Insulation & Airtightness - Autumn 2021

Guide Selfbuild

INSULATION & AIRTIGHTNESS GUIDE

100 DEFINITIONS

119

THE NZEB NEW BUILD

108

AIRTIGHTNESS SYSTEMS

106

INSULATIONS TYPES

98 OVERVIEW / 112 INSTALLATION 116 NEW BUILD ENERGY STRATEGIES / 122 ECO INSULATED NEW BUILD 124 RETROFIT STRATEGIES / 128 NZEB ENERGY UPGRADE

AU TU MN 202 1 / SE L F B U IL D / 9 7

INSULATION & AIRTIGHTNESS GUIDE / OVERVIEW

Strategic thinking Your airtightness and insulation strategy will depend on how you build your house, what your overall aim is for energy efficiency, and how you plan to ventilate it. You will then have to make choices based on cost versus performance versus eco credentials.

image: Freepik.com

9 8 / S E L F BU IL D / A U TU MN 2 0 2 1

Guide Selfbuild

he adage “Build Tight, Ventilate Right”, coined by Earle Perera of the Building Research Establishment in the 1990s, is as true today as it ever has been. This means that in energy efficient buildings, the insulation and airtightness strategy must factor in ventilation to protect your own health and to prevent sick building syndrome. But there’s even more to it than that, writes Patrick Waterfield.

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Dr Patrick Waterfield is an energy consultant based in Belfast.

Victorian buildings were very robust, adaptable and abundant in architectural features. They had large areas of glazing and plentiful ventilation due to their lack of airtightness and fireplaces in most rooms. This meant ample fresh air and light, but also poor energy/resource efficiency.

The challenge today is to retain the positive features, including an efficient ventilation strategy (which was in many cases sacrificed in the late 20th Century to make way for insulation), while addressing the downsides. Here are some of the variables to consider: Lifecycle costing: While the precise definition can vary, it tends to take into account the upfront cost (and, in the case of insulation for example, payback period in terms of energy saved against purchase price), what you need to pay to maintain and replace the product as you use it, plus the cost of disposal of materials at end of life, all of which is adjusted for inflation.

Embodied energy: This analysis not only looks at the energy a building will use during its lifetime, but at the energy consumed in the extraction/ processing/manufacture of components and, potentially, the recyclability of materials at end of life. Databases are available for the embodied energy of materials, which are generally independent

of geographical location. An extension of this approach is embodied carbon assessment, a trickier and less researched subject as it depends on the energy types used for extraction, manufacture and shipping of materials/components and will thus vary depending on where the products are produced and where they are used.

Eco credentials: It is possibly simpler to only look at the inherent eco credentials of a material: Does it need much processing and what impact does its extraction have on the environment? Can it be readily recycled or reused at end of its life? As far as I am aware, there are no specific eco options for airtightness and vapour control membranes – these are engineered products with particular properties regarding air and moisture transfer in specific directions (into or out of the fabric). So the eco analysis tends to apply to insulation products, and herein lies the dilemma: the best energy performing insulation materials are usually the most engineered.

Overall, an insulation and airtightness strategy will need to take into account these but other performance related issues.

Moisture management comes to mind; for example a material that can help regulate moisture transfer will be suitable next to a

breathable membrane. There are dangers too in using impermeable materials in old solid walled houses as moisture movement needs to occur in the fabric.

When considering my own self-build nearly 15 years ago, I was often torn between using higher performing, oil based (plastic) insulation products and more natural materials with higher thermal conductance (poorer performance).

The rule of thumb is that lower performing insulation materials require greater thicknesses to achieve a given insulating effect.

And while happy to embrace a wider-than-normal wall element, I had to draw the line somewhere.

To give you some context, the driving force for my build was to design out the central heating system. I had calculated that I should be able to do that if I could reach an average U-value for the entire building fabric (including windows) of about 0.2 W/sqmK. Anywhere there was a breathable membrane I used hemp batts for their good moisture regulation properties. Then for the roof, the 200mm rafters were filled with 150mm PIR boards.

The floor had 200mm PIR insulation partly because it had to play a role in supporting the screed.

The 150mm timber stud walls contained mineral fibre, as per the standard make up for timber frame. The walls were then internally drylined with insulated

plasterboard (phenolic or PIR).

The windows were almost all triple glazed including rooflights.

And, as you would expect, the house has a mechanical ventilation heat recovery (MVHR) system. The q50 air permeability was 1.3 m3/ (h.sqm) which, though some way off the Passivhaus minimum requirement, I was happy with.

The whole house is heated by a wood burning stove with its own dedicated combustion air, assisted by the MVHR in distributing the heat around the house. The wood burner has a back boiler which feeds the hot water tank via a gravity loop.

Between the back boiler and solar thermal tubes (both feed the hot water tank), which complement each other well seasonally, the electric immersion has hardly ever been used (but there is an electric shower in the upstairs bathroom).

Today the house, which achieved an A2 energy rating at the time, performs as well as ever.

I have replaced the wood burner once (very recently) and the MVHR thermal wheel motor once (some time ago; I have also been changing the filters regularly of course). Otherwise we have used only logs for heating, at a cost of about €300/yr, and electricity for everything else, using approximately 2,500 kWh/yr.

A U T U M N 2 0 21 / S E L FB UI L D / 99

INSULATION AND AIRTIGHTNESS GUIDE / DEFINITIONS

A snug fit When building your house or carrying out a home improvement project, you will hear a lot about insulation and airtightness. But what are they and why do you need to know about them?

What’s the difference between an NZEB and a passive house?

and floor The walls, roof along with of your home, such as any openings doors are windows and ed to as together referr lope or ve en the building . building fabric

1 0 0 / SE LF BUILD / AU T U MN 2021

The terms passive house and Nearly Zero Energy Building (NZEB) both refer to designing buildings that require very little energy to run comfortably, i.e. low energy bills.

In the context of house building, a big difference is that NZEB is specifically referred to in Part L of the ROI building regulations, defined as a building with a very high energy performance that gets the very low amount of energy it still requires mostly from renewable sources, on site or nearby.

In practice, this means building a house that retains heat very well and installing some form of renewable system(s), usually in the form of a heat pump or solar panels.

Most designers will use the

term passive to refer to the German PassivHaus Institute’s definition of a passive house, which is again all about hitting minimum energy targets based on the building fabric. The PassivHaus Planning Package (PHPP) was the first low energy homes design software that really took off in Ireland, and was in widespread use well before the ROI building regulations introduced the NZEB requirement.

The basic premise is that the home is designed to be so airtight and well insulated that your space heating demand will be very low, i.e. no more than 15kWh/sqm/yr for a new build or 25kWh/sqm/yr for a refurb. The German PassivHaus standard also includes mechnical ventilation with heat recovery as a requirement, but there is no mandatory renewable component although you can of course include renewables in the PHPP design software.

Guide Selfbuild

Complied by Astrid Madsen, additional information from Patrick Waterfield

What is airtightness?

Airtightness is the ability of a system to prevent air leakage.

Air leakage is driven by pressure differences across the building envelope.

Too much air leakage, and your heating bills will suffer due to the draughts. Important too is the fact that air leaks can lead to fabric decay due to dampness.

The less air leakage the better, but it is important that there is adequate and controlled air circulating in the building to provide good indoor air quality for the occupants.

The airtightness barrier can be integral to the material, e.g. spray foam insulation or even plaster, or can be added on with a membrane. Airtightness and vapour control membranes are placed on the warm side of the insulation to avoid condensation in the fabric (see Watchpoints below).

They are joined with proprietary tapes. Paint on airtightness barriers are also available.

Not all membranes are the same and need to be specified for the particular application.

The most common measure of airtightness is air permeability, referred to as q50, in m3/h.sqmK at a pressure of 50 Pascals.

This is the measure used in the Building Regulations in ROI and in NI. Air Changes per Hour (or ACH, also referred to as n50) are based on the volume of the building instead of the envelope area. ACH are often quoted to demonstrate the airtightness of a building, but this is not the measure used by the building regulations.

The Passive House standard specifies ACH in their methodology; remember that this is a voluntary standard and even if you design to this benchmark with their planning package

(PHPP), you must separately prove compliance with the Building Regulation requirements with DEAP in ROI and SAP in NI. In most cases you will need to pay for an air permeability test to prove compliance (see p108).

What is insulation?

In the context of house building, insulation products are designed to reduce the rate of heat transfer across the building fabric.

Insulation limits the flow of heat energy between two environments that have different temperatures. So you will equally find insulation products around pipework and hot water cylinders to limit heat loss from your hot water, but also integrated within preinsulated products so as to prevent thermal bridging (see Watchpoints below), e.g. preinsulated steel or preinsulated window sills. Insulation can equally be integrated within the structure of the house.

How well an insulation product does its job is measured by its thermal conductivity. See p106.

The amount of heat you gain from the sun, through glazing, is known as solar gain. A well insulated house will retain this heat.

How much insulation is the right amount?

The main reason to insulate is to prevent heat from transferring from the inside to the outside, and vice versa, to save on your energy bills.

Unfortunately it is not a simple matter of increasing insulation thickness and getting the same

increase in performance. This is only true up to a point and it is where you will start weighing in the cost of adding more insulation.

There is an optimum thickness for each type of construction based upon not just the performance of the material, but also the space available in the wall, roof or floor. Once this has been determined go for the best (i.e. lowest) possible U-value within reasonable cost.

The U-value is the metric that shows you how well insulated your house is. It takes into account the entire build up of the wall, from the plaster/ plasterboard to the external finish.

In technical terms it

Watchpoints

calculates the combined thermal conductivity of all the components, and thickness of each, to give you a measure of how well the building element reduces the exchange of heat between two environments at different temperatures.

The lower the overall U-value, the better the build-up is at keeping the heat in. Insulation is what most reduces this number.

(say a cold external wall) and a warm part of your building fabric (say an insulated internal wall).

The build up of water, which will be hidden behind the wall, roof or floor, can then lead to fabric decay and mould growth. Vapour control management is the way to prevent interstitial condensation, which is why your airtightness strategy is so important.

The Building Research Establishment (BRE) defines a

When putting together your construction drawings, which will specifically put on paper how to build your floor, walls and roof, your architectural designer should take into account two common pitfalls: interstitial condensation, and thermal bridging.

Eliminating or minimising both is a requirement of the building regulations.

As you’ll have noticed on a single glazed window, where cold air hits a warm surface water droplets form. This is known as condensation. Interstitial condensation is when the same thing happens between a cold

‘Any weak link in your insulation and airtightness envelope will have a potentially significant knock-on effect on the overall energy performance of the house...’

AU TU MN 2021 / SE L F B U IL D / 1 0 1

ADVIE06_SB_v1

© GettyI mages

END OF THE BALANCING ACT

THE FIRST NSAI CERTIFIED DEMAND CONTROLLED VENTILATION SYSTEM Ventilation doesn’t have to be a balancing act. Aereco has achieved Ireland’s first Agrément certification for Demand Controlled Ventilation.

A system that self balances and automatically adjusts to the needs of a home, securing indoor air quality and energy savings.

The National Standards Authority of Ireland (NSAI) Agrément provides a pathway that has significantly simplified the commissioning and validation process of Aereco systems.

Aereco is committed to constantly innovating and improving the performance of their systems. Along with the recent release of their control indicator as part of the updated regulations for Part F, Aereco is reaffirming this commitment.

For more information: www.aereco.ie air on demand

Guide Selfbuild

thermal bridge, also called a cold bridge, as an area of a building construction which has a significantly higher heat transfer than the materials surrounding it. In places like Ireland, this can result in additional heat loss at these points.

This often happens where there is a break in the insulation (e.g. there are gaps in insulation due to poor installation), less insulation (e.g. it has been cut through to make room for pipework or other element), or the insulation is penetrated by an element with a higher thermal conductivity (e.g. in the case of a supporting steel beam).

A relative thermal bridge may also occur around openings due to a reduced thickness of insulation – to minimise this requires good details on the part of the architect, as well as good detailing on the part of the installer.

To estimate the heat loss at junctions in new dwellings, you will see reference to the Y-value, derived from the total thermal bridge losses. The lower the Y-value, the better.

Why you need an energy assessment

Integral to the design stage, whether new build or renovation, will be your energy strategy. This will dictate how much insulation you will be putting in and what level of airtightness you are aiming for.

The house’s shape and height will be two determining factors, as well as how much glass you plan to use. Insulated walls are much more efficient at retaining heat than windows can ever be, so a design with a lot of glazing will need to compensate with higher levels of insulation.

At the minimum, to do the energy calculations, you will need the input of a Building Energy Rating assessor (in ROI, list of accredited assessors ndber.seai.ie) or an Energy Performance Certificate assessor (in NI, list of accredited assessors epcregister.com).

In a new build, they will check if the house design that you have complies, on paper, with the energy requirements of the building regulations.

This is a crucial step. Building a house that doesn’t comply with the regulations will lead to costly remedial work down the line, so a provisional energy rating is necessary in ROI. Your provisional calculations must be uploaded when you file for your commencement notice, as they will prove compliance with Part L of the building regulations.

In NI, Building Control will ask for your design stage SAP assessment so even though the regulations are less stringent, you will still need to prove that your design complies and therefore get an energy assessment.

In a renovation project, an energy assessment will guide you on what upgrades are best suited to your property. Each building is unique, not only in its shape, size and year of construction but also because of the alterations that have been made over the years, potentially even including insulation upgrades.

The energy strategy must be tailored to the specific building.

What are the regulations?

Minimum insulation and airtightness requirements are outlined in Part L (ROI) and Technical Booklet F1 (NI) of the building regulations for both new builds and renovations (only major renovations in the case of ROI).

Each element, be it a wall or window, must meet minimum standards (i.e. maximum permitted U-values); airtightness is measured as a whole but any leak in one area will lead to a considerably lower result overall.

In relation to ventilation (Part F in ROI, Technical Booklet K in NI) the key aim is to provide sufficient clean fresh air for the occupants. This means minimising the risk of condensation, mould growth or other indoor air quality problems by ensuring a minimum number of air changes. Filters can be added to mechanised systems

What is an energy rating?

Energy ratings exist throughout Europe and consist of a certificate that gives your house a grade, on an A to G scale, much like your washing machine or fridge (A being the best).

In ROI they’re called Building Energy Ratings (BER) and in NI, Energy Performance Certificates (EPC).

Similar methodologies (in NI Standard Assessment Procedure or SAP, in ROI Dwelling Energy Assessment Procedure or DEAP) are used to prove compliance with the energy efficiency requirements of the Building Regulations and to draw up energy ratings.

You must carry out an energy rating before you move into your newly built home. In ROI, in the case of a renovation project, you need a before and after energy rating to get your grant from the Sustainable Energy Authority of Ireland (SEAI).

Information compiled by Astrid Madsen

A U T U M N 2 0 2 1 / S E L FB UI L D / 103

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Guide Selfbuild

to increase the air quality even further.

There’s also Part J in ROI, Technical Booklet L in NI, which are critical in relation to the supply of air for combustion appliances in a safe and efficient manner.

What is thermal imaging?

Thermal imaging are images that show different rates of heat loss from a building. This thermogram can thus highlight areas of air leakage. The cold air entering the house is shown on the image as shades of blue, indicating a draught.

A simpler way for detecting and visualising their presence is by using what’s known as a smoke pencil. Both professionals and DIY experts use these. They can quickly detect air gaps in discrete areas around buildings by following the smoke paths.

Build tight, ventilate right.

Current thinking has it that to save on your utility bills you should aim to achieve a high level of insulation and

airtightness. But as ‘build tight, ventilate right’ implies, you will also need a well designed and well managed process for introducing fresh air and removing harmful household contaminants. Otherwise your home could become a health hazard. We do, after all, spend over 90 per cent of our time indoors.

It’s important to note that any type of building, airtight or not, must be well ventilated to keep the air quality level high. A well

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managed airflow, not draughts, is the best way of ensuring that we live and breathe fresh air within our homes.

Airtightness is particularly important where heat recovery Thermal image showing a cold bridge (heat escaping in red) ventilation is installed, as the between balcony and wall system relies on being able to circulate air around the house regulations traditionally only and recover most of the heat content of the waste air to warm control only air quantity, not air quality. up incoming fresh air.

If the building is leaky, either or both of two things may happen – some of the warm air may be lost before its heat can be etely recovered – or ed for a compl ve gn si de e er w cold air may Open fires hile they ga d mindset. W come into different era an diant heat, 90 per cent of us ra the building imney. And out tremendo ped up the ch without being ca es gy er en cy story. this warmed up lf the inefficien tional 90 ha ly on ’s at th addi first. Either can extract an at because A roaring fire he r he outcome will ot s ilding’ per cent of a bu we didn’t previously reduce the was of something effectiveness en if its effect and efficiency of understand, ev y the passive the system. known, namel stack effect.

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A U T U M N 2 0 2 1 / S E L FB UI L D / 105

INSULATION AND AIRTIGHTNESS GUIDE / INSULATION TYPES

Insulation types There’s a lot of choice when it comes to insulation products; here’s what’s on the menu.

EPS beads

Rolls or batts?

The most common types of insulation can be categorised as being in rigid or roll form. The rigid forms tend to be boards used for walls, floors and as the backing on insulated plasterboard (the latter often PIR or phenolic foam), and those in roll form are more commonly used on the plane in roof spaces.

In roll form, mineral wool is generally considered the most cost effective and is made from molten glass, (glass wool) or stone (stone wool with superior acoustic qualities), spun into fibres.

For the same thickness you will however get less insulation effect from mineral wool than rigid boards made of plastic compounds, which include the polystyrene and phenolic families.

Plastic family

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10 6 / S E L FB U IL D / A U TU MN 2 0 2 1

Expanded polystyrene (EPS) can be formed into batts but also comes in bead form, which is a common way to insulate cavity walls by pumping them between the inner and outer leaf.

EPS is made with trapped air in beads and has a thermal conductivity in the same range as sheep and mineral wool with some modified types achieving better values. The incorporation of minute particles of graphite throughout the polystyrene gives a performance that is 15 to 20 per cent higher.

Extruded polystyrene (XPS) is formed by forcing the polystyrene through a die which closes the cells and is thus denser than EPS, with better insulation values.

Polyurethane (PUR) and polyisocyanurate (PIR), meanwhile, are either sprayed on or come in boards, and are made with a blowing agent. The outlawing of ozone-depleting gases meant that other blowing agents needed to be found and

Rigid board insulation

most manufacturers now use pentane or carbon dioxide.

Phenolic insulants are normally produced in rigid board form and are amongst the best insulators because of their fine cell structure.

Foil insulation is less commonly used, and most certified products require that it be used alongside other insulation types such as PIR.

Eco insulation

Due to the pandemic, with people spending more time than ever in their houses, indoor air quality is on everyone’s mind and products that help regulate moisture and do not emit volatile organic compounds are gaining favour.

Lifecycle analyses also tend to rank eco insulation products well, especially where they come from recycled sources.

The eco alternatives to the more mainstream plastic insulation products include sheep’s wool, recycled newspaper (cellulose fibre) and wood fibre.

These are often treated with inorganic salts, (usually boron), to provide resistance to fire, rot and

Guide Selfbuild

Complied by Astrid Madsen, additional information from Patrick Waterfield

The formula U-values, as seen previously, take into account every element of the wall, floor or roof build-up (as well as windows and doors) to rank how much heat is transferred from inside to outside.

The U-value is the inverse of the R-value or thermal resistance, so U-value = 1/R-value.

The R-value multiples the amount of the stuff you are using (thickness in meters) by the thermal conductivity (how inherently insulating the material is in W/mK). The inverse of all of the R-values added up will give you the overall U-value.

Rockwool, rockwool.ie

Roll insulation

pests.

Sheep’s wool comes in roll form, cellulose fibre either loose fill or in flexible batts, while wood fibre comes in rigid boards or flexible mats. Calcium silicate boards are most common for period properties and can be installed on the walls directly.

Hemp can be mixed with lime to make walls and plaster, cork can be used with clay for plasters or in batt form. Hemp is also available in semi rigid boards, pre-cast blocks and as part of proprietary eco building systems.

Practical considerations

Shrinkage, compaction: Some products will sag or shrink with time depending on the application; as a rule of thumb this is more common for rolled insulation. It is also very important that blown insulation is evenly distributed within a cavity wall so that no voids are left, though some settling of certain products may occur over time anyway, especially due to vibration (e.g. from heavy traffic).

Moisture: Allowing moisture to pass through the building fabric is part and parcel of the airtightness strategy but insulation should never get wet and if the house is correctly specified and built, it never will.

The main risk area is in cavity walls – rigid board can be installed maintaining a minimal cavity at the outer face of the insulation, while bonded beads are moisture resistant and allow water to be shed downwards between the beads. In exposed locations, with a high driving rain index, consideration should

Thermal conductivity W/mK (lower the number, the better)

Vapour Relative permeable cost (allows water (estimate) to pass)

Aerogel

0.014

Yes

++++

Phenolic foam board

0.02

No

+++

PIR/PUR boards

0.023

No

++

Mineral wool (stone) batts or roll

0.032

Yes

++

XPS boards

0.033

No

++

EPS boards or beads

0.034

No

+

Mineral wool (glass) batts or rolls 0.035

Yes

+

Cellulose spray/blown

0.035

Yes

++

Wood fibre boards

0.038

Yes

+++

Sheep’s wool batts or rolls

0.038

Yes

+++

Hemp batts or rolls

0.039

Yes

+++

Polyurethane foam (open cell) spray

0.039

Yes

++

Straw bales or boards

0.08

Yes

++

be given to a weatherproof outer layer (e.g. render), especially where cavities are fully filled.

DIY installation: All insulation products require care and attention to ensure there are

no gaps between the boards/ rolls. Some require specialist installation, such as spray foam, EPS beads, or blown fibre, but most others can be done on a DIY basis after some basic training.

A U T U M N 2 0 2 1 / S E L FB UI L D / 107

INSULATION AND AIRTIGHTNESS GUIDE / AIRTIGHTNESS SYSTEMS

Airtightness systems and testing According to the UK Building Research Establishment, a house built to be reasonably airtight and to the current ROI building regulations (5 cubic meters/h/sqm at 50Pa) consumes 40 per cent less energy than a house built to the old building regulation standard of 10 cubic meters/h/sqm.

10 8 / S E L FB U IL D / A U TU MN 2 0 2 1

You’ve been told many times about the need to insulate your home to a high standard. This is indeed by far the most cost effective way to lower your fuel bills, not to mention comply with the energy requirements of the building regulations. But insulation and airtightness go hand in hand.

Indeed after the insulation is fitted, an airtight membrane/ vapour control layer must be applied to the warm side of the insulation, otherwise all the hard work you put into insulating and protecting your home will literally leak at the seams.

Airtightness, or air flow and vapour control, (a term that takes into account the risk of condensation as well as the air exchange rate), is often associated with highly energy efficient homes. But that’s not always the case. In fact you can make your house airtight with natural ventilation.

With regards to the building regulations, it doesn’t matter which ventilation system you choose because during the airtightness test all of the vents, extracts (be they mechanical ventilation, trickle vents, passive stack, etc.) and chimneys are required to be sealed.

Where there is no mechanical ventilation, the wall vents are the only means of moisture management and may not be enough to manage moisture that you will be creating from living in the house. The building regulations take into account both ventilation and airtightness to determine how many vents you will need to keep the building ventilated. Too large a number of vents will cause draughts.

So if you are only relying on trickle vents for ventilation, it is good practice to open your windows to the front and rear of the home for 30 minutes two

to three times a day as this will clear moisture from the building.

This practice has been well tried and tested in countries such as Germany and Switzerland.

But as seen in the previous edition’s Systems Guide, Nearly Zero Energy homes and the ROI building regulations almost make mechanical ventilation a de facto requirement.

Construction drawings

The first step is to take pen to paper. Get the plans of your building and place a pen at a start point of your choosing (internally on the section) and then draw a continuous line around the entire building where you will have a continuous airtight envelope.

Any potential air leaks are when you have to pick your pen up from the paper, and as you may have guessed, particularly prevalent areas for air leakage are dormer windows, roof lights, windows, doors, junctions between floors and walls, loft hatches, etc. The rules for creating airtight seals at such junctions are as follows.

When the membrane meets a block wall (at a gable end for example) you will need to use a proprietary mastic to seal the edge of the membrane to the blockwork. It is important to emphasise that standard cavity blockwork is not airtight until it is plastered. Therefore it is recommended that the blockwork is plastered with a scratch coat prior to using the mastic. Continue the scratch coat right down to where the block meets the floor, even where it will be covered by skirting, as the skirting itself will not be draught proof.

Where the membrane overlaps or meets a smooth or hard surface, you can seal the

Guide Selfbuild

Words by Mark Stephens, Paul O’Reilly, compiled by Astrid Madsen, additional information from Patrick Waterfield

Air leakage pathways graphic from the Zero Carbon Hub, zerocarbonhub.org Draughts are caused by high winds (the pressure differences between the inside and outside lead to infiltration/exfiltration) and air buoyancy (warm air rises, drawing in cooler air from outside and pushing warm air out), and may lead to interstitial condensation (warm moist indoor air that is drawn out through gaps in the envelope may hit cold surfaces in the fabric).

membrane using proprietary tape.

Remember to think about every single section of your building. It’s easy to see that your pen would lift off the paper when a floor meets a wall; this is another critical junction and the solution for maintaining airtightness depends on the type of floor construction.

For a hollow core floor it is recommended that a section of airtightness membrane be laid on top of the wall on which it is to be placed. The membrane then wraps up the side and over the top of the hollowcore flooring; the blockwork for the upper floor is then laid on top of the membrane.

This section of ‘wrapping’ membrane is then fixed to the wall or vertical membrane. In

the case of a timber floor, you have two alternatives. You can either use the hollow core floor technique or you can use tape to seal around each joist to a plastered wall.

A special tape with the same properties as the membrane will be supplied along with the membrane itself. It is very important that this tape is used correctly as even a very small gap can significantly affect the results of the air permeability test. All joints between sections of membrane and between the membrane and hard surfaces must be fully taped. Where it is necessary to cut a slit in the membrane, for pipes and cables etc, the tape must fully cover the slit and overlap the pipe/cable.

Blower door test

All new houses in ROI must be air pressure tested with a blower door test, to prove compliance with the minimum building regulation requirements. In NI, the test can be foregone in a single dwelling but an air permeability figure of 15 m3/(h.sqm) must be used in the SAP assessment, which will mean compensating measures elsewhere. The tester must have the relevant approvals from the NSAI (ROI) or the BBA (NI).

To carry out the test, a temporary frame is built into an external door with a fan that is connected to specialised software. Specific ventilators, e.g. air vents, and plumbing traps

are filled before pressurising the dwelling with a large fan.

The pressure drop across the fan will be proportional to the air leakage from the building.

Readings are taken periodically as the building pressure builds up and are continued as it decreases after the fan is turned off. In this way, the impact of different pressure effects across the building can be assessed.

The cost for a professional test on a standard house is in the order of £300/€350 plus VAT. The bigger the number the worse the result; less than five m3/(h.sqm) is doing well, while less than three is quite good for a standard house, though nowhere near the requirement for a passive house.

Bear in mind that the airtightness results will have a significant impact on the A to G rating you will get under your Energy Performance Certificate / Building Energy Rating.

Remember too that airtightness affects the efficiency of a Mechanical Ventilation with Heat Recovery (MVHR) system – higher levels of air leakage unbalance the system by either allowing warm air to escape through the fabric thus bypassing the heat recovery, or by allowing cold air to enter the building without being warmed up. Or both. So with MVHR you should be looking for a figure of two or three m3/(h.sqm), or even lower if possible.

The purpose of the test is to find the unknown leaks and to determine a value for them, not to catch the builder out. Cooperation is key to a successful outcome.

Having said that, remedial measures may be tricky, time consuming and costly and air permeability is a good indicator of build quality. Make sure your builder knows the figure you are A U T U M N 2 0 2 1 / S E L FB UI L D / 109

INSULATION AND AIRTIGHTNESS GUIDE / AIRTIGHTNESS SYSTEMS

targeting and is confident of being able to achieve it.

The test should take no more than one hour during which there will be absolutely no access to the house. Testing an occupied house tends to be more time consuming and therefore more expensive. Tell everyone who’s working on site ahead of when the test is due to take place as delays may incur an extra charge.

No wet finishes (paint, plaster etc.) should be applied within the vicinity of the test as blown dust may damage the finished surface.

All vent fans must be turned off, water taps filled and a

temporary frame/boarding fitted to an external door to allow the air tightness equipment to be positioned. All mechanical ventilation openings must be sealed prior to the test and all external doors and windows closed, (but not temporarily sealed), to provide a realistic measurement of the actual envelope leakage. Natural ventilation openings and smoke vents should be closed but not sealed.

All internal doors should be wedged open to allow rapid pressure equalisation within the building during the test.

As low wind speed is required, it may be necessary to change

the day of the test if the weather is stormy. Pressurisation tests are generally only undertaken under moderate external wind speeds of less than 6m/sec.

Wind speeds above this level can have a significant influence on the measured envelope leakage rates and test results carried out in excessively windy conditions should not generally be accepted.

A 240V mains power or a generator producing at least 15kVA for the first fan and 10kVA per fan thereafter is required, as are several 13amp mains sockets close to the working area. Alternatively extension cables can be used over a

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reasonable distance.

Repeat tests are normally 75 per cent of the original fee. If a test is cancelled after arrival on site due to non-compliance with the above requirements or others outside the control of the air testing company (apart from climatic), an additional charge, based on distance travelled, will be incurred.

A representative for the main contractor, or the client, must be on site to discuss the initial results and any implications these may have for remedial sealing.

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SIG Ireland

Why your energy efficient home needs to not only be well insulated, but also airtight.

For more information visit www.sig.ie or email enquiries@sig.ie

Insulation is an integral element of low energy construction however airtightness must also be central to an energy-efficient design strategy to reduce unnecessary heat loss. In addition, heat that escapes from the interior carries a significant amount of moisture, and this can lead to damage to the fabric of the building materials and may have a severe effect on the air quality of the living space.

Airtightness is the control of air leakage, i.e. the elimination of unwanted draughts through the external fabric of the building envelope. This may be achieved by the correct and proper installation of a vapour check or vapour barrier.

Consequently condensation, mould, rot, damp and structural damage are also eliminated.

This ensures a more viable structure, an insulation layer that can improve performance as it is now protected against penetrating moisture reducing the amount of energy-in-use in the building and CO² emissions.

It is desirable and necessary to have controlled ventilation for healthy, comfortable buildings however air leakage must be avoided.

NZEB homes are now at the forefront of the building and planning

process. Codes and standards are in place which aim to reduce carbon emissions and create homes that are healthier and more sustainable. Low carbon and zero carbon Nzeb buildings are only achieved by ensuring a high level of airtightness is attained. This means designing and installing a continuous seal around the internal fabric of the external envelope to eliminate unwanted draughts.

Once the airtight vapour layer is in place and sealed with flexible and durable tapes, it ensures that the

insulation functions to its optimum performance, saving energy and drastically reducing carbon emissions for the lifetime of the building. The airtight vapour control also ensures that condensation risk is minimised, ensuring no structural damage from moisture, mould, rot and damp.

Research shows that we can lose as much as half of all the energy used to heat our buildings through unwanted draughts, inefficient and poor ventilation. We now generally insulate new houses very well but the proportion of energy lost to draughts has increased and in some cases around half of all heat losses are due to air leakage across the building fabric. In Ireland we are not exposed to extremes in low temperatures, however our climate is exposed to high wind pressure, particularly in coastal regions.

If a vapour check has as little as a 1mm tear within a square metre area, the U value can be reduced by a factor of 4.8. This means that the calculated U value is not achieved if the structure is not airtight and hence you need a lot more energy to heat the house. Airtightness does not generally increase U values but ensures the calculated U value is achieved.

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We specialise in thermal and acoustic insulation, fire protection and moisture management products and have access to an unrivalled range ensuring your project has the right combination of products to deliver optimum building performance.

AU TU MN 2021 / SE L F B U IL D / 1 1 1

INSULATION AND AIRTIGHTNESS GUIDE / I N S TA L L A T I O N

The proof is in the pudding There is no point specifying the best system on paper if it is not put together right on site. Here are the main touchpoints to be aware of so that the insulation and airtightness system works as intended.

WATCH POINT

on issue ing is a comm Thermal loop the case insulation; in in cavity wall installed they must be of rigid boards e inside leaf. If they th tight against air gap, ere is a small th d an t no e ar hereby g can occur w thermal loopin een the insulation tw much air passes be wall, negating . al rn te in on and the ti la the insu of the effect of

1 1 2 / SE LF BUILD / AU T U MN 2021

Insulation only works if it is continuous, i.e. there are no gaps in the insulation layer.

Insulation that is not correctly installed, with gaps in-between, will never perform to its best.

Boards for instance should be held in place by stainless steel wall ties, usually covered by a plastic disc, against the outer face inside of the inner leaf, when batts or boards are being used in a partial cavity wall.

The ties should be kept clean of mortar during construction as this could cause moisture to travel from the outside in. If the insulation is blown in post construction, it should be evenly dispersed throughout the wall cavity with no gaps.

Once the insulation is in place and installed correctly, new builds will add an airtightness membrane. Airtightness is an air leakage and at times, a vapour control measure; weak points are usually found at openings, e.g. around windows.

Where such a vapour barrier or vapour check is used, this should always be to the warm side of the insulation to prevent condensation.

Examination of areas that may give rise to air leakage should be carried out continuously during the build and thus avoid any gaps or holes being covered up, or service penetrations being added without careful sealing. Pre-test devices (smaller fans which can be inserted in windows) are available to builders – these are less accurate but provide a very good indication of leakage points.

When the dwelling is completed, a further and final air tightness test must be carried out for the building regulations requirement (ROI) and in NI unless the default value was used in the design SAP assessment. In ROI you must follow Part L’s Acceptable Construction Details.

Guide Selfbuild

construction phase is to ensure all operatives on site adhere to almost military style discipline needed to locate, install and protect the airtight barrier through all phases of construction.

Sequencing the works through the various stages from foundations, floors, walls, roof, windows, doors, fixtures and finishes must prioritise sealing and protecting this airtight barrier.

Timber frame construction

Airtightness inspector

Your ‘airtightness strategy’ will need to be conducted very early on in the process and take into consideration moisture management. It is essential that all members of the construction team understand the process involved in maintaining airtightness; it’s very easy for an electrician, for example, to cut an opening in the airtightness membrane for a cable without then resealing it. It is therefore highly recommended that your builder ensures that every subcontractor on site understands the process.

And, if you are a self-builder, it is up to you to ensure that your subcontractors seal any penetrations as they go, otherwise the end result is likely to be poor and require remedial works to pass the regulatory standards currently applicable.

The challenge during the

In the case of timber frame construction, you will have to fix an airtight membrane internally on the entire envelope.

Alternatively, a certified airtight structural board may be applied internally.

It is important to ensure a dew point assessment (condensation risk analysis) is conducted to ensure the correct materials are used within the timber frame wall.

As a rule of thumb, the external layer of a timber frame wall should be at least six times less vapour resistant compared to the internal airtightness and vapour control layer, but a dew point assessment as a rule should be conducted for reassurance.

Cavity wall construction

In standard plastered blockwork, cavity walls are typically considered to be airtight as long as they are plastered externally and internally with a minimum of two coats (scratch and finish).

Potential air leakages occur where the walls are penetrated (with doors and windows for example) and adequate airtight sealing has not been considered at these junctions.

Also, it is now common practice to insulate walls internally (dryline) with insulated plasterboard (normally a 50mm board with 38mm insulation

Installation checklist Ensure detailed construction drawings are available. It is important that airtightness is considered as early as possible in the design process so that the air barrier is correctly located within the fabric. The building must be designed keeping this airtight envelope clear and visible, avoiding complex detailing. On site, constant checking of construction detailing is vital. Guidelines on how to install insulation must be followed to the letter, making sure there are no gaps and in many cases, that there is an overlap in layers.

To reduce costs and improve results, a toolbox talk should be carried out prior to any work commencing with all trades.

Coordination of works and stipulated responsibility for key junctions are critical at this early stage. The design team, site management, trades and site labourers must be made aware of the importance of airtightness and their role in achieving an airtight dwelling.

If not, it’s very easy for an electrician for example to cut an opening in the airtightness membrane for a cable without resealing it.

Test during construction. It is also important to ensure that the final blower door test is not the first, as by this stage it may be too late! There must be an intermediate airtightness quality test prior to the internal drylining or finish being applied.

In this way leaks can be more easily found and remedied.

At the end, get the as-built drawings.

This essential step is often forgotten. Instructions with full as-built drawings, detailing the materials used and clearly identifying the location of the airtight barrier, should be provided for user information.

This will help in the case of wanting to hang up a picture frame or introducing a new light pendant, allowing potential future breaches to be avoided and/or repaired if necessary.

AU TU MN 2021 / SE L F B U IL D / 1 1 3

INSULATION AND AIRTIGHTNESS GUIDE / I N S TA L L A T I O N

Shown here are gaps in the insulation; poor installation negates much of the insulating effect.

1 1 4 / S E L FB UIL D / A U TU MN 2 0 2 1

EXPERT TIPS How can I simplify my airtightness strategy?

Firstly, I would recommend moving as many services off the external walls as possible and bring them up through foundations or internal walls and use appropriate sealing solutions.

Where services do penetrate external walls, employ suitable grommets as opposed to tapes.

Airtight grommets are available in a range of dimensions.

Compared to a taped solution, grommets offer greater flexibility in that cables and pipes can be easily adjusted after the installation whereas this is not the case with tapes.

The biggest expense with airtightness is time, and any solution which may appear to cost more materially, but saves time, should be strongly considered.

Appollo Insulation

and 12.5mm plasterboard) but this may not necessarily be airtight as the junctions between the boards may not be sealed adequately: a skim coat does not provide an airtight barrier, nor does plasterboard tape!

The solution therefore is to scratch coat the blockwork walls first and then fix the insulated plasterboard. You will still need to pay particular care at window and door reveals to ensure the airtight barrier is maintained by applying an airtight seal or using proprietary tapes. The main thing to remember is that your structure is not airtight at junctions where you are only relying on the thickness of the finishing coat of plaster.

An alternative to wet plastering the inside of cavity walls which is gaining prominence is the use of certified airtight paints. Provided they are fitted correctly, these can be more efficient and cleaner to install.

An alternative method for applying an airtight barrier to a cavity blockwork construction is to apply a similar technique to a timber frame wall, that is, to

AIRTIGHTNESS

batten the un-plastered internal blockwork wall and then to apply the airtight membrane to the battens. As well as creating an airtight envelope you are also creating a cavity for any services such as electrics or plumbing, thereby eliminating any chasing, though pay close attention to the points where the services penetrate the membrane and use the proprietary tape to seal up the gaps. The final stage then is to plasterboard and skim.

DIY installation You can attend a specialist airtightness course provided

by the suppliers of the airtight membranes; if you are a selfbuilder that intends to get their hands dirty then consider attending one of the ‘contractor’ courses which will teach you every detail of applying the membranes, tapes and seals.

The same goes for insulation products; technical academies tend to be open to self-builders and will often include a review of the benefits and precepts of nearly zero energy buildings.

There are also training courses open to self-builders from Education Training boards in ROI such as the WWETB.

What are the common pitfalls when relying on plaster for airtightness?

When applied correctly, wet plaster directly on block is a reliable airtight layer, but on occasion some areas that are not exposed, can inadvertently be left unplastered.

A case in point is the area between a precast concrete slab and suspended ceiling. This area around the perimeter of a building can be substantial and if left unplastered, can lead to significant air leakage. Another classic example is an unplastered drylined chimney breast.

Airtightness will always find the weakest link, so it is critical to address all seen, and unseen areas.

Niall Crosson of Ecological Building Systems

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AU TU MN 2021 / SE L F B U IL D / 1 1 5

INSULATION AND AIRTIGHTNESS GUIDE / NEW BUILD STRATEGIES

New build energy strategies If you’re building new, you will want an energy efficient home that delivers on low energy bills and a healthy indoor environment.

Your energy strategy in a new build will at the minimum, have to meet the building regulations. As seen in the previous guide, the regulations in ROI are stricter than in NI.

Insulated foundation system

Basic regs

As seen in the definitions, the building regulations require that you build to minimum U-values, although the calculation method is in fact more sophisticated than this as it relies on energy and carbon modelling.

But there are minimums you can’t exceed, as outlined in Part L (ROI) and Technical Booklet F1 (NI). Remember, the lower the U-value the better the element is at preventing heat from escaping.

New builds in ROI must be NZEB, which is reflected in the low/good U-values you must achieve. As for airtightness, there are minimums too. The minimum as specified in the Building Regulations in ROI is 5, and anything below 3 de facto requires mechanised ventilation (see previous edition for our Systems Guide).

In NI, currently you can input a default value of 10. Best in class is the passive house standard of 0.6 ACH which is approximately less than 1cum/h.sqm.

It’s difficult to know exactly what airtightness measurement you will get at the end of the build until you do a test, but most building designers will ensure the envelope is kept airtight, most commonly with membranes.

SIPS construction

1 1 6 / SE LF BUILD / AU T U MN 2021

Walls

When it comes to choosing an insulation and airtightness strategy, there are two options.

Integrate the insulation and airtightness within the structure, or add it on later.

Modular building methods such as prefabricated concrete modules or timber equivalents known as SIPS or Structural Insulated Panel Systems, apply the insulation in the factory.

Junctions are then dealt with on site, after each of the panels have been slotted into place.

SIPS are formed like a sandwich of two boards, usually OSB (Oriented Strand Board) or plywood with a ‘filling’ of insulation, normally EPS, XPS or PUR. All the openings for windows, doors and services can be cut in the factory and the panels delivered to site with the frame of the house erected in a matter of days.

Using a similar idea, only inside out in a sense, is Insulating Concrete Formwork whereby a shuttering of expanded polystyrene is erected and concrete poured into the ‘mould’.

The double layer of polystyrene results in U-values ranging between 0.31W/ sqmK (EPS) and 0.26W/sqmK (XPS) which can be increased with the addition of insulated plasterboard on the internal

Guide Selfbuild

Compiled by Astrid Madsen with Patrick Waterfield.

leaf. As a monolithic structure, ICF is both inherently insulated and airtight once the pour is complete.

Cavity wall construction and conventional timber frame require that you layer on your insulation and airtight membranes after installation.

Therefore the first step to devising an insulation and airtightness strategy is to choose your building method, and then carry out an energy assessment to determine the optimal levels of insulation and airtightness products to install.

Another option for inherent airtightness is cob construction.

This is a method that has been around as long as humans have been creating habitats and settlements and is made from the very materials most ready to hand – earth, water, straw, lime, etc. – essentially the African mud hut or the American adobe house.

It is extremely robust, reasonably energy efficient in operation due to its thickness (thermal mass) and the thermal properties of earth. It’s an excellent regulator of moisture (when used with a lime plaster) as well as being airtight. It can also be formed into a wide variety of forms including, it should be said, entirely conventional orthogonal ones! It is also extremely fire resistant and eminently recyclable. Downsides include labour intensiveness and long construction time (including up to a year to dry out), plus it not being considered standard construction so possibly harder to insure and get signed off on by your engineer or approved by building control.

Floor

Standard floor construction consists of foundations made up of concrete and steel, with insulation and screed on top. The insulation is often PIR board but can also be the more efficient

Roofs

Rigid boards between rafters

There are two ways to insulate roofs. A warm roof insulates at the rafters, keeping the attic warm. A cold roof construction insulates at the attic floor, making the roof cold in winter.

Warm roof construction is fairly standard, even if you only use the attic for storage space, and in that case, a common roof build up will include mineral wool between the rafters and PIR or phenolic board underneath them. There are many variations and it will boil down to the U-value you are aiming to achieve. You can also include an insulation sarking layer on the outside which will remove any possibility of interstitial condensation and avoid the need to ventilate the topside of the rafters.

Airtightness membranes are usually added within the build up, which is most commonly finished off internally with plasterboard and skim.

Similar in construction is the cold roof method, with insulation between joists and often above, usually finished with chipboard or similar, depending on whether it will be used as living space or for storage. Trickier in cold roof situations is if there are any services present, such as a cold water tank or ventilation unit, which may need insulating if not already.

More expensive are preinsulated structures. ICF roofs are possible but not common for this reason, while concrete modular roofs are also possible but have restrictions on the pitch, for example. Preinsulated roof board ‘sandwiches’ are available too but don’t benefit from the overlap of the more traditional method of two layers of insulation.

phenolic board, or the more cost effective but less efficient EPS boards if you can allow for enough depth.

At the perimeter a thin strip, often 25mm, of PIR insulation board should be added added to prevent thermal bridging (most of the heat from a solid floor is lost at the edge of the slab). In addition it is common to have aerated concrete blocks which are more thermally efficient than standard blocks.

As with the wall, you could choose to integrate the insulation with the structural component.

Insulated foundations are proprietary systems, often consisting of EPS insulation, that pour the concrete into EPS moulds, similar to the ICF walls.

In the case of a storey and a half, or a two storey house, you may choose a precast concrete floor, which will be craned into place. Where the slab meets your wall will cause a thermal bridge if not insulated, as concrete is not

a natural insulator. Preinsulated slabs are now quite common to get around having to insulate this junction on site.

Other considerations

Some insulation products are more vapour permeable than others, which can be a key consideration if you are building with timber frame, for example, although non permeable alternatives can work equally well if the airtightness and vapour control strategy are well devised.

If you have a concrete block cavity wall and decide to insulate all or part of the cavity, you will often then be presented with the option of adding further insulation internally. This is commonly done by adding insulated plasterboard and makes your home better insulated, bettering your U-value.

The downside includes losing wall space (mostly an issue for renovations if the room is

already small and a lot of internal insulation needs to be added), but also losing the benefit of thermal mass, i.e. concrete and plaster’s inherent ability to store heat and slowly release it when temperatures start to drop.

In the case of a concrete or stone house, external insulation is often the most expensive way to go because of the application and the need to use specialist renders. However, in the case of timber frame, external insulation tends to be standard.

You may also consider the materials’ carbon footprint, as in how much energy it took to produce, whether it is made from recycled materials, and also whether the materials emit volatile organic compounds (VOCs) during their lifetime.

Some argue that in the case of insulation, as it is all boarded up and hidden from view, VOCs are less an issue than the choice of furnishings as many textiles emit VOCs due to fire retardants.

AU TU MN 2021 / SE L F B U IL D / 1 1 7

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Guide Selfbuild

Photo credit: Roadstone

The NZEB new build Arthur and Aoife Lambert selfbuilt their Co Meath home in 2020, beating the minimum requirements of the building regulations with panache.

With a background in construction, Arthur decided to project manage the build himself and the first step, after securing planning permission, was to work out the construction drawings.

He did this collaboratively with his insulation supplier’s technical team and his own energy consultant. The aim? Minimise thermal bridging and ensure continuity of insulation.

For the structure, Arthur and Aoife chose a concrete build as it 100 BLOCK INNER LEAF

25mm FLOOR FINISHES ON 75mm SCREED ON POLYTHENE SHEET ON INSULATION ON 150mm CONCRETE SLAB

boasts excellent thermal mass as well as fire and sound resistance.

All the stone/concrete/blocks/ hollowcore/cement/thermal screed/render and rooftiles were sourced within a 10km radius of the site, cutting down on the environmental impact of heavy haulage.

The cavity walls consist of 100mm blocks each side with a 150mm cavity in the middle. The walls are finished inside and out with a sand and cement render.

150

100 BLOCK OUTER LEAF

DPC

DPC

75

INSULATION UPSTAND

50mm BLINDING 200mm COMPACTED PERMEABLE LAYER 100mm CRUSHED ROCK. TAKEN DOWN TO SUITABLE GROUND

DAMP PROOF COURSE

950mm (600mm Min)

50

RADON MEMBRANE

150

RADON MEMBRANE

The upper storey floor consists of precast concrete hollowcore slabs which were craned into place.

Floors

“I initially considered an EPS passive foundation system but, with the help of the energy assessor and the technical team at the insulation company, we delved a bit more into actual thermal performances.”

“That’s the main reason we chose a traditional strip foundation system with a medium density (thermal) block, and PIR riser panels,” says Arthur.

Using a thinner material than EPS was also important to reduce construction waste.

“The vast majority of concrete materials are now recycled, but dig out materials end up dumped,” he adds.

The floor insulation was a hot topic of debate. “We first considered using two layers of the typical 2.4m x 1.4m board insulation – staggering the joints and using two different thicknesses, and using a tape to seal it all off, making sure all the areas were filled.”

Instead, his technical advisors suggested a 150mm PIR tongue and groove insulation board

OVERVIEW Bedrooms: 5 House size: 3,500sqft Airtightness: 1.14m3/h.sqm Thermal bridging (Y-value): 0.021 Heating and hot water: 16kW air to water heat pump, with underfloor heating throughout on 15 zones Ventilation: mechanical with heat recovery BER: A2

installed over the 150mm concrete floor slab, which delivered a U-value of 0.12W/sqmK. “We have large open square areas and the installation was quick (we got it done in a day), and straightforward with the boards all clicking into each other. It was a tight fit, there was no taping required, and there was very little cutting.”

Because hot air rises, the hollowcore upper floor was insulated with 50mm of PIR insulation. This created a buffer between the upper and lower storey heating zones.

A U T U M N 2 0 2 1 / S E L FB UI L D / 119

INSULATION AND AIRTIGHTNESS GUIDE / NEW BUILD PROJECT ROI

Play Room Roadstone

Bathroom

Utility

Dining

Kitchen Island Unit

Living

Sunroom

Hall Family Room

Walls

The cavity was insulated with 150mm full fill PIR boards, including pre-formed corner PIR boards to ensure continuity of insulation at the corners, achieving a U-value of 0.13 W/sqmK. But with cavity wall insulation, installation can be tricky. “The

“There were cross sectional videos of where everything went, the important little DPC strips, and the corners.” With the videos fresh in the block layers’ minds, the energy consultant along with the insulation suppliers followed up by arranging toolbox talks on site.

This meant the block laying team was aware of the importance of good detailing, and carefully recorded that the thermal envelope was built in accordance with the Department of Housing’s Acceptable Construction Details (ACDs).

To minimise thermal bridging, thermal blocks were also used in the walls. Specifically, above

SUPPLIERS Insulation design service and products Xtratherm, xtratherm.ie Thermal blocks, screed, roof covering Roadstone, roadstone.ie Systems Maynooth Plumbing and Heating, maynoothplumbingandheating.ie

insulated cavity closer to ensure continuing of insulation between wall and roof,” adds Arthur.

Other than tapes and membranes at junctions and windows, the main airtight layer in the walls is a 25mm sand and cement render on the inner face

block layers watched all the installation videos that the insulation suppliers provided, which were absolutely invaluable because they broke down the process,” says Arthur.

50x25mm C16 TREATED TILING BATTENS EAVES VENTILATOR OVER INSULATION ROOFING FELT

INSULATION BETWEEN JOIST AND OVER WALL PLATE FASCIA, SOFFIT AND GUTTERS

50mm DEEP BIRDSMOUTH IN RAFTER 100x75mm C16 TREATED TIMBER WALL PLATE ON CONTINUOUS MORTAR BED

BLOCK OUTER LEAF

30x5mm GALVANISED HOLDING DOWN STRAP AT 1.2m CTRS.

BLOCK INNER LEAF CAVITY INSULATION

1 2 0 / S E L FB UIL D / A U TU MN 2 0 2 1

and below the hollow core first floor, at the eaves, underneath the window board and sitting on top of the concrete lintels.

The window jambs fit snugly on thermal L blocks as well.

“We then used an L-shaped

of the walls, with paint-on airtight membrane used at wall chases.

The ends of the hollowcore floor, wrapped in membrane, sat in a bed of mortar and taped to blockwork.

Guide Selfbuild

Bedroom

Roof

The pitched roof, for its part, was insulated with 150mm PIR board insulation between the rafters, allowing a 50mm gap above for the windtight membrane and roof tiles. A 75mm PIR board follows below, directly screwed onto the rafters. The combination results in a U-value of 0.11 W/sqmK. Then came the awkward bit: how to detail the seven dormers.

These are a direct result of the planning officers wanting a storey and a half design.

“We boxed the dormers in, made them a bit smaller to get a robust detail and to get more

insulation over and around the window units,” says Arthur, as dormers are notoriously tricky to detail for airtightness and continuity of insulation.

“Anywhere there was any sort of a cavity, it was filled with the pitch roof insulation.

The dormers and pitched roof ceiling were then sealed with airtightness tapes and membranes. A lot of time and care was taken as it really was intricate detailed work.”

The verdict: the house is warm and comfortable with minimal heating bills.

Bedroom

Bathroom Bedroom Hotpress

Dressing Room

Ensuite

Ensuite Bedroom

Bedroom

Project Supplier

087 202 3816 info@maynoothplumbingandheating.ie

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We have a skilled team offering an extensive range of plumbing and heating services specialising in complete new build installations using the market leading Samsung Air to Water Heat Pump supplied by Joule.

All information is available at www.maynoothplumbingandheating.ie A U T U M N 2 0 2 1 / S E L FB UI L D / 121

INSULATION AND AIRTIGHTNESS GUIDE / NEW BUILD PROJECT NI

As warm as toast Our choice of insulation products, and our airtightness strategy, were based on our build method and our desire to pre-empt any mishaps on site, writes self-builder Brian Corry who’s on a mission to build himself an eco house in Co Down.

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In my article in the Spring edition, I explained why we had chosen a single skin glulam timber structure as our build method. One reason was because it allowed moisture to escape.

So when it came to choosing how to insulate the structure, there would have been little point choosing an insulation product that would lead to interstitial condensation between the wood structure and the insulation.

I am sure you know what would happen if you tried to make toast in a microwave – you’d end up with a soggy lump of bread because the steam cannot escape!

Insulation

The single skin glulam walls are 100mm thick so the insulation needs to be fixed externally as a board, although it is possible to insulate internally too. This limited our options somewhat, as it ruled out all cavity fill products.

The obvious choice was wood fibre insulation. Not only is it a pretty good insulator, it is also carbon neutral and some manufacturers even claim carbon negative. So it is in good company with the glulam walls.

To meet our target wall U-value of 0.16 W/sqmK we needed 200mm of wood fibre insulation fixed externally in addition to the insulation provided naturally by the glulam walls themselves. Similarly, the roof will be insulated to achieve 0.14 W/sqmK with wood fibre, which means that the house should be as warm as toast.

For the floor we took a different tack because our primary concern here was to ensure that there would be no cold bridging, as well as achieving a U-value of 0.15 W/sqmK. Vapour permeability was not a consideration, so we had a lot more options available to us.

In the end we made the decision to go for a precast insulated (EPS) concrete flooring system for ease of installation with the minimum chance of errors that could lead to unintended thermal bridges or gaps, and confidence that it will meet our thermal target.

Airtightness

Despite specifying the correct amount of insulation, it could be largely wasted if we did not ensure that the house was airtight and free from draughts.

The HBE glulam we chose

Guide Selfbuild

is a tongue and groove system and naturally offers significant airtightness in itself however we still need an airtight, yet vapour permeable membrane, to envelop the walls and roof. We will do this by sandwiching an airtight membrane between the insulation and the external face of the HBE glulam walls.

The insulation effectively pins the membrane to the wall and similarly on the roof. Our cladding then attaches to timber battens that are themselves screwed back to the glulam wall with a further membrane to protect the external face of the insulation should any water get past the cladding.

Whilst every effort has been made to maximise the vapour permeability of the structure, it still requires Mechanical Heat Recovery Ventilation to ensure

that the air is kept fresh, and the moisture generated from bathrooms and the kitchen is removed efficiently.

Site proof

Having a plan is one thing, making sure it survives contact with joiners, electricians and all the other trades is another.

The placement of the membrane between the external wall of the structure and the insulation will mean that it will be pretty much inaccessible to most trades. Indeed, they would need to drill a long way to hit it!

In addition, we have dedicated ducts to bring in all the cables and pipes so there is no need for anyone to drill a hole through any part of the structure.

The trades will be pretty much able to nail, screw and drill to their

“Whilst every effort has been made to maximise the vapour permeability of the structure, it still requires Mechanical Heat Recovery Ventilation...” heart’s content inside without fear of accidentally piercing the membrane. Having said that, I still intend to brief everyone thoroughly so that they are aware of the situation.

Read up on Brian’s journey so far in his Building the Dream series on selfbuild.ie

Corner wall section (View from the top) Horizontal treated batten to suit timber cladding Vertical Timber Cladding fixed with stainless fixings to horizontal treated batten Nailband behind batten for airtightness Huettemann HBE structural timber

12.5 Plasterboard - skimed or jointed

140mm Pavatherm Insulation - Shiplapped and fixed with STR-H fixings

Pavatex DSB2 Membrane fixed and taped

60mm Pavatherm Plus T&G connection - fixed with thermowasher fixings

140mm Treated Timber battens for fixing insulation with Thermowasher fixing

Pavatex ADB Membrane

Thermowasher and Fixing - minimum 40mm lumber penetration.

Render Board 12mm with minimum ventilation gap of 38mm fixed to battens over insulation. Shown with 45mm Treated Thin Coat Through Colour Render system Timber batten to provide fixing for render board

AU TU MN 2021 / SE L F B U IL D / 1 2 3

INSULATION AND AIRTIGHTNESS GUIDE / RETROFIT STRATEGIES

Energy upgrades The single best way to make your home consume less energy is to insulate it and make it airtight, before you even consider upgrading your heating system or replacing the windows.

As seen at the start, the first step will be to evaluate what state your home is in.

To determine what level of insulation and airtightness it already has, and what would be the best way to go about upgrading it, you will need an energy assessment done.

In many cases, for an existing house, the assessment will make assumptions depending on the year the house was built and what type of construction it is. Your house may in fact be more energy efficient (old stone houses apparently perform better than previously thought) or indeed less energy efficient in practice than what the report says on paper (which might be the case if the insulation wasn’t installed very well at the time of building).

Despite this limitation, your energy upgrade will very much depend on the results of the energy assessment report as that is the only data available to you. The report will be based on a site survey, and can be carried out through your insulation supplier or an independent energy assessor that you hire directly yourself.

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To avoid interstitial condensation, your construction drawings need to be put together so that the insulation and airtightness strategy will avoid any moisture build up.

Your energy assessor or your insulation supplier will do this condensation risk analysis for you.

It’s best practice to hire your own independent advisor, to avoid conflicts of interest but also so you can have a second opinion if there are any questions that arise in the design or on site.

As with a new build, if one area of the house is weaker than another in terms of energy efficiency, e.g. because there are a lot of windows or they have a poor performance, you can compensate for it by increasing the insulation in the walls next to it. In the case of windows, draughtproofing can help (see below).

Again, as highlighted earlier, a crucial aspect to bear in mind if you plan to upgrade the energy efficiency of your home is how you will ventilate it. Natural ventilation may no longer be adequate.

Deep vs. shallow retrofit

A shallow retrofit is a small upgrade, such as, say, adding insulation to the attic space. As warm air rises, it is the lowest hanging fruit and the most cost effective measure. But to get down to really good energy efficiency levels you need to look at the house as a whole and consider how every element contributes to your goal of low energy bills or works against it.

Therefore a deep retrofit will upgrade the entire building fabric, based on a thorough energy assessment of the house, and will include not just an insulation upgrade but also an airtightness upgrade, window replacement, and a new centralised ventilation system. This can include a new heating system too. Deep retrofits require invasive work,

which people often use as an opportunity to re-plumb and re-wire the property at the same time.

Fabric upgrades

Floors can be especially disruptive to upgrade so are only usually done when there’s a complete renovation, oftentimes to accommodate underfloor heating pipes. But even with a deep retrofit, floors may not necessarily be insulated.

However in that case, other parts of the house will need to compensate for the floor’s relatively poor performance.

Where an insulation upgrade is necessary in the floor, there is digging to do, with digger access issues to consider, hardcore, blinding and radon barrier as you would a new build, then the insulation boards. The depth

Guide Selfbuild

Compiled by Astrid Madsen with Patrick Waterfield.

reduction in internal volume.

As the method of applying plasterboard and painting directly over it is known as drylining, some refer to this method of insulating internal walls as drylining too. This method requires a robust condensation risk analysis and depending on the situation, you may need to add a cavity between the internal wall and the stud wall you will insulate, further decreasing room size.

Grants

€£ € £

Grants for energy upgrades in NI are modest when sought through utilities, but there are some attractive grants available to low income earners though the Affordable Warmth scheme for which you can apply through your local authority. These are focused on shallow retrofits.

In ROI there are attractive grants that can fund almost all of the cost of an insulation upgrade – this is only open to those on social benefit, including pensioners. Everyone else who owns a house that was built before 2006 can avail of more modest cash grants.

Apart from these shallow retrofits, the SEAI’s One Stop Shop (OSS) scheme is targeted at deep retrofits and will usually fund around of 35 per cent of the cost of the works, including windows and doors.

As the homeowner, you will apply for the shallow retrofit grants yourself. In the case of deep retrofits (ROI) you will need to go through an approved OSS.

Top 3 tips for a successful home energy upgrade Keep an open mind about what the best type of installation might be for your home. Even if you have a set idea of what kind of insulation upgrade you want, the best solution will be determined by the house itself and the energy assessor’s report. For example, if your house has solid walls, external insulation might be a good option: EPS for concrete, rockwool for stone walls. If your house has cavity walls, pumping them with EPS bead is usually very effective but only if the cavity is more than 40mm wide and the house isn’t in an exposed area. There are many other factors to consider, so these guidelines may not always apply.

1

Look for credentials.

Make sure the insulation contractor you are going to hire is reputable, i.e. do a background check on the company by speaking with previous clients and checking how long they have been in business for.

2

Check the Agrément cert. External wall and cavity wall insulation systems are certified by Agrément certificates. Ask your insulation contractor what system they will be installing and check the NSAI (ROI) / BBA (NI) website for the cert. This will detail how the insulation system is to be installed to the proper standards.

3

Roadstone

you can go to will depend on the depth of the house foundations – this can be readily checked if there are suspended floors, or may require an inspection from the outside by digging down.

Another option is to add insulation onto the existing floor, but this will have considerable knock-on effects on things like ceiling height, door opening heights, socket placements, etc.

For the roof, while insulation rolls above the ceiling are often the most straightforward and cost effective solution, it may not be possible to do so if the floor is sloping or hard to access.

In that case insulating from the underside of the ceiling, in the room below, may be the best option. Insulating at rafter level is also possible but a more complex job, and usually involves introducing insulation between the rafters and underneath. Spray foam and cellulose insulation are among the alternatives.

When it comes to the walls,

you can insulate any which way: on the outside (external wall insulation or EWI), inside the cavity if you have one, or indoors.

EWI is a specialist product so you will need to buy a system from a reputable manufacturer and make sure the installer is trained in installing that product.

There are two types of EWI: EPS or rockwool sheets which are mushroom fixed onto the wall, and a proprietary coat of plaster is applied on top.

There are restrictions using EWI, for instance your windows and soffits need to be able to accommodate the extra depth, and rainwater goods will need to be repositioned. Window sills may also need to be extended, e.g. with a new uPVC one overlaying the existing concrete/ stone – if this solution is not acceptable then sills may need to be replaced.

In an existing home, the most common way to insulate a cavity, even if it has insulation in it already, is to pump EPS beads, along with a binder, into it through a series of holes. Blown fibre can be sucked out before new material is blown in. Again, check what make is being used and that your installer is trained in its installation. Some exposed locations aren’t suitable. Spray foam insulation is an alternative, albeit generally more expensive, and is installed in the same way – same checks apply.

Often the least expensive, and most open to DIY, is to insulate on the internal wall, usually with insulated plasterboard (usually a PIR board glued onto a sheet of plasterboard) although most insulation types can accommodate this method.

Disadvantages include disruption inside the house while works are going on, issues in relation to detailing around openings and any existing plasterwork features (cornicing, etc.) as well a slight

Minimum regs In both NI and ROI energy upgrades are subject to the building regulations.

Chris Garry Breffni Insulation, breffniinsulation.com

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INSULATION AND AIRTIGHTNESS GUIDE / RETROFIT STRATEGIES

In NI, when renovating existing thermal elements, where more than 50 per cent of the surface area of an individual thermal element or more than 25 per cent of the total building envelope is being renovated, where the U-value of existing thermal elements (walls, roof, etc.) or fittings (e.g. windows) is worse than a certain threshold level the whole of that element should be upgraded to improved U-values as stated in Technical Booklet F1 (subject to economic feasibility defined as simple payback period of 15 years).

Extensions can be addressed using either the “Standards Based Approach”, whereby

minimum standards are met as above, or the “Equivalent Carbon Target Approach”, where SAP is used to demonstrate that the overall performance of the dwelling with the proposed works is no worse than it would have been under the standards based approach. This approach can be used, for example, where an extension is proposed and the Standards Based Approach cannot be achieved. In that case measures can be carried out to other parts of the building to compensate.

Where the work involves replacement of controlled services (e.g. heating system components) minimum

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performance levels must be achieved. Refer to the UK “Domestic Building Services Compliance Guide” for more details.

Particular requirements apply for a change of use (e.g. dwelling being created in previous commercial/industrial/ agricultural premises) and change of energy status (e.g. previously un-conditioned space becoming conditioned). Refer to Technical Booklet F1 for details.

In ROI there is a requirement for “Major Renovations” to meet a “cost optimal” energy performance standard (a minimum BER of B2) insofar as this is “technically, functionally and economically feasible”.

“Major renovation” means the renovation of an existing dwelling where more than 25 per cent of the surface area of the existing building’s thermal envelope undergoes renovation.

Thermal envelope meaning the entire surface area of a building through which it can lose heat to the external environment or the ground, including all heat loss areas of walls, windows, floors and roof.

As an example, if you install external wall insulation combined with say upgrading existing windows and doors, then this could very easily add up to 25 per cent of the surface area of the thermal envelope.

Unlike the planning requirement, that states that anything more than 40sqm needs to apply for planning permission, the 25 per cent rule is not intended to be aggregated over time.

In all cases you must get your energy assessor, architect or other suitably qualified building professional to determine whether you fall above or below this threshold.

If your project does upgrade

more than 25 per cent of the building thermal envelope then the entire upgraded dwelling must either achieve a B2 Building Energy Rating or implement a package of pre-defined energy performance improvements set out in Part L’s Table 7.

Table 7 shows that achieving compliance in existing dwellings typically may involve adding a minimum 100mm of external wall insulation, 300mm of attic insulation and upgrading old boilers to 91 per cent efficiency gas boiler with full time, temperature and zone controls.

Improving airtightness

If you plan to carry out a deep retrofit, an airtightness and ventilation strategy will be included. But if you are not looking at a big job and want to reduce draughts yourself, then it’s a question of reducing unintentional air paths as far as is practicable.

Where possible, fit draughtstripping in the frames of openable elements of windows, doors and roof lights. Ensure boxing for concealed services is sealed at floor and ceiling levels and seal piped services where they penetrate or project into hollow constructions or voids.

The addition of a draught lobby may be advised in some instances. Address air leakages into the attic from the attic side, considering pipes and cables.

Also seal around loft hatches.

Remember that the more you seal off your house, the more you need fresh air circulation, i.e. need to make sure the indoor air quality remains high. This means looking at whether your current ventilation system is still adequate after the upgrade.

www.midlandheating.ie Tel: 046-9430529 Email: sales@midlandheating.ie

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INSULATION AND AIRTIGHTNESS GUIDE / NZEB ENERGY UPGRADE Photography: Denis Vahey Words: Astrid Madsen

Operation renovation This 1940s Co Waterford cottage was upgraded to become a super energy efficient home in 2019. The renovation was such a success it won the Sustainable Tipperary NZEB Design Competition. Here’s how they went from a G to an A3 eneryg rating.

WC

BEFORE 45sqm

Kitchen

BEFORE

Bedroom Bedroom

Bedroom

Living

Dining rl over

Kitchen

AFTER 153sqm Living

Utility a/w heat

pump

hrv

Bedroom

HALL

Wardrobe Bedroom

Bedroom WC

Bathroom

Most people don’t decide to heavily invest in upgrading the energy efficiency of their home unless they have bigger plans, such as, say, adding an extension.

Their motivation also tends to be quite clear. They may have just bought a house, wanting to make it comfortable for their family. Or they may want their existing home to be more comfortable and maintenance free.

James and Phil Hallinan are a case in point. Nearing retirement, the couple inherited an old cottage which they decided to do up by increasing the floor area. To make the house warm, healthy and efficient to run, they also invested in an energy upgrade.

The extension

The house was an L shaped 1 2 8 / SE LF BUILD / AU T U MN 2021

cottage containing three compact bedrooms, a living area and previously added extensions with small kitchen and bathroom.

The concept of the redesign was to orientate the living spaces around a south to west facing patio, which would also act as a new entrance to the home.

Budget constraints, and not wanting the extension to be visually obtrusive meant the

THE BRIEF ü Bigger living area that retains the views ü Seamless connection between extension and existing cottage ü Retain the total of three bedrooms, but with a new master bedroom with ensuite and walk-in wardrobe ü New kitchen and new main bathroom ü New utility room with plenty of storage

Guide Selfbuild

Insulation strategy

couple agreed to incorporate the circulation spaces, where possible, within the main living areas. Therefore the size, and costs, of the extension were kept to a minimum.

There was no insulation at all in the existing cottage.

For the walls, the most efficient and cost effective solution was to insulate internally with a proprietary insulation system which included 100mm rockwool. The existing timber floors were removed, with a new concrete slab and fully insulated (150mm PIR board) floor screed on top.

The roof was stripped back to the existing rafters, luckily providing good ceiling heights, and a new warm roof (insulated with 70mm PIR and 150mm mineral wool, and made airtight, at rafter level) was installed.

“Mineral wool is typically the only thing we use between rafters,” says Alan the architect.

“We would always use warm roof construction so having a good quality product that you know won’t shrink is important.”

“My preference would always be external insulation if the

budget and design suits,” adds Alan. “We did actually externally insulate the old porch with PIR and used a vented rainscreen detail over.”

The extension, for its part, was built to passive standards with thermal breaks and cold bridges detailed out.

For the extension floor, a standard build up was the most cost effective consisting of 150mm PIR insulation with screed over, and thermal blocks to the perimeter.

Then a 200mm full fill cavity with EPS beads turned out to be the most cost effective to achieve a good quality insulated wall, with 30mm insulated plasterboard internally to negate the issue with wall ties causing thermal bridging.

When using some rigid boards in the cavity wall, installation is critical to get the U-value you are aiming for. “Unless they are specifically trained, block layers should not be installing insulation,” opines Alan.

“The other advantage of the

bead is that there is no waste and it helps with airtightness; we would usually expect an airtightness result of 1 to 1.5m3/h.sqm at 50Pa on a new build. Anything under 2.5 is usually respectable on an existing extension refurb.”

Airtightness strategy

Preliminary air tests showed results of approximately 2.4 m3/hr/m2 for the whole house, achieved by careful and thoughtful design, and meticulous construction procedures.

The existing fireplaces and chimney stacks have also been removed, drastically reducing the opportunities for air leakage by infiltration.

Junctions and details were kept as simple as possible, to provide clarity for the contractors, and to reduce the possibilities of unintended air leakages.

Before and during the construction process, all trades involved were made aware of the intent to make the house as airtight as possible.

Regular on site meetings with the contractors allowed for continuous monitoring of the construction standard.

This ensured that mistakes could be avoided, and that the contractors could be advised as to how to properly construct details and junctions. By doing this, the airtightness could be

AU TU MN 2021 / SE L F B U IL D / 1 2 9

INSULATION AND AIRTIGHTNESS GUIDE / NZEB ENERGY UPGRADE

Roadstone

maximised as much as possible, and construction processes that would have led to air leakage were avoided.

Systems

Builder Gerry and Sean of Byrne and Byrne Construction, byrneandbyrneconstruction.ie

For ventilation, the house relied on the opening of windows and doors for air changes. As the energy upgrade made the home airtight, a new heat recovery ventilation system was installed to provide ample fresh air and keep the indoor environment comfortable for the occupants, without the need for opening doors and windows.

1 3 0 / S E L FB UIL D / A U TU MN 2 0 2 1

provided by a wood burning stove, with dedicated supply air, located in the new living room.

Sustainable Energy Authority of Ireland grant for insulation upgrades, but for some reason the grant would not cover the warm roof detail – they wanted us to insulate at ceiling level/on the roof space floor.”

“For the walls, older buildings have difficulty availing of the scheme because solid stone walls do not compute in calculating the BER,” he adds.

Phil and James are however in the process of applying for their heat pump grant, which they are thankfully eligible for.

“The advice we would give to others thinking of going down a similar route is to check what

grants are available before starting the project,” says Phil.

“Ensure you go over every detail with the contractor before works begin. And have everything completed before moving in, this includes the landscaping, lawns, fencing and entrance gates.”

Grants

Despite the amount of insulation that went into this renovationcum-extension project, there was no grant available for the insulation upgrade.

“I did speak to Superhomes, which is a one stop shop energy upgrade centre run by the non profit Tipperary Energy Agency,” says Alan. “But as the grant would only cover works to the existing house, and because the extension was larger than the house, it would not qualify.”

“We then looked at the basic

Roadstone

All the main living spaces have ceiling heights in excess of three metres, which allows for greater air movement and greater control of the internal environment. A rooflight purges hot air on very warm days.

Shading is provided to the South West facade, to control solar gain.

For heating, the existing 1920s house had an oil boiler with radiators throughout the house. Secondary heating was provided by two fireplaces, which as outlined above were removed.

These were replaced with an air to water heat pump, as well as underfloor heating throughout.

Further heating is now also

Top 3 tips for a successful Architect home energy Ed and Alan Walsh of Walsh+Walsh, wwarchitects.ie upgrade SUPPLIERS