast to most existing homes and many standard new ones, particularly in the UK. In Ireland, amended building regulations in 1998 required radon preventive measures in new buildings in designated high radon areas.

The UK building regulations also require radon protection in higher radon risk areas.

In the UK, public health research suggests the presence of a radon barrier does reduce radon levels, with 30% of homes without barriers in high-radon areas having levels of radon above 200 Bq/m3, while only 12% of those with a barrier do.

Similarly, Barry McCarron reports, the

Airtightness Level Comparison

21

ACH-1 @50pa

RADON

48

0

10

20

30

40

Average Radon Level - Bq/m <0.3 ACH

60

>0.3 ACH

Average radon levels in passive houses with airtightness less than 0.3 air changes per hour (ACH), versus passive houses greater than 0.3 ACH.

prevalence of above action-level homes in Ireland has decreased since the building regulations were amended. However, radon barriers alone do not guarantee safe radon levels, as the national databases confirm.

As Barry McCarron warns, these barriers are not always well installed. “It’s fiddly to install them correctly – the barrier needs to be taped in to preserve the airtight seal.

They are also vulnerable to damage before the slab is poured, if care is not being taken on site.” High radon levels have also been observed in homes outside the highest radon risk areas, where protection will not necessarily be mandated.

Although guidance suggests a radon barrier

should be installed in such a way as to prevent soil gas leakage into the dwelling, there are no specific installation checks.

An even greater concern is radon levels in existing buildings. Many existing homes in the UK and Ireland have suspended floors and no radon mitigation at all.

Barry McCarron’s research found a couple of existing homes with very high radon levels among the 25 that were sampled. “My sense is that some of our older stone houses are potentially at high risk of radon build-up,” he says.

While new dwellings have at least some purpose provided ventilation, older homes may have blocked chimneys, reasonably

Ceritifed Passive House Radon Montioring Results

Radon Level - Bq/m3

Seasonal Adjusted Average

Certified Passive House Sample Monitored radon levels from 97 passive houses in the study

60 | passivehouseplus.co.uk | issue 35

50

3

INSIGHT

RADON

Preston Springs (above), a new certified passive house, has much lower radon levels than the 1890s-built house right next door (below).

airtight fabric (possibly including replacement windows) but rely mainly on window opening for ventilation.

As was suggested in the research from Germany, energy retrofit may make this situation worse. Suspended floors are often retained unless a very comprehensive retrofit is being undertaken. But the walls, doors and roof may be made more airtight by installing new components, draught-proofing, and insulation.

Overall, these studies indicate that combining effective balanced ventilation with a sealed floor (incorporating radon protection if in a high-risk area) reduces radon risk. Both of these features come as standard in a certified passive house or Enerphit.

A complete airtight envelope, validated by testing, plus properly designed, installed and commissioned balanced ventilation, are the cornerstones of low energy construction and healthy and comfortable living conditions. They are crucial elements in a radon mitigation strategy, too. There seems little reason not to build, and retrofit, everything this way.

Radon at Preston Springs Preston Springs is a new passive house in Yorkshire designed by architect Mark Siddall. The â&#x20AC;&#x2DC;Radon in Homes in Englandâ&#x20AC;&#x2122; 2016 data report defined the average radon concentration for the Richmondshire district where it is situated as 100 Bq/m3.

Preston Springs recorded figures of just 30 Bq/m3 in the ground floor living room and 37 Bq/m3 in the upstairs bedroom.

The comparison building right next door, built circa 1890, has more elevated levels of 127 Bq/m3 on the ground floor and 108 Bq/m3 on the first floor, figures more in alignment with the Public Health England data for this postcode area. Overall the passive house radon level is 71% lower than the dwelling next door.

ph+ | radon insight | 61

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Marketplace News VIESSMANN LAUNCHES NEW COMPACT HEAT PUMP

Partel announces RIBA accredited airtightness CPD

P

artel, a leading specialist in high-performance building envelopes, is currently running a new RIBA-approved CPD programme titled ‘Best Practice for Air and Windtight Structures’.

The CPD focuses on the importance of air and wind-tightness in low-energy building design. It discusses the importance of external and internal membranes and their sealing, and highlights best practice on how to specify and install relevant products and components. It also focuses on the risks associated with airtight buildings, and how best to overcome these.

Highlights of the CPD include:

V

iessmann has introduced the new Vitocal 100-A air source heat pump, the most compact and affordable model in its range. Designed for ease of installation in the standard British heating system – and therefore ideal for the replacement of gas and oil boilers – the monobloc unit’s tight dimensions are perfect for homes where space is at a premium. Its A+++ rated energy efficiency will benefit end-users with low running costs, Viessmann said.

Viessmann UK’s managing director, Graham Russell, said: “The Vitocal 100-A is a new, environmentally-responsible heating option that is as simple to retrofit to existing homes as it is to specify for new builds. Viessmann is serious about offering a quality product in this volume sector of the market and therefore the Vitocal 100-A is price-competitive with equivalent standard monobloc air source heat pumps from other leading manufacturers.”

The Vitocal 100-A is a fully integrated outdoor unit that does not require a complementary indoor unit. The monobloc design means installers are not required to work on, or connect any, refrigerant-carrying parts; therefore, a refrigerant certificate is not required.

R32 refrigerant, which has a lower global warming potential than other conventional refrigerants, is used. Six versions of the heat pump are available, with outputs ranging from 6 to 16 kW. Where a greater output heating system is needed, such as in larger buildings, Vitocal 100-A units can be arranged in a cascade system of up to seven heat pumps. The heat pump can be installed to work in conjunction with an indoor-located, space-saving combi cylinder, which combines a 250-litre heating water buffer cylinder and 50-litre DHW cylinder, or with an outdoor-located plinth-style horizontal buffer store for additional space-saving inside the home.

The Vitocal 100-A heat pump achieves 60 C temperature at -5 C outside temperature and has a COP (coefficient of performance) of up to 4.9 (A7/W35). The Vitocal 100-A can be operated directly with its built-in control unit, which is easy to use and has a plain text display.

The Vitocal 100-A is available now in UK merchants. •

• • • • •

Correct product choice for specific scenarios Correct detailing and specification for optimum results How to determine where an airtight layer should be How to specify correct components for varying scenarios Airtight principles and associated risks

Partel’s ‘Best Practice for Air and Windtight Structures’ RIBA CPD will be held online for the rest of 2020 via Microsoft Teams. This is a unique opportunity for architects, engineers, and construction and design professionals to gain up-to-date knowledge on a range of innovative products and techniques, earn CPD points, and enhance their personal proficiency in airtightness. Being a RIBA approved CPD, attendees can also earn up to eight CPD points.

To book please e-mail contact@partel.com or visit www. partel.ie/cpd-and-training for more information. • (below) Partel’s CPD on best practice for air and wind-tightness is RIBA approved.

(above) The new Viessmann Vitocal 100-A air source heat pump.

ph+ | marketplace | 63

MARKETPLACE

PA S S I V E H O U S E +

Passive Building Structures delivers bespoke Manchester passive house L eading ICF building envelope specialist Passive Building Structures is currently on site completing a large new passive house in Didsbury, Manchester. The project offers a contemporary take on the surrounding traditional architecture.

The building, with a floor area just under 5,000 square feet over three floors, uses the full integrated Passive Building Structures system to meet passive house airtightness, U-values and thermal bridging requirements.

Floors, walls and roof all meet a U-value of 0.11. This includes an insulated raft foundation with two layers of 150 mm EPS, plus ICF walls which feature a 200 mm concrete core sandwiched between an inner layer of 108 mm EPS and an outer layer with 108 mm plus another 102 mm EPS. “Our rapid roof ultra-panel which consists of 300 mm EPS has also been engineered to eliminate any purlins or collar ties so promotes open plan living,” Pearce McKenna of Passive Building Structures told Passive House Plus.

The company also supplied and erected

internal load bearing ICF walls, while the house also features precast concrete floors and internal stairs on two floors.

There is also a 1.5 metre cantilever to the front elevation on the first floor, which had to be offset for protection of tree roots on site.

“This cantilever is incorporated into the building envelope and is fully insulated to ensure zero cold bridging,” McKenna said. “The cantilever has been designed with reinforced concrete beams integrated into the wall and insulated raft foundation.

This has eliminated the need for exposed structural steels.”

Passive house certified windows and MVHR will soon be installed at the project.

McKenna said the principal thing that sets Passive Building Structures apart from other ICF suppliers is that the company delivers a complete thermal building fabric on its projects.

“We have incorporated unique details into our system whereby all our components are interconnected/integral elements. Our system is poured monolithically from floor to floor.”

The company has particular experience in delivering bespoke high-end developments, such as architect Donn Ponninghaus’s RTE Home of the Year winning passive house in west Cork, which was previously featured in Passive House Plus.

For more information see www. passivebuildingstructures.com. You can also follow the Didsbury project on the company’s Instagram page (@pbs_icf). •

(below) The new passive house in Didsbury is built with the Passive Building Structures full building envelope system.

Ecological launch new airtight vapour boards E cological Building Systems have added FINSA superPan VapourStop passive house certified boards to their range of products. FINSA superPan VapourStop is an innovative wood particle board with a unique composition which differentiates it from other conventional boards on the market.

It features a high performance P5 inner chipboard layer, enclosed within two layers of high density woodfibre on either side, followed by a specialist airtightness film pre-applied on either side of the board.

This unique composition ensures superPan VapourStop fulfils three criteria within one panel: it provides a certified airtight barrier, the vapour control element prevents condensation build-up within the fabric of the building, and it offers high levels of structural stability for timber elements.

VapourStop has been used successfully on projects achieving passive house levels of airtightness and has been certified by the Passive House Institute to the highest airtightness category, pHA. All timber harvested for production is sourced from responsibly managed forests and the boards are also EPD certified. The Eurofins Institute conducted tests to determine VOC and formaldehyde emissions, and FINSA obtained a Class A+ by French standards.

Niall Crosson, group technical manager with Ecological, said: “We are delighted to partner with FINSA in the establishment

64 | passivehouseplus.co.uk | issue 35

MEMBRANE

BOARD CORE

WOOD FIBRE

Layer of chipboard with high moisture resistance resins, allowing its use in moist environments, up to Service class 2.

Layer of wood fibre providing excellent airtight qualities.

Special film on the two outer faces, providing the board with water vapour diffusion resistance.

COMPOSITION By pressing the layers together we achieve a synergy that provides the product great stability, high performance and high structural capacity.

FINSA superPan VapourStop, new to the Ecological Building Systems range

and exclusive supply of their range of innovative superPan boards in Ireland and the UK. The unique technical characteristics of the VapourStop board and its certification and environmental credentials make it the perfect partner for our range of innovative airtightness solutions.”

The product is classified as a P5 moisture resistant board, suitable for structural use, with omnidirectional resistance meaning it has equal resistance when applied in any

direction. “It is a very reliable substrate to screw and fix to with no breakout, and is very easy to cut with standard cuttings tools on site,” said Crosson. Further details and information can be accessed at www. ecologicalbuildingsystems.com.

Ecological also said they have experienced increased demand for their virtual CPDs, training courses and webinars which are available to book at www. ecologicalbuildingsystems.com/cpds. •

PA S S I V E H O U S E +

MARKETPLACE

WHY SHADING WILL BE CRITICAL IN THE AGE OF COVID Over the coming years there will be growing demand for openable windows in our office buildings to help prevent virus transmission — which is why high-quality solar shading will be more important than ever, says Smartlouvre managing director Andrew Cooper.

Smartlouvre’s MicroLouvre shading system consists of a fine bronze allow mesh.

T

he uptake of building certifications and accreditations that consider the wellbeing of occupants has proven that the building user’s comfort and contentment have been growing considerations for architects and building engineers in recent years.

For example, since its launch six years ago, the WELL Building Standard, which focuses on a building’s effect on health, is now being applied by 4,421 projects across 63 countries.

This includes both commercial and residential properties with the objective of advancing health, human experience and wellbeing through good design.

Without warning we find ourselves in a world completely turned around by a pandemic, where the wellbeing and safety of occupants has now become a key focus for all building owners and building service managers. It has been accepted that Covid-19 will not be eradicated anytime soon. It is changing the way we design the workplaces of the future.

Architects are currently altering building plans to accommodate CIBSE guidelines for increasing ventilation and introducing room cooling strategies that don’t rely on recirculating air conditioning systems.

At the same time, building owners and service managers of existing buildings are seeking ways in which to upgrade and retrofit to ensure that the risk of virus transmission is limited, whilst trying to provide occupant comfort and manage the risk of overheating.

With much of the world’s population working from home and for much of it ‘locked down’, we have been made very aware of the

impact our homes have on our wellbeing. We have improved our homes and gardens, for the benefit of our physical and mental health.

We have enjoyed the space, the safety, and the comfort of the homes we have created to our own personalised needs and wants.

This autumn, many of the world’s population face returning to the workplace after months at home, to spend nine-to-five in a building where our needs are not ‘personally’ met. Workplaces that may previously have provided comfort and familiarity are now changed by the pandemic.

Screens and other safety precautions have been introduced and soft furnishings removed or replaced so that we have only stark, wipe-clean surfaces to protect us from the risk of virus transmission. The visible changes to the workplace are immediately apparent. But the invisible changes like the lack of air conditioning or reduced air flow, could have even greater impact on workplace comfort and wellbeing.

Since the outbreak of coronavirus, the ventilation strategy of all shared spaces needs review. CIBSE’s advice is to increase ventilation as much as possible, increasing the flow of outside air and preventing any pockets of stagnant air.

Workplaces that lack good air quality, natural lighting or temperature control have a huge impact on workers’ energy and remove any chance of creative thinking.

More importantly, thermal comfort has a proven effect on our ability to make good decisions and even on taking risks with our safety. For example, people might not wear

personal protective equipment properly in hot environments.

As well as being a key option for limiting virus transmission, increasing air movement by introducing natural ventilation can also help to control thermal comfort. Furthermore, directing the fresh air upwards allows for displacement of hot indoor air that has risen to the ceiling, with cooler air from outside to further reduce the indoor temperature.

Wherever possible we need to increase the amount of indoor air that is replaced by outdoor air. Operable windows are all too often taken for granted in office buildings, and their importance overlooked.

Natural ventilation will play an important role in the future of our buildings, along with mechanical ventilation using fresh air, both for limiting the risk of virus transmission but also for reducing energy consumption, carbon emissions, and building running costs. However, with the benefits of open windows comes the need to manage heat and glare. Internal blind systems remove visibility out and a connection with the outside world, and only protect the room from a minimal amount of heat gain. External shading systems do work but are expensive to install and maintain as well as reducing the quantity and quality of daylight and vision out.

Smartlouvre’s MicroLouvre product, designed as a solar shading window screen, consists of a fine bronze allow mesh, comprising 700 tiny ‘bris-soleil’ fins per metre of fabric, measuring only 1.5 mm in depth. It is installed on a frame external to any windows, allowing heat to accumulate on the surface of the metal and then dissipate to the outside before it reaches the window. The heat is blocked before it hits the glass, by a metal fabric, with micro fine louvres woven in to dissipate the sun’s heat and energy but not block natural daylight, natural ventilation or vision out.

The louvres are micro fine, and angled at a level to ensure optimum light in, and visibility out, whilst protecting building occupants from the heat, glare and even external viewing in. It’s known as angular selective technology.

The 80% open area and angle of the louvres allow natural ventilation in a laminar flow with a distinct upward trend, directing the outdoor air towards the ceiling inside the building.

With its passive, angle selective, maintenance free technology, MicroLouvre supports all today’s energy saving, occupancy comfort and sustainable building performance requirements. To find out more about MicroLouvre go to www.smartlouvre.com. •

ph+ | marketplace | 65

T O BY C A M B R AY

COLUMN

The condensation myth Condensation within the structure of buildings is a lot more complex than condensation in a sweaty pub on a Friday night, writes building physics expert Toby Cambray.

I

n lieu of the real thing, I invite you to join me in an imaginary trip to a packed pub on a Friday evening. If convenient may I suggest The Crown, Cricklewood, whence we may return to discuss building physics on subsequent occasions. The tribute band are on the stage and several tipsy people are dancing away, sweating profusely.

The windows are closed in an attempt to keep the noise in and the wind out. You order a bottle from the fridge, and as you hand over your cash, droplets of water condense on the cold, impervious surface of bottle.

Condensation, in the sense that most people understand the term, is pretty rare in buildings. You might be surprised to hear that as a specialist in moisture risk, I don’t often worry about it (at least not with respect to this popular definition).

A simple definition of condensation is moisture forming into liquid drops when warm moist air hits a cold surface. This is more an observation than a definition and doesn’t tell the whole story.

A building can in principle go mouldy without ever experiencing condensation.

Air can hold a certain amount of water vapour, but that amount varies with temperature. Warmer air can hold more, colder air less. Relative humidity (RH) is the degree to which this carrying capacity is used. If you take some moist air and cool it down, the absolute amount of moisture doesn’t change but the RH goes up; cool it enough and you’ll get to 100%, at which point the moisture will form a liquid wherever’s convenient.

A more thorough definition considers the matter in terms of vapour pressure. Vapour pressure is a tricky concept. Another name for vapour pressure is partial pressure, which means the fraction of pressure in air (or another mixture) due to water vapour or another gas.

So at one atmosphere of pressure, water vapour might be ‘responsible’ for say 2.3 % of that total pressure, and therefore have a partial or vapour pressure of 0.023 atm or about 2,300 Pa, which happens to be the saturation vapour

66 | passivehouseplus.co.uk | issue 35

pressure of air at 20 C. If you try to add more moisture to the air under these conditions, it will condense out as liquid.

The term condensation is probably most often abused when it’s immediately preceded by the word ‘interstitial’. I will not discuss the pros and cons of the Glaser method or EN 13788 here but would encourage you to read about this if you have not done so already. This approach is based on the concept of vapour flux, analogous to the more intuitive heat flux. Apply a higher temperature (or vapour pressure) to one side of a material, and heat (or water vapour) will diffuse though it at a rate dictated by the resistivity of the material and its thickness.

It’s essential to differentiate between this process and the movement of bulk air around or through a material – this is also important and often problematic, but it is fundamentally different to diffusion. Therefore the simple ‘cooling air down’ definition doesn’t help here, and we must think in terms of vapour pressure.

If vapour (or heat) is diffusing through a wall, driven by a vapour pressure (or temperature) differential, and it encounters a higher resistance – a piece of glass say (or insulation in the analogy), there is a pile-up.

There’s still the differential, so the vapour or heat ‘wants’ to move from one side to the other, but it gets stuck.

At this interface the vapour pressure increases as more vapour tries to move through, until the vapour pressure at the interface approaches that inside, reducing and ultimately (in theory) cancelling out the vapour pressure differential.

But if this location is cooler than inside, because of some insulation, the vapour pressure can exceed the local saturation pressure before it cancels out the pressure to the inside, and water will condense out of the air onto the most convenient nearby thing.

This is why conventional design would have us avoid putting impervious (highly vapour resistant) barriers on the cold side of our insulation. A common and not entirely correct secondary conclusion is that we should instead, always have something impervious on the warm side of the insulation. I agree with the first statement to a much greater degree than the second one.

So now we have an understanding of ‘classical’ condensation and its interstitial variety. Why would I say that I don’t generally concern myself about it? Well, for one thing there’s enough understanding out there to

avoid this in most cases. I can of course provide an ‘interstitial check’ if you insist on calling it that, but the sort of problems I’m usually asked to investigate are much more interesting.

As a very general rule of thumb, mould growth can initiate at about 80% RH, and timber decay at 95% or so. Convention suggests that 80 and 95 are less than 100, indicating that a building can in principle go mouldy and rot away without ever experiencing a drop of condensation.

Finally, and most complex is the reason (or rather one of them) that also renders EN 13788 unsuitable in many circumstances. Porous materials exhibit much, much more complex behaviour with respect to moisture than the idealised materials mentioned above. Solid metals, sheet glass and many membrane products for example can be reasonably accurately represented in simple terms, but the majority of materials we build with cannot, to a greater or lesser degree. This is because they are somewhat porous, and somewhat hygroscopic.

Hygroscopic materials have an affinity for moisture, which will bind to them across the spectrum of relative humidity. This means that as vapour pressure increases, these materials will absorb moisture, moderating the increase in humidity.

If materials such as brick and plaster are present under these conditions they will more often than not absorb moisture fast enough to avoid condensation as you might see on the side of your beer bottle. Students of building physics may (correctly) point out that there is indeed condensation of a different type – capillary condensation, but this is a more complex process than this column allows (being based on the ‘lies to children’ type of simplifications necessary to meet the word count).

So as with many things, when it comes to condensation in real buildings, I must deploy one of my most over-used expressions, or simply point to the phrase on my T-shirt: I think you’ll find its more complicated than that. n

Toby Cambray is a founding director at Greengauge and leads the building physics team. He is an engineer intrigued by how buildings work and how they fail, and uses a variety of methods to understand these processes.

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