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The History of the Chainsaw Retrofit

The first deep-energy retrofit was performed by Canadian researchers

Posted on Aug 14 2009 by Martin Holladay, GBA Advisor

To achieve the carbon reductions needed to prevent a global ecological catastrophe, almost every house in North America will need a deep-energy retrofit. If the projecting elements on a home’s exterior — especially the eave and rake overhangs — can be stripped away, the best retrofit option is to wrap the exterior of the house with an airtight membrane and a deep layer of insulation, followed by new siding, roofing, and windows.

Because the purest version of this insulation technique requires a building’s roof overhangs to be lopped off, the method is referred to as a “chainsaw retrofit.”

It started In Saskatoon

The chainsaw retrofit technique has a precise point of origin. The method was pioneered by two Canadian energy researchers, Rob Dumont and Harold Orr, who cut off the eaves and rakes of a modest ranch house at 31 Deborah Crescent in Saskatoon in the summer of 1982. The work was funded by the Institute for Research in Construction, a branch of the National Research Council Canada.

Dumont and Orr are both retired. As the first generation of building scientists and residential energy researchers gets old enough to pass the baton to younger practitioners, it’s important to remind today’s young architects and builders of their ground-breaking work.

Prairie pioneers

Dumont and Orr were key members of the research team that designed the Saskatchewan Conservation house in 1977. Five years later, the two engineers set about to develop a technique for superinsulating existing homes.

In retrospect, it’s clear that Dumont and Orr were the first to combine a number of elements that have become part of the standard procedure for deep-energy retrofits. The work at 31 Deborah Crescent included the following steps:

  • The existing siding and roofing were stripped from the house.
  • The house was wrapped with a tight new air-barrier membrane.
  • A thick layer (R-43) of insulation was installed on the exterior side of the wall and roof sheathingMaterial, usually plywood or oriented strand board (OSB), but sometimes wooden boards, installed on the exterior of wall studs, rafters, or roof trusses; siding or roofing installed on the sheathing—sometimes over strapping to create a rainscreen. .
  • New siding and roofing were installed.
  • All of the windows were upgraded.
  • A heat-recovery ventilator (HRV(HRV). Balanced ventilation system in which most of the heat from outgoing exhaust air is transferred to incoming fresh air via an air-to-air heat exchanger; a similar device, an energy-recovery ventilator, also transfers water vapor. HRVs recover 50% to 80% of the heat in exhausted air. In hot climates, the function is reversed so that the cooler inside air reduces the temperature of the incoming hot air. ) was installed.

Did they really use a chainsaw?

In August 1982, the retrofit work began on the 1,200-square-foot house at 31 Deborah Crescent, described by the researchers as “a bungalow built in 1968.” As it turns out, the remodelers never used a chainsaw. “We used a circular saw to cut the framing — the cut was about 2 1/2 inches deep,” Orr told me recently. “We finished the cuts with a handsaw. When I started giving presentations about the house, numerous people said, ‘You should have used a chainsaw.’ So I started to call it the ‘chainsaw retrofit’ job.”

In their research report, Dumont and Orr wrote, “In order to allow a continuous air-vapor barrier at the junction between the wall and roof, and to avoid having to wrap the existing eaves and overhangs, it was decided to remove the eaves and overhangs. To accomplish this, the plywood soffits were removed, and the shingles were removed from the eaves and overhangs. A power saw was then used to cut through the roof sheathing and part way through the roof truss eave projection and roof ladder in line with the outside of the existing wall of the house. … Finally, the saw cut in the trusses was completed with a hand saw.”

Fiberglass or foam?

These days, most builders specify rigid foam or spray polyurethane foam for a deep-energy retrofit. Back in the 1980s, however, Dumont and Orr used fiberglass batts, in part because the researchers were under strong pressure to keep expenses to a minimum. “The problem with polystyrene is that it is four times the price of fiberglass,” explained Orr.

At 31 Deborah Crescent:

  • Workers removed the stucco, eave overhangs, rake overhangs, and asphalt shingles. At the roof perimeter, gaps between the roof trusses were covered with a strip of 3/8-in. plywood.
  • The roof sheathing and wall sheathing were covered with 6-mil poly, held in place with plywood strips. All of the seams in the poly were sealed with Tremco acoustical sealant.
  • A frame of 2x8 purlins (installed on edge) was built on top of the plywood strips.
  • 2x4 rafters were installed over the purlins. The rafters were connected at the ridge with galvanized strapping. The new 2x4 roof framing included new overhangs at the rakes and eaves.
  • Two layers of fiberglass batts were installed on the roof: 8-in. batts were threaded under the rafters, and 4-in. batts were dropped between the rafters.
  • New plywood roof sheathing and asphalt shingles were installed over the rafters.
  • New 2x4 wall studs were hung from the projecting rafters and toe-nailed into a wide bottom plate that was secured to the house with galvanized strapping. The 2x4 studs were positioned to create room for 12 inches of fiberglass insulation.
  • Window rough openings were lined with plywood, and the new window sills were covered with painted metal flashing.
  • The space between the old wall sheathing and the back of the new studs was filled with horizontal 8-in. fiberglass batts. Then 4-in. batts were installed vertically between the studs.
  • The walls were covered with new plywood wall sheathing and stucco.
  • The existing basement slab was covered with 3 inches of polystyrene.
  • The basement walls were insulated on the interior with 12 inches of fiberglass behind and between new wall studs.
  • Storm windows were installed to provide a third layer of glazingWhen referring to windows or doors, the transparent or translucent layer that transmits light. High-performance glazing may include multiple layers of glass or plastic, low-e coatings, and low-conductivity gas fill..
  • An HRV programmed to provide 0.5 air changes per hour was installed.

Spectacular results

Although builders in warmer climates might hesitate to wrap a house with polyethylene, the technique works very well in Saskatoon. “Wrapping the exterior of the entire building with a polyethylene air-vapor barrier proved to be a very effective method of reducing air leakage in the building,” the researchers reported. “This particular house, after retrofitting, proved to be the tightest house in Saskatchewan measured to date by the National Research Council. … The air leakage of the house as measured by pressure tests was reduced from 2.95 air changes per hour at 50 pascals to 0.29 at 50 pascals, a reduction of 90.1%. Before and after measurements were taken of the space heating requirements of the house. The design heat loss of the house was reduced from 13.1 kW at -34°C to 5.45 kW by the retrofit.”

Twenty-seven years later, the house at 31 Deborah Crescent remains in excellent condition, and Orr reports that the fiberglass used to insulate the basement walls has stayed dry. “I talked with the homeowner just last year,” Orr told me. “He said the house is very comfortable.”

How much did it cost?

The experiment at 31 Deborah Crescent was controversial at the time. “The people in Ottawa thought this was way too radical and costly,” Dumont told me recently.

According to the research report, “As the retrofit procedure involved major alterations to the entire envelope of the structure, costs for the total retrofit were high. The total cost for the project, which included upgrading the shingles and the stucco on the house, was $23,700 in 1984 dollars.” In 1984 U.S. dollars, the cost of the work was $18,230; in 2009 U.S. dollars, the cost is equivalent to $37,510.

To modern readers, the investment sounds like a bargain. These days, most deep-energy retrofit jobs are far more expensive — in the $50,000 to $100,000 range.

Ripples far and wide

Dumont and Orr’s research findings were influential. When a Massachusetts engineer, J. Ned Nisson, learned about the Saskatchewan Conservation House, he was galvanized into action. “I invited Harold Orr and Rob Dumont to Massachusetts, and we started running workshops,” Nisson recalled recently. “The workshops were wildly popular.”

Nisson went on to found a monthly newsletter, Energy Design Update, in 1982. With co-author Gautam Dutt, Nisson wrote a landmark book, The Superinsulated Home Book, published in 1985. The book became the bible of the shrinking band of residential builders who carried the energy-efficiency torch through the dark years from 1986 to 2004.

Looking ahead

The global climate crisis now compels our country to face a Herculean task — performing deep-energy retrofits on most existing buildings. “In construction, making decisions is not like solving a mathematical equation,” Dumont told me. “The economics are changing all the time: labor, materials, and energy costs always change. We have nine million existing dwellings in Canada, and over the next three decades I can see virtually all of them being retrofit. Many of the older buildings have wood siding or something that needs renewal periodically, so it makes sense to combine the retrofit work with the renewal of the exterior siding.”

Not all existing buildings are good candidates for chainsaw retrofits. If a historic building is decorated with elaborate, irreplaceable exterior trim, retrofit workers will probably leave their chainsaws at home. But the technique works well on simple ranch houses with plain trim. If you drive around your town with a “chainsaw retrofit” eye, as I do now, you’re likely to spot entire neighborhoods ripe for a skilled crew equipped with gas-powered Husqvarnas.

For more information on the first chainsaw retrofit, see the research report by Orr and Dumont, “A Major Energy Conservation Retrofit of a Bungalow.”

Matt Wasse of Herrison Architects in Seattle has created a video animation of a chainsaw retrofit using Larsen trusses filled with dense-packed cellulose insulationThermal insulation made from recycled newspaper or other wastepaper; often treated with borates for fire and insect protection.. To see the video, click this link.

A GBAGreenBuildingAdvisor.com video of a recent chainsaw retrofit job — including footage of workers cutting off roof overhangs — can be found here: Video Series: Exterior Insulation Retrofit.

Last week’s blog: “Getting Insulation Out of Your Walls and Ceilings.”


Tags: , , , , , , , , , ,

Image Credits:

  1. Harold Orr
  2. Institute for Research In Construction
  3. The Superinsulated Retrofit Book by Brian Marshall and Robert Argue

1.
Fri, 08/14/2009 - 06:14

chain saw retrofit
by Ron Brenner

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Overhangs help to protect the walls and windows from rain and snow; reducing wear and tear and keeping your home dry. Overhangs help to control the sun, keeping you comfortable. Overhangs and eaves add character to the home. Overhangs are good!


2.
Fri, 08/14/2009 - 06:19

Of course overhangs are good
by Martin Holladay, GBA Advisor

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Ron,
Please read the blog again and look at the photo. Of course overhangs are good. The overhangs are lopped off for one reason only: to facilitate the installation of a tight air barrier on top of the exterior wall and roof sheathing.

As I wrote in the blog, "The new 2x4 roof framing included new overhangs at the rakes and eaves." Note also the photo caption: "Although the home’s roof overhangs were lopped off during the energy retrofit work, the eave and rake overhangs were restored when new roof framing was installed on top of the original roof."


3.
Fri, 08/14/2009 - 09:26

Not just for retrofit
by John Brooks

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Chainsaws and Lopping off the overhang conjures up a strong image.

Visualizing new enclosures without the "roof cladding layer and overhang" leaves a very clean alignment of the control layers.

Then "cap it" with the roof layer including ample overhang.

A Hat for the House.

The Picton Brothers LEED project among others employ this concept.
It also seems to be widely used in Euro Passivhaus projects.


4.
Fri, 08/14/2009 - 10:14

History of the chainsaw retrofit
by Harold Orr

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"At the roof perimeter, gaps between the roof trusses were filled with blocking." Should read: "At the roof perimeter, the ends of the existing rafters and gaps between the rafters were covered with a strip of 3/8" plywood."


5.
Fri, 08/14/2009 - 10:37

Hello, Harold
by Martin Holladay, GBA Advisor

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Harold,
I have made the correction you noted.

Thanks for visiting; thanks for your correction; and thanks, of course, for your trail-blazing work!


6.
Fri, 08/14/2009 - 16:19

Superinsulated Retrofit Book
by Dark Lad Slim

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Hi Martin,
Great article. I presume that you've come across "Super-Insulated Retrofit Book: A Homeowner's Guide to Energy-Efficient Renovation" by Robert Argue and Brian Marshall? Another great book from 1984/84. Can't remember if it features 31 Deborah Crescent though.


7.
Sat, 08/15/2009 - 05:03

I haven't seen the book -- yet
by Martin Holladay, GBA Advisor

Helpful? 1

Dark Lad Slim,
No, I haven't seen the book. I just found a used copy ($17) on the Web, and I ordered it. Thanks for the suggestion. (I noticed, however, that one anonymous Web reviewer had this to say about the book: "While this book was well done, and good for its time, the strategies for superinsulation and air sealing have improved greatly, I found this book of very limited value, Some of the techniques promoted are obsolete. One should consult other works as well if one is considering this kind of approach.")


8.
Sat, 08/15/2009 - 14:24

Super-Insulated Retrofit
by Dark Lad Slim

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Yes, the detailing can be improved and may be obsolete in some cases but it has some excellent suggestions and it's a huge leap on from the standard home retrofit - even by contemporary standards (excluding advanced concepts such as PassivHaus retrofit of course).

Having now checked I find that it was written in 1981, since then our understanding of building physics has advanced and whilst many concepts that are discussed remain true the devil is at ever in the detail and this could now do with some revision. To this end the book still has merit but should be regarded as an excellent starting point rather than an end point.


9.
Thu, 08/27/2009 - 14:26

The first mention of the chainsaw retrofit technique
by Martin Holladay, GBA Advisor

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Dark Lad Slim,
The book you suggested is indeed interesting. On page 58, I find the first recorded mention of the chainsaw retrofit technique: "[A] substantial overhang might pose problems as the [exterior insulation retrofit] job progresses. Before installing the vapor barrier, it might be advantageous to cut the roof rafters back to the level where the new curtain wall will extend."


10.
Tue, 09/15/2009 - 15:54

yup!
by Anonymous

Helpful? -1

This is without question the best way to insulate a home or building. It is ironic that we still build new homes the old 'inefficient' way.

As much as I love and advocate for this or the PERSIST method for retrofits, I struggle with the practical application from an aesthetic standpoint. (Yes, Martin I know, "It is all about Energy") Perhaps in rural Canada, where homes like the one in the photo are passable, this makes sense. But, here in a city filled with historic homes we have to include exterior trim and other details that give the house a sense of scale, proportion, architectural beauty, and aesthetic integrity.

Is there a good solution? Would you be willing to share the section detail with your readers? (Assume that we don't want to build an entire second wall outside the house and stuff it with fiberglass like your story)


11.
Tue, 09/15/2009 - 15:55

Yup! plus
by Michael Anschel

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Didn't mean to post anonymously.


12.
Wed, 09/16/2009 - 04:23

You're right
by Martin Holladay, GBA Advisor

Helpful? 1

Michael,
As I wrote, "Not all existing buildings are good candidates for chainsaw retrofits. If a historic building is decorated with elaborate, irreplaceable exterior trim, retrofit workers will probably leave their chainsaws at home. But the technique works well on simple ranch houses with plain trim."

So you're right — historic buildings often pose a dilemma to those contemplating a deep energy retrofit. As with most remodeling questions, there is no single answer to this dilemma. Remodellers must be knowledgeable, adaptable, and ingenious. Also humble — because it is sometimes necessary to admit that there is no perfect solution; compromise is sometimes necessary.

Here's my summary:

1. All deep energy retrofits are expensive.

2. If you have a historic building with a beautiful, hard-to-reproduce exterior, you will probably be unable to achieve deep-energy-retrofit savings without sacrificing significant amounts of interior space.

3. If you can't do everything, start with the important things that you CAN do. The first step is always air sealing. Foam the basement rim joist and climb into the attic with a foam gun. Then call the blower-door contractor and continue as long as necessary, performing blower-door-directed air sealing.
The next step is to install deep attic insulation. Then address basement moisture issues and install basement wall insulation. Next — assuming that your local Historical Preservation watchdogs allow you to — replace the windows with good low-e triple-glazed units. If Hysterical Preservation concerns prevent this, negotiate whatever compromise is possible (usually storm windows of some kind, either exterior or interior).


13.
Sun, 10/17/2010 - 19:45

Chainsaw retrofit
by Harold Orr

Helpful? 0

I have been involved in another chainsaw retrofit and my son did a time lapse of the chainsaw part. See http://www.youtube.com/watch?v=Kp4cBUXnH-k . We have insulated the roof by installing a 6mil poly vapour barrier, 6" wide strips of OSB to hold the poly in place and 2x8 strapping at 4' OC parallel to the roof edge, then 2x4 rafters. The space created is filled with three layers of R14 insulation. 1/2" plywood sheathing, with "Tyvek" as a temporary roof covering with the final roof a galvanized sheet metal shingles. I tried to create a time lapse of the insulation process without success.


14.
Wed, 05/04/2011 - 14:13

An e-mail from Rob Dumont
by Martin Holladay, GBA Advisor

Helpful? 0

Rob Dumont just sent me an e-mail:

"Hello Martin:
Thank you for writing up the chainsaw retrofit project. Harold was the brains; I was the pen.
It is interesting that the commercial folks now use the same type of approach (air/vapour barrier outside of the structure of the roof and walls), but on new construction, because it does such a good job of air and vapour sealing.
Cheers,
Rob Dumont"


15.
Thu, 11/15/2012 - 12:03

Edited Thu, 11/15/2012 - 12:04.

A video interview with Harold Orr
by Martin Holladay, GBA Advisor

Helpful? 0

A recent video interview with Harold Orr:


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