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the high-performance housing magazine

sUMMER 2015

residential winner

2015 canadian green building awards

Beechwood deep energy retrofit

Urban Straw Bale Reno Renewed Tudor-style home gets energy cut

RIGID FOAM PANELS Not all the same

THE ECOHOME DEMO HOUSE

Stage three: efficiency with heat pumps ecohouse CANADA | SUMMER | 2015

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The national source of information on Canadian sustainable high-performance homebuilding in partnership with www.ecohome.net.

sUMMER 2015 6

THE ECOHOME DEMO HOUSE STAGE three Increased efficiency with heat pumps

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house in low

Study shows there is more to thermal performance

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AWARDS

residential winner 2015: Beechwood deep energy retrofit

23 urban straw bale reno

PR O J E C T G BUILDING N

Beyond R-Values

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T IA L W E N N G I NN D RE I DIA E A

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Off grid, passively-heated home achieves LEED Gold

Renewed 90-year old Tudor-style home gets big energy cut

27 Energy evaluations

How they can guide a renovation

29 RIGID FOAM PANELS NOT ALL THE SAME Where they are best used

SEE MORE at • www.sabmagazine.com u click on ecoHouse Canada • www.ECOHOME.NET Cover: Beechwood house. Photo: Greening Homes Ltd.

ecohouse CANADA | SUMMER | 2015

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DELTA® protects property. Saves energy. Creates comfort.

Creative Building Design Requires High-Performance Membrane Solutions. The Denver Botanic Gardens Science Pyramid presented a unique air and moisture challenge. The pyramid shape, usage, and open cladding multiply the complexity of maintaining a watertight exterior while managing the moisture generated within. Two air and moisture barriers, DELTA®-VENT SA and DELTA®-FASSADE S ensure an airtight and watertight enclosure that manages moisture in a complex Colorado climate. The UV-resistant, matte black DELTA®-FASSADE S adds depth and dimensionality to the open cladding, heightening the striking appearance of this landmark building. When architects want to push the boundaries of building design, one of the biggest complications is moisture control. High-performance solutions like DELTA® products will allow architects full artistic freedom while giving them the confidence of a leak-free building. If you are designing a unique structure, don’t hesitate to contact DELTA® to protect you from future moisture issues.

DELTA®-VENT SA

Vapor permeable self-adhered water-resistive barrier & air barrier.

DELTA®-FASSADE S

UV-resistant water-resistive barrier for open joint claddings.

1-888-4DELTA4 (433-5824) - www.cosella-dorken.com 4

ecohouse CANADA | SUMMER | 2015


A sister publication of:

message from the publisher

publishing partners:

RESIDENTIAL WINNER SHOWS weRe we cAN go

canada green building council

Photo: Roy Grogan

VISIT www.sabmagazine.com for our Product Directory

publisher Don griffith 800-520-6281, ext. 304, dgriffith@sabmagazine.com marketing manager Denis Manseau 800-520-6281, ext. 303; dmanseau@sabmagazine.com graphic Design carine De Pauw 819-778-5040, ext. 308, cdepauw@sabmagazine.com senior account manager Patricia Abbas 416-438-7609, pabbas8@gmail.com eDitorial aDVisors • Tom knezic, M.ARCH., LEED AP, OAA Solares Architecture Inc., www.solares.ca • Roy Nandram, LEED AP, RND Construction, www.rndconstruction.ca • Mike Reynolds, LEED AP-Homes, ecohome.net published by:

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The winning projects Eight high-performance, sustainably-designed buildings [seven commercial/institutional and one residential], all awarded in the 2015 Canadian Green Building Awards, point to a future in which the buildings where we live and work will be far superior to what we know today.

Launched in 2008, and offered annually by the Canada Green Building Council [CaGBC] and Sustainable Architecture & Building [SABMag] and ecoHouse Canada, the Awards recognize excellence in sustainable, high-performance building design in order to advance knowledge and improve practice for the design of nonresidential and residential buildings. This is amply demonstrated in the winning residential project, the Beechwood Deep Energy Retrofit by Greening Homes Ltd. in Toronto featured in this issue, a post-World War II bungalow transformed into a highly-efficient two-storey home: a retrofit that exceeds Passive House air-tightness requirements for new construction. The central message of the Beechwood project is that we have the knowledge and products to make our houses much more energy efficient and with healthier indoor air quality than the houses which we are building, and for about the same cost, especially if building new. Publicising high-performance housing is the purpose of ecoHouse Canada, which is why we became involved in the Demo House Video Building Guide, a 20-part series on the techniques and products for building high-performance housing in the Canadian climate. The first five videos can be seen here: http://www.ecohome.net/video/guide. The annual Green Building Awards gives us a look at a promising future. We thank our sponsors Interface, the Canadian Precast Prestressed Concrete Institute and Uponor without whom the 2015 Canadian Green Building Awards would not have been possible.

ISSN 1920-6259 Copyright by Janam Publications Inc. All rights reserved. Contents may not be reprinted or reproduced without written permission. Views expressed are those of the authors exclusively.

- Don Griffith, Publisher

Publication Mail Agreement #40024961 Return undelivered Canadian address mail to: Janam Publications Inc., 81 Leduc St., Gatineau, Qc J8X 3A7 The print version of ecoHouse Canada uses a 100% post-consumer fiber that is certified FSC and EcoLogo. It is processed chlorine-free, FSC-recycled and is manufactured using biogas energy.

Please forward comments, article ideas and project contributions to: Don Griffith, Publisher dgriffith@sabmagazine.com - 1 800 520 6281 ext.304

Environmental savings for this issue:

Fsc logo

14 Trees

52,769 litres water

799 kg waste

2,078 kg CO2 ecohouse cANADA | SUMMER | 2015

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Td he em eo ch o ho ou ms ee update

STAGE Three Increased efficiency with heat pumps working in tandem

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Our previous update covered aspects of the building envelope which allowed us to reduce the annual heating requirement to about the Passive House standard of 15 kWh per square metre. Windows are a part of that but they are also part of our energy performance strategy. The house is laid out south facing to maximize passive solar heat gain, so we have designed and chosen windows to take best advantage of that. By Mike Reynolds

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Window glazings on the north, east and west have an R value of 8.4, but intentionally only R 6.4 on the south, due to different Low E coatings. Low E coatings reduce heat loss, but they also reduce heat gain. By sacrificing that 30% of the insulation value on the south side, we were able to increase the amount of passive heat gain we would have by 80%. In houses that perform at this level of efficiency, domestic hot water becomes the single biggest consumer of energy. To tackle that, we have two heat pumps which together will reduce that energy demand dramatically. A Mitsubishi ‘Mr. Slim’ split heat pump will provide heat to the house; we also have a heat pump water heater from AO Smith. The Mr. Slim operates efficiently down to -25 °C at close to a 3 to 1 ratio of consumption, meaning three units of heat out per unit of energy in. That is three times more efficient than a standard electric baseboard heater which offers you only a 1 to 1 ratio. The AO Smith water heater is an air-to-water heat pump which extracts heat from the air to generate hot water, so in the winter that 3 to 1 heating ratio of the first heat pump is transferred to the water heater. And the more ‘free’ heat you have in winter [solar gains and general occupancy] the more efficient it becomes. In the summer it acts as an air conditioner as it extracts heat from the air to generate hot water, in a way giving you ‘free’ hot water, since rather than ejecting heat from your home as most air conditioners do it is retained in the form of domestic hot water.

Since two-thirds of the bulk energy consumption in a home is usually a result of heating, with our building envelope we’ve been able to reduce that to about 10 percent of what most new homes require. Beyond that, the next big leap in efficiency comes from reducing interior loads. Heat pumps are a great way to do that, particularly with hot water. Our heat pump combination together is surprisingly affordable, and it has taken a big chunk out of the total energy required for the operation of the house. To get a better look at what we’ve got going on so far and some of the fancy features still to come, check out the Ecohome Building Guide at ecohome.net where you can see the first five videos in the series. When complete the Ecohome Building Guide will document the entire construction of the house. We thank our product sponsors: Roxul, W.R. Meadopws, Kott Lumber, Uponor, Ecogenia/Lunos, CGC, Fantech, Delta [Cosella Dorken], Mitsubishi Electric Canada, American Standard, Benjamin Moore, A.O. Smith, Riopel , Columbia Forest Products, Les Fenêtres Élite Inc., Cosentino Canada, Glendyne, Isocork Canada, Rainfresher, Bostik and Aeratron.

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The south-facing windows have a lower Low-E coating to allow for more passive heat gain in the winter [1]. The components of the Mitsubishi ‘Mr. Slim’ split heat pump which will provide heat to the house with three times the efficiency of baseboard electric heaters [2]. The AO Smith water heater is an air-to-water heat pump which extracts free heat from the air to generate hot water [3].

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news

Housing development aims for 28% energy savings In its new development of 185 homes in the Region of York near Toronto, Mozaik Homes is participating in a pilot project which is anticipated to achieve 28% energy savings based on the model that was created in collaboration with the Savings by Design program. A conservation program offered by Enbridge Gas Distribution to residential and commercial builders, Savings by Design assists in obtaining higher levels of performance through the application of the Integrated Design Process [IDP]. Facilitated by Sustainable Buildings Canada, builders and developers participate in an IDP workshop to understand how to improve energy and environmental performance. Info: www.savingsbydesign.ca.

BOOKS Sustainable Residential Architecture by Ana Maria Alvarez Reviewed by Jeffrey Thorsteinson Head Writer & Researcher, Winnipeg Architecture Foundation and Republic Architecture Inc.

As a term, if not in practice, sustainability is everywhere. Tossed around liberally, the word is an all-but necessary ingredient in building proposals, political statements and the like. The ambitions embodied in this practice are good. But omnipresence can create meaninglessness, a dire truth given that so much

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remains unsustainable. To be more than a platitude sustainability must go beyond the superficial, must even disrupt. Enter Ana M. Alvarez’s Sustainable Residential Architecture. Heavy and gleaming, the book appears to be exactly what’s needed: an in-depth exploration of sustainable architecture that gives the real thing mass appeal. But while a picture is worth a thousand words, sometimes you need a paragraph. On that count this book falls short. From its scant introduction to barelythere project descriptions, Alvarez’s text is so thin as to leave us guessing as to what makes these buildings sustainable. Without much on which to base a reading, what stands out is what’s missing, including heritage re-use and multi-family residences. Some lovely works are included, notably Wolfgang Feyferlik’s Stockner House and FLOAT Architecture’s Oregon Watershed – a positively Thoureauvian retreat. But as a view of sustainable architecture, the book is limited, featuring single-family homes and cottages less alluring but comparable to an average shelter-mag. Sustainability goes beyond shipping containers and pre-fabrication. Lovers of true sustainability will have to look elsewhere. 400 pages, Hard cover wirh jacket, $45.00 EAN: 9781770854475 ISBN: 1770854479 www.fireflybooks.com

Acclaimed architect Peter Busby’ s new book shows a future where buildings and cities contribute to nature Peter Busby, the award-winning architect and winner of the 2014 RAIC Gold Medal, has been an innovator in sustainable building design since opening his architectural practice in Vancouver over 30 years ago. In his new book, Busby: Architecture’s New Edges, he directs his experience and observations to forecast a future in which architecture will create buildings and cities that will sustain life. Busby now works in the upper levels of international firm Perkins+Will which is perhaps THE leader in sustainable design and thinking. Some of the issues covered in the book are: Culture of Innovation: Fostering Ingenuity; Regenerative Design: Architecture Finds its Place in Nature; The Future of Cities: Sustaining Life; and The Future Face of HighPerformance Design. Peter Busby’s message is clear: “the architect can become an agent of change, capable of building things that guide others toward more responsible behaviour”, [but] ”We can-

not in good conscience exhort our clients to do things we ourselves would not do.” Busby walks the talk like few others in the sustainability movement - and ‘Busby: Architecture’s New Edges’ exhorts every one of us to do the same.

262 pages, 9”x11” 262 pages fully illustrated in colour, $49.95, ISBN 978-0-9827749-3-9 https://living-future.org/ecotone

PASSIVE HOUSE CONFERENCE October 1 and 2, Vancouver North American Passive House Network conference [NAPHN15] Hosted by the Canadian Passive House Institute [CanPHI] West at the Hyatt Regency hotel in Vancouver, the NAPHN15 conference features case studies of exciting Passive House developments, from low rise to high rise, in hot and cold climates, from North America and around the world. Workshops and presentations will be curated for those new to Passive House, and for others looking to deepen their knowledge. The two-day conference will focus on three key areas of Passive House design and construction: An Introduction to Passive House, Advanced Passive House Techniques, and Policy and Regulation. There will also be a trade show dedicated to exhibitors in the Passive House market. Post-conference tours in Vancouver and Whistler/Pemberton will showcase Passive House projects including a prefabrication plant and a public recreation facility. More details: http://naphn15.canphi.ca


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House in Low Off grid, passivelyheated home achieves LEED Gold

North elevation

When you’re a long way from the amenities of civilization, employing both active and passive solar strategies can provide security, independence and just good living in general. By Hillary Hosta

South elevation

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You’re invited …

to the Demo House Video Building Guide One of the best information sources on techniques and products for building high-performance housing in the Canadian climate. View the brief, informative videos, and return often as we add more.

http://www.ecohome.net/guide

A project of ecohome.net in partnership with ecoHouse Canada.

and

Canadian Directory OF Sustainable PRODUCTS SERVICES Find products and expertise for high-performance building http://sabmagazine.com/product-directory.html A dynamic web section for all your green building information

SUSTAINABILITY NEWS SUSTAINABLE ARCHITECTURE & BUILDING MAGAZINE

Building case studies - Technical articles - Events, seminars, product news

www.sabmagazine.com/sustainability-news.html S U S TA I N A B I L I T Y N E W S PA R T N E R S

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2015-07-06 1:53 PM


Beyond R-Values Study Shows There is More to Thermal Performance

The thermal performance of wall assemblies and insulation products has long been characterized using R-value, a metric which describes thermal resistance. While R-value is useful, it doesn’t tell the whole story about heat flow through building enclosures such as walls and roofs. Recently, a study by RDH has shown that real world thermal performance depends on a large range of factors including temperature, age, thermal mass, and surface reflectance.

By Lorne Ricketts

photo: Test roofs used to measure impact of three different roof membrane colours

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Beechwood Deep Energy Retrofit Post-World War II bungalow re-made for healthy, low-energy living By Steven Gray

This deep energy retrofit began with an uninsulated masonry bungalow located on a ravine lot with favourable solar orientation. The owners’ goals were to build an energy-efficient home with great indoor air quality and low water consumption while being respectful of their environmentally-sensitive site and integrating seamlessly with the surrounding building fabric. The resulting building, when modelled using Passive House software, has an annual heating demand of 30kwH/m2, approximately 65% less than a code-built home of equal size. Most remarkably for a retrofit project, the home achieved an air tightness level of 0.44ACH @50Pa. The main floor was completely opened up for more natural light and space flow [1]. The second storey was added for better energy efficiency and for less site disturbance [2].

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Standing seam cool metal roof

Garage deck

Natural cedar soffit Fiber cement siding

Site plan

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South elevation


IN

RE CA S N

NTIAL WIN E ID DIAN GRE N E A

PR O J E C T G BUILDING N

AWARDS

2015

The winning residential project of the 2015 Canadian Green Building Awards is a post-World War II bungalowtransformed into a highlyefficient two-storey home: a retrofit that exceeds Passive House airtightness requirements for new construction. The project underwent an integrated design process involving the architect, sustainability consultant, mechanical engineer, builder, and other professionals from the high-performance building industry.

Original house and outline of addition

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Urban Straw Bale Reno

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Renewed 90-year old Tudor-style home gets big energy cut Air tightness, improved insulation, new windows, reduction of thermal bridges, and ventilation based on Passive House principles reduce energy consumption by nearly 80%.

By Terrell Wong The graceful 90-year old masonry Tudor-style home, sitting mid-slope between the road in front and a laneway behind in the Beach area of Toronto, had changed little since its original construction. To honour this history, the beautifully panelled living and dining rooms were restored, and the spaces which wrap around these original rooms opened up. A full-width twostorey addition was constructed at the rear to create an open-concept kitchen and family room which look out into the lush sloping backyard through triple-glazed fullheight windows.

For longevity and life cycle costs, passive solutions surpass technological ones.A priority of the design was the continuation of the existing exterior stucco with the same robustness of the original masonry/ lime render construction but with a higher thermal resistance. Straw bale not only fulfills the structural but also the thermal and finishing requirements of the building. Straw bale is a double diffusion thermal mass system with the equivalent of R30 insulation. It is also economically more viable than solid masonry, and muchmore durable than stucco over a wood substrate. Although the original living and dining rooms were left intact, the entry and stairs of the original home were completely opened up with the new stairs extending into the basement allowing for natural light penetration from the back, front and side of the home. The entire house is within 7m of an operable window. Existing windows along the side of the building that had been covered over were restored to bring light deep into the interior.

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Vapour barrier paint over GWB

Project credits Architect Stone’s Throw Design Inc. Construction The Fourth Pig Worker Coop Mechanical Engineer Renu Building Science Structural Engineer Building Alternatives Inc. Commissioning Blue Green Consulting Group Photos Riley Snelling

Plywood over top of strawbale wall extend out to edge of soffitt and caulk at lime render

MATERIAL Straw bale construction for rear two-storey addition with lime plaster used as interior finish and exterior finished with breathable silicate paint; refurbished original house insulated in the roof with HeatLok Soya 2lb spray foam insulation by Demilec [targetting R60], and combination of HeatLok Soya spray insulation and Ultra Touch denim batts [from distributor Twin Maple] for the walls; air barrier sealed with SIGA tape distributed by Eco Building Resource; drywall with 99% recycled content, triple-glazed aluminum-clad wood windows installed on the street side custom leaded in the original Tudor style; new boilers and existing radiators relocated and used, in-floor radiant heating in new construction.

Straw bale: an air tight vapour permeable wall system also known as ‘vapour open’ or ‘double diffusion’

Air sealed window fastened to plywood box frame using air-seal tape 1” thick lime render finish 6ml poly taped seams under concrete slab

Plywood around window and door openings; air-seal tape around windows and doors

Custom prefinished aluminum sill with continuous drip edge

Section, new rear wall

Vapour barrier Air barrier

8 9 ´ The original wood trim and doors were catalogued and reused throughout the building, and the original radiators were refurbished and reused. ´ The existing kitchen cabinets were reused in the basement laundry room. ´ Many of the lighting fixtures were pre-owned. ´ A steel beam, taken from another heritage project, was used in the kitchen as a column. The contractors recycled all of the paper, metal and plastics. Our contractors routinely salvage wood, bricks and other usable materials from demolition for reuse in construction. The renovation gives the house a second life, and we anticipate that this type of reconstruction could occur in another 100 years. By limiting complex technology and concentrating on the thermal envelope, we reduced lifetime maintenance costs. Removing everything other than structure and insulation from the exterior walls will allow any future interior changes to not adversely affect the thermal envelope. v Terrell Wong is principal at Stone’s Throw Design Inc.

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Energy evaluations

can guide a renovation A major renovation, such as finishing a basement, installing new siding or replacing the heating system is also a major investment. With continually rising fuel prices, more and more homeowners are considering how to reduce their energy bills while planning renovations. They want to know where energy savings can be added into their renovation plans prior to making large changes to their home. An energy evaluation can provide this kind of valuable information, along with suitable recommendations for improvements. By Bridget O’Flaherty and Greg Furlong

Who performs an energy evaluation? A Certified Energy Advisor [or CEA] can guide the homeowner by conducting an energy evaluation. Certified by Natural Resources Canada to conduct energy evaluations, a Certified Energy Advisor is trained and experienced in many aspects of the building industry. They look at a house differently than a building inspector or contractor, considering it as a system for providing comfortable, affordable and healthy shelter to its occupants, otherwise known as “home performance”.

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The One Planet Reno in Ottawa, residential winner of the 2014 Canadian Green Building Awards. High insulation levels and air tightness were the starting points of the renovation. Photo: Christian Lalonde [1].

What is an energy evaluation? As thorough as a buyer’s home inspection, a certified energy evaluation provides details of a home’s current energy use and presents options for minor, major and deep retrofits for energy savings in a comprehensive analysis of energy performance. The evaluation includes measurements and calculations of a home’s geometry, detailed data collection on the building construction envelope and energy-using systems, and a blower door test to measure air leakage. All of this information is used to create an energy model of a home using approved software. The results gleaned from this model can then be used to determine heat loads, quantify air leakage and understand indoor air quality. A home’s energy usage is often solely attributed to its furnace. Although the type, efficiency and fuel used by a heating system are important factors, there is much more to a home’s overall performance. Compare this to a car, where

performance is not just about the engine, but about many features working together: aerodynamics, acoustics, glazing, drive train, electrical system and driver behaviour all influence how a car runs. The size and efficiency of the engine plays an important role, but it is only a part of a whole system; a driver’s comfort is affected by a combination all of these parts. A home has similar synergies. First, there is the building envelope, which includes the roof, attics, ceilings, walls, windows, doors, foundations, floors and insulation as well as the home’s natural air change rate [i.e. how quickly the air leaves, taking heat with it]. Then there are the high energy users [as with a car’s engine]: the HVAC systems, water heater, lights and appliances. Finally, an occupant’s behaviour can have a big affect on energy consumption – similar houses often receive very different utility bills!

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A CEA includes the blower door test to measure the air change rate [air leakage], the idea being to find the balance between improving air tightness and reducing heat loss while maintaining good indoor air quality [2 and 3]. Deep retrofits, such as gutting to install new insulation, windows and air barrier are best done by a professional [4].

During the energy evaluation, a home’s data is collected and a depressurization test [also known as a blower door test] is performed, providing not only the information needed to create an energy model, but also serving as a critical diagnostic tool for detecting major and minor air leaks and to assess indoor air quality. A home’s natural air change rate should be in a range that provides good indoor air quality and will determine how much added mechanical ventilation is required. A CEA estimates these air changes and makes recommendations to keep families comfortable and healthy.

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Once an energy evaluation is complete, a CEA identifies what needs attention, where to find the biggest gains in energy conservation, and how to prioritize upgrades among the building envelope and HVAC systems. For example, minor improvements, such as caulking, weather stripping and other airsealing, can often have a big impact on keeping the heat in and can be mostly done by the homeowner themselves. Larger retrofits, such as adding insulation or new windows, and deep retrofits, such as gutting, exterior insulation, re-siding, or adding a new heating system, will most likely require the assistance of a professional. After a home is properly sealed, it is important to determine the right sized HVAC systems to ensure overall comfort. This sizing can be based on the home’s performance as accurately determined by an energy evaluation. Lastly, occupant behavior

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will always influence overall energy use, and a CEA can give homeowners tips on ways to conserve energy and save money. A home is a place to feel safe and comfortable and renovations ensure these feelings last. Upgrading for aesthetic reasons may increase the overall value of a home, but including energy saving measures along the way increases it even more so. The advice received from an energy evaluation increases a home’s ROI [return on investment] and keeps money in a homeowner’s pocket long after a renovation is complete. v Bridget O’Flaherty and Greg Furlong are with the EnviroCentre, a local Ottawa-based environmental non-profit that helps residents, families and businesses save energy and money while reducing their impact on the environment. With a goal of greenhouse gas reduction, EnviroCentre focuses its efforts on improving building or home energy efficiency and sustainable transportation. To learn more, please visit: www.envirocentre.ca


RIGID FOAM PANELS ARE NOT ALL THE SAME Learn where and how they are best used With increasing attention put on thermal bridging in construction, rigid foam is finding its way into more and more homes, but which one should you use?

By Mike Reynolds

There are really three kinds of rigid foam panels you are going to have to choose from - Extruded Polystyrene [XPS], Expanded Polystyrene [EPS] and Polyisocyanurate [polyiso for short]. Before choosing, you should know exactly what you expect it to do, to make sure you walk away with the right one. They are all petroleum-based products but their characteristics, performance and ecological impacts vary significantly.

XPS - Extruded Polystyrene Rated at R5 per inch, but it will off-gas and lose a bit of performance over time. It will act as a vapour retarder [and become even less moisture permeable the thicker it is - 1 inch is about 1 perm, 2 inches about .5 perms]; when taped it can act as an air barrier; it does not absorb moisture, nor is it affected adversely by it. Note: 1 perm and 60 ng are U.S. and Canadian equivalent rates of permeability, below that rate of permeability classifies a material as a type II vapour retarder, suitable for residential construction.

XPS works great in pretty much any circumstance above or below grade, wet or dry. Regrettably, the hydro fluorocarbons [HFCs] most commonly used as blowing agents are far more damaging to the climate than those used with other rigid foam boards. Some manufacturers speak of a coming transition to less harmful blowing agents; that will be great news when it happens. HFCs have a global warming potential [GWP] that is 1,430 times more potent than carbon dioxide. The Kenogami House in Saguenay, Quebec. EPS solid insulation is used below the slab on grade and on the walls over the air/ vapour barrier. the air/vapour barrier is sandwiched between the wood frame and EPS exterior insulation.

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EPS - Expanded Polystyrene Rated at R4 per inch; it’s more permeable to air and moisture than XPS. Two inches of EPS has a moisture permeability rate of between 60 and 75 ng [1 to 1.25 perms], which is on the cusp of qualifying it as a type II vapour retarder, but on the more ‘breathable’ side of the scale. For reference sake, the traditional 6 mil polyethylene vapour barrier has a permeability rating of 3.4 ng, making it about 18 times more vapour resistant than building codes allow. The permeability of EPS can be handy at times if you want to add insulation to an existing wall assembly but are worried about trapping moisture, like retrofitting the exterior of buildings with additional insulation. Though to be absolutely sure you may be better with a mineral wool board which lets moisture pass right through. The lower R value of EPS compared to XPS is in a way compensated for by having a higher R value per dollar, as it is somewhat cheaper. If you’re not worried about losing an inch of space here or there, you’ll get a higher R value with EPS for the same amount of money, albeit with a thicker wall. The performance of EPS may drop slightly when it’s wet [reports I’ve seen indicate somewhere in the area of 10-15 %, so nothing too catastrophic], it will also dry out just as quickly as it got wet and return to its original performance. But there is nothing wrong with putting a little effort into keeping it dry if you can. The GWP of expanded polystyrene blowing agents is about 7 times worse than carbon dioxide, but that’s much less than the XPS.

Polyisocyanurate Rated at R6-6.5 per inch, but don’t count on that. Most insulations actually perform a bit better the colder it gets but polyiso breaks that rule. As of about 15°C its performance starts to deteriorate, and badly. By the time you get down to the -20s °C it’s nowhere near that. It can be a great product to use as long as you keep it warm, which is an odd thing to say about insulation. The news of its R value petering out when you need it most was a bit of shock that hasn’t permeated entirely through the building industry, so you still see it being installed occasionally on the exterior of walls. It won’t offer nearly the thermal protection you think it will in the dead of winter, and it may cause moisture damage due to its lack of permeability. Polyiso comes with a layer of foil on either side to keep the gases in, and at risk of straying off topic, that is worth talking about. Foil is a vapour retarder [or barrier if you prefer], so if you use polyiso on the interior of a stud wall, you won’t need to add an additional vapour retarder.

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And since there is foil on either side of the panel, you end up with a harmless second vapour retarder, but one that can help in summer months when there is a risk of the vapour drive reversing due to air conditioning during hot humid weather. Any inward-bound moisture would be stopped at that inner layer of foil, which will be warmer than the foil on the other side, so you reduce your risk of summertime condensation. That foil is the reason it can be problematic on the exterior, as you would be adding an exterior vapour barrier where you likely don’t want one. On the good news side, the GWP of blowing agents in Polyiso is similar to those in EPS, and in the right circumstances its R value is significantly higher, which deservedly or not helped earn it the reputation of being the ‘greenest’ foam. It can be a great choice when kept above freezing and away from moisture - so above grade for sure, and it makes a great interior thermal break when it’s kept a bit warmer by batt insulation in stud cavities. Being petroleum based should not result in foam being condemned by green builders on principle alone; it should be looked at in perspective. There are other great types of insulated sheathing [mineral wool and fiberglass to name two] and each will have their own benefits, drawbacks, carbon footprint and embodied energy through manufacturing, so even the greenest of the green will have some measurable impact. It takes energy to save energy, and manufacturing insulation is arguably one of the more noble things we currently do with fossil fuels. In conclusion: polyiso gets top marks for being ‘eco’ if you can handle its moody disposition. EPS is versatile and in the middle ground for performance, financial and ecological cost, and XPS is a top performer but comes with some unfortunate baggage. As soon as XPS completes its transition to less harmful blowing agents, I’m sure it will be welcomed into the green building community. v Mike Reynolds is a former home builder, a LEED for Homes Green Rater and the editor of Ecohome.net, the affiliate web site of ecoHouse Canada.


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