Insulate and Seal

This is Rob Dumont's home (see this pdf file) in Saskatoon, Saskatchewan. It was built in 1992, and it still stands as one of Canada's most energy-efficient homes. Rob Dumont was also involved in building the Saskatchewan Conservation House in Regina, in 1977. That was the prototype house that proved that the best building technique for cold climates is to build highly airtight, highly insulated houses.

So, when building a home like the Mill Creek NetZero Energy Home - that is, a cold climate home that produces as much energy over the course of a year as it consumes - the two most important steps to take are to insulate and seal it.


Rob Dumont often says: "Anything that has moving parts will fail; in fact, it must fail, because there is no such thing as a perfect bearing."

So, any component in a home that has moving parts will eventually cause you hassles. Also, it almost always consumes energy in order to work.

The beauty of insulation is that it is pretty much ageless. It saves energy 24 hours a day, seven days a week, and as long as it is kept dry it will never wear out.

I think that the best type of insulation is cellulose fiber insulation. It's made of used newspapers that are ground up and laced with a fire retardant (borax, I think). So it has an extremely low amount of embodied energy, and in fact putting it in the walls of a building that will last possibly hundreds of years is a form of carbon sequestration - the carbon in the newsprint will remain out of the atmosphere for the life of the home.

Peter Ameron of Habitat Studios is the builder of the Mill Creek NetZero Energy Home. As the pioneering leader of the Riverdale NetZero Project, he is the most qualified person in Edmonton to build this home. This is how he and his team built the Riverdale home's walls:

The idea is that you build a double wall - two two-by-four walls 16 inches apart (16 inches is 1/3 of a piece of plywood for the bottom and top plates). When the wall is filled with cellulose insulation, it has an insulating value of R56.

That's super insulation. No moving parts, saves energy 24/7, and lasts forever. The Mill Creek NetZero Home will use the same technique.


This is no-brainer. Air moving in and out of a building is probably the biggest waster of energy in the country.

Peter knows airtight:

"The builder, Peter Amerongen, has been sealing R-2000-equivalent houses for 20 years. Habitat Studio & Workshop uses an approach developed by Mr. Amerongen in the mid-1980s and written up in a Fine Home Building magazine in May 1994. This approach combines a variety of techniques and has been very successful in routinely sealing houses with complex forms without much fuss" (from the riverdalenetzero's technical section).

So you basically want to be living in a plastic bag, and then you provide fresh air to the house mechanically using a Heat Recovery Ventilator, a device that warms the fresh outside air with the stale outdoor air to recover about 80% of its heat before it's expelled.

Not Rocket Science

You'll notice that Peter's been sealing houses tightly since the 80s, and the date on the above-mentioned Saskatchewan Conservation House is 1977. In other words, we've known how to build super-efficient houses for a long time. Unfortunately, for the past 50 years we Albertans have been blessed/cursed with very cheap energy in the form of natural gas. Humans invariably waste what they have in quantity, it seems.

Those days are numbered now. Western Canada's natural gas production is on the decline. Where we will get our natural gas in 20 years is a mystery to me. Not much of it will be from our province.

So it's time to start building right. The Mill Creek NetZero Home is giving it a shot.

Repeat after me: "Insulate and seal...Insulate and seal..."

(cross posted at

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insulate and seal... insulate and seal!

I would check the fire retardent used in the insulation that you buy. Borax may be the best.It would probably ward off carpenter ants also. Some of the dodecacane fire retardants(if my memory serves me well)may be hazardous to your health. You should be able to get an MSDS beforehand on the particular fire retardent in the insulation that you are about to buy.

J Shaw

I'll do that. The River Dale NetZero Project guys are pretty diligent, so I have confidence that they've thought of this. Still, I'll check it out.

I'm adding an addition to my house right now and am trying to find the best product for insulating. All the contractors I am talking to say that fiberglass has a better R value than cellulose, but the soy foam would be best (or some foam/fiberglass combo? Recently, I have also seen a foil that you can place between the drywall and insulation to block radient heat. I haven't seen any mention of soy foam or the reflective barrier, what are your thoughts?

Yeah, insulate and seal- it seems to be the right thing to do under the current circumstances. All of your tips amazed me, I never seriously considered this aspect and now that I read about it I got a whole different perspective. I'm definitely in. I also did dome internet research and and I found a double glazing company UK that might do some good work with what I need. Thanks for everything!

With using spray-in-place foam, you not only air seal the building, it's a vapour barrier as well. It can be applied at 3-4in thick with an R-20 Value. It doesn"t matter how high your R-value is with cellulose insulation, it"s not completly air tight, therefore losing alot of energy.

With an air change rate of 0.5 air changes per hour at 50 Pa., this house will be as air tight or more airtight than almost any other, spray-in foam or not. With Peter Amerongen's special vapour barrier detailing, the airtightness is there.

Given that, an R-56 wall vastly outperforms an R-20 wall.

Do you have an airtightness numbers for the spray-in insulation? I do like that you get the vapour barrier and insulation in one go.

It's crucial to never underestimate the importance of an airtight seal for this type of insulation, otherwise a lot of energy is lost.

Thanks for the advice. Peter Amerongen has special detailing techniques for sealing houses. I hope to publish a piece on them later this year.

Need advise on insulating a large old type commercial building (Super Valu Store), which does not have a vapor barrier in the attic but has the insulation attached to the attic ceiling. The old insulation is now falling down and has to be removed which is another issue. Also, a large portion of the store has a four foot dropped ceiling and again the insulation is falling off the rafters. I have pictures. I need some professional advise. Can you help. Thank you.

Hi Ken,

I can't provide professional advice. Sorry. All I can do is urge you to insulate as much as you can afford once you do get a contractor lined up.


Hi Conrad,

Back at the design stage did straw bale ever cross your mind as a possible alternative? Similar to the insulation levels you will be getting but much different in regards to the 'seal' aspect. Seemingly uber-ecofriendly so I'd be curious to hear your thoughts.


Hi Brad,

I initially wanted to build with straw bales. The bales have such a low embodied energy that it was compelling for that reason alone. As I kept researching though, I began to realize two things: 1) there is no vapour barrier in a straw bale wall. Everything that we know about building science tells us that by the end of the winter that wall will be full of ice. 2) The R-value of a 16 inch straw bale wall would be closer to R25 than the R56 that we are definitely getting from our wall system. Furthermore, Peter Amerongen (who knows as much or more as any builder in Canada about building energy efficient houses) has told me that it's very difficult to seal a straw bale wall properly. So it wouldn't be as air tight as our wall.

Take care,


Just curious why you didn't use spray foam for insulation?

We'll achieve an excellent seal without it, avoid the much higher cost versus cellulose insulation, and avoid the higher environmental impact of foam versus cellulose.

Hi, Conrad.

I own a 1400 sqft bungalow in the Edmonton Mill Creek area and as with many houses in the area, mine is starting to show it's age, some 50+ years. When it is cold outside, my walls are cold to the touch and I can feel a cold draft around many of the exterior wall outlets. I have been considering having my house re-sided so that I can add a layer of insulation and possibly replace the windows.

As a first time home owner I am at a loss as to where to start.

How do I go about finding a contractor that can manage the work required in a manor that will be environmentally friendly, cost effective and last for another 50 years?

(PS: Great job with your site, plenty of good information and discussions.)

Thanks for the straw bale feedback Conrad. We have a family friend who has a bale house just east of Edmonton and every time we go there we fall in love with the idea. Did you find some studies, etc. that led to your concerns about the moisture freezing in the walls or was that a result of your own reading and/or discussions with others? It seems to make sense (in my layman's mind anyway) but I guess I'm still holding out hope there is a solution for our climate.

Also regarding the 'plastic bag' and HRV approach - I haven't read up on HRV technology much but it seems to introduce a single point of failure into the system. Is there any real concern with this (i.e. do you have to check it constantly to make sure it is functioning as intended) or not so much?

Thanks again.

Hi Brad,

I have no particular studies in mind. With regard to the HRV, it is a single point of failure, but there are many emergency back up solutions: the windows. I think that the building science is pretty solid in asserting that cold air moving into a house is undesirable.

I know what you mean about falling in love with straw bale houses - they are very beautiful.


While I can't help you with a contractor, I suggest that you think about using larsen trusses on your outside wall. The advantage is that you can take off your existing siding, then apply and seal a vapor barrier and then add the larsen trusses(2" x 3" joined with 1/4" plywood), creating whatever width of space that you want (I would suggest a minimum of 14" to give R42), put on siding and or plywood and fill space with cellulose insulation. Obviously you want to replace windows at the same time and increase overhang to accomodate wider exterior wall. You might also have to do something with roof to increase space for attic insulation. Another thing to do at the same time would be to insulate the exterior basement wall to 3' or 4' below grade. You can use styrofoam insulation and cover it with plastic stucco. While expensive and complex it is best solution that I have been able to devise.

Larsen trusses were created by John Larsen of Edmonton in the mid to late 1970s.

Hello there Rob I live in Alberta and we just bought a home that is 3yrs old it has a "bonus room over the garage" and we find it very cold in the winter months. it has two heat registers underneath the window which faces north. The exterior of the home is siding. and the real estate fellow who sold us the home advised that there is a house wrap on the underside of the siding all around the home.

The garage is insulated and drywalled but not heated. Do you have any ideas on how we can get this room warmer in the winter. Ohh yeah and in the summer months the room is alot warmer in the house.



If the siding is nailed through the house wrap, then the house wrap no longer acts as an air barrier. Here's a page that describes different air barriers:

I had a master br over garage in a previous house; similar problems to you. Not much you can do about the energy efficiency; it's a design problem. A typical room in a house has 2 cold surfaces (i.e. 1 wall & the ceiling). The bonus room has 3 cold walls & a cold floor & cold ceiling.

It would be good to learn more about the techniques PA uses for detailing the insulation installation.
Are you also recommending insulation firms?

On Feb 16, Conrad wrote
"1) There is no vapour barrier in a straw bale wall. Everything that we know about building science tells us that by the end of winter that the wall will be full of ice."
Although I am not a proponent of straw bale houses, I could not let the above statement go unchallenged. It is actually quite easy to add a vapour barrier to a straw bale wall by giving it a coat or two of latex paint on the inside. Air sealing is a little more difficult, but doable. As far as the ice in the wall...simply untrue. I am including a link to what I regard as some real building science regarding straw bale construction. The author is fellow Canadian, John Straube.

I do agree that the R value of straw bale walls (Straube reports values ranging from R26 to R30) is probably too little for our climate, but it is still twice what today's building code allows as a minimum. (whole wall R value of 2X6 wall filled with batt insulation is about R 13)

Hope you don't mind my challenge of your statements. I really enjoy your blog and hope to read more soon.

Considerate comments such as yours are always welcome here.

I guess that I was jumping to conclusions a bit with that statement.

However, the three strawbale houses that I've toured were finished with unpainted plaster on the inside, and the owners were practically boasting about how their houses "breathe". One person's "breathe" is another's "leak". They were explaining how air moves in and out of their houses as if it was a good thing, and they couldn't answer questions about that same air carrying moisture into the walls in winter.

Thanks for pointing me to a school of strawbale building that follows the rules :)

hello Conrad
having had some experience with cellulose over many years I would have some concerns with it settling in walls. Any thoughts?

Hi Les,

Rob Dumont built a similar house to mine (16" walls filled with cellulose) in 1992. Fifteen years later, he measured the temperature at the top of his outside walls and compared it to the rest of the wall - he found no difference. That, along with the fact that the manufacturer puts a binding agent in the cellulose and the assurances of my builder Peter Amerongen, lead me to feel very confident that there will be no settling of the cellulose insulation.


In the picture I see light through cracks between 2 sheets of OSB. Were these later sealed?


I don't think so. The cavity would have been filled with cellulose, and then the exterior covered with tar paper and stuccoed.

And the vapour barrier installed on the inside, of course.


My house has the same gaps in the walls. I assumed, but never did confirm with the framers, that this is to allow for expansion of the OSB if it gets wet. Almost everyone who visits the house comments on this. These gaps are covered from the outside by either tarpaper or Tyvek so the insulation can't leak out and water can't get in.


Conrad: I think your stucco finish is a big help for air infiltration.
Bob: the mfr recommends 1/8" space between panels. If this is done over blocking then air won't get in through the gap (not important for a stucco finish like Conrad's but very important for Vinyl siding)

I am an insulator in Alberta. What do you feel about the current code, and do you expect it to be changed much for 2010?

Hi Dave,

I think that the current code should enforce much higher R-values. As for how much it will be changed, I haven't the foggiest clue.


I wouldn't count on the current code changing any time soon. There's lots of pushback from spec builders trying to build as cheaply as possible. Where's the support for higher standards? Only a few "wingnuts" (to quote the leader of the province of Alberta during the "bozo" years). The general public would still rather spend their money on hot tubs and granite countertops than be forced to spend it on more insulation. Besides, natural gas is dirt cheap and will be for at least another year so why worry? Remember the controversy over changes to the fire code requiring better fire protection under vinyl siding? That likely went through only because it was related to safety (and probably had the support of the insurance lobby).


I think a double 2x4 wall with offset studs 24"OC, 10" thick with R12 & R20 fiberglass batts gives the best bang for the buck.
I've just posted details on my issues with dense-pack cellulose to my blog.

Has anyone tried to upgrade a ~25 year old building to airtight/superinsulation from the inside? I'm thinking I'd like to have the drywall removed, add 2x4s and perhaps a space and insulate with cellulose or fiberglass. My biggest concern is about integrity of the vapour barrier.

I used to teach an "energy and fuel science" course in the '80 an have been a huge fan of the Dumont style house ever since. I guess that makes me a "wingnut" retired physics prof. I've wanted a factor 9 home for some years now, but live in a four-plex that is administered as a condominium. I'd only be modifying the two outside walls and seeing if I can improve on the attic insulation.

Margaret in Thunder Bay


I'm trying to get my mind around how the actual double 2x4 framing was performed on site. Was it essentially a duplication of each wall layer on the deck, and the outer level lifted up and nailed to the 16" top and bottom plates before both were tipped up? Did you tip up the outer wall first and then the inner wall before attaching to the top plate? Was it a combination of both?

Thanks in advance for your reply.


On the same note for framing, conventional framing is done with 2 top plates, making a 3" thick bearing surface for the upper floor joists. With your method of a 16" wide OSB or plywood sheet on the top, what provisions are made to support the joists?

Hi Gordon,

Conrad is very busy right now so I've offered to answer your questions as my house (Belgravia NetZero) has the same 16" double-wall system.

Each wall is built horizontally as a complete double wall on the subfloor, then raised into place. From bottom to top, a wall consists of a 3/8" bottom plate, 1x4 spacer (3/4"), stud (7' 8 3/4" for a nominal 8' wall or 8' 8 3/4" for a nominal 9' wall), 2x4 (1 1/2"), 3/8" top plate and finally another 2x4 (1 1/2") giving a total wall height of 8' 1 1/4" or 9' 1 1/4". So yes, there are two 2x4's at the top of the wall with the OSB top plate between them.
Here are some pictures to illustrate how a wall is built and erected.

First, lay out the top and bottom plates side by side. This allows you to mark stud positions in the same location on both plates.

Position the bottom plate for horizontal assembly and toe-nail into place. The inside edge of the bottom plate will be the axis of rotation when the wall is erected.

Position the top plate and full-length studs.

Attach the full-length studs to the top and bottom plates

Frame in windows with 2x4's

Add OSB sheathing to the outside wall

Add caulking for the outside edge of the bottom plate

Erect the wall

Done! Repeat for next wall

Another view of erecting a wall, showing 2x4's on top of the top plate. This being a second-floor wall, the roof trusses will rest on these 2x4's.

Here's a SketchUp model illustrating how the 2x4's on the top plate tie walls together. The east wall (on the left) has been displaced 20" to the east. 2x4's that extend past the end of the OSB top plate are added after the wall is erected. In this example, the 2x4 on the outside of the south wall is 16" proud of the east end of the OSB top plate, while the 2x4 on the inside of the south wall is 3 1/2" proud of the east end of the OSB top plate. The 2x4 on the outside of the east wall is 3 1/2" shy of the south end of the OSB top plate, while the 2x4 on the inside of the east wall is 16" shy of the south end of the OSB top plate.


Excellent pics Bob.

In these and other pics of the double wall construction, I don't see headers for the window openings. Is that stage added later, or am I missing a framing trick?


Excellent question Al.

No tricks - headers are certainly required. The short answer is that the headers are in the interstice (joist space between floors). But I'm not partial to short answers so allow me to elaborate.

Here's the south main floor wall of Belgravia NetZero. There's no way you could lay joists directly on that top plate - there's nothing to transfer the load around the window openings.
BNZ Main Floor South WallBNZ Main Floor South Wall
So the headers go on top of the wall and the joists are attached to the headers with joist hangers. Header size depends on the size of the window opening. For the large living room window on the left, the header consists of 3 microlam beams, the dining room room window requires only 2 microlams and the kitchen window only a double 2x10.
South Wall With HeadersSouth Wall With Headers
Here the joists are attached to the headers.
South Wall With Headers And JoistsSouth Wall With Headers And Joists
Here's a view from the northwest showing how the joists attach to the headers.
View From NorthwestView From Northwest
Here's a photo. Sorry, this is the best I have.
Photo From EastPhoto From East
On the second floor, the windows go right up to the top plate so there's no room for a header in the wall even if you wanted to place it there.
BNZ Second Floor South WallBNZ Second Floor South Wall
In this case a full-width triple 2x10 header is used.
Second Floor South Wall With HeaderSecond Floor South Wall With Header
Here's how the roof trusses were designed to tie into the header.
Header And TrussesHeader And Trusses
Finally, a photo of the header and trusses.
Photo Of Header And TrussesPhoto Of Header And Trusses

This is excellent information, Thanks Bob. One more question: It appears that you will have very little in the way of a roof overhang. If possible, could you post a picture that shows what the final overhang will be?


Hi Ken,

Thanks for your question about overhangs. I'll try to put a response together soon.



Clearly I had used the wrong terminology, and should have said 'lintel'. However, you addressed exactly what I was curious about, and the framing technique used here is excellent info. Thanks. Al

In all the research I have examined regarding ‘building envelopes’, the evidence is clear that a well sealed home is necessary for energy efficiency. A solid vapor barrier and well constructed air barrier creates a best case scenario for insulation to do its job. For wall construction, these practices are relatively simple to complete.

However, I have not found any reference (in building codes or best practice recommendations) that the same effort should be made for ceiling insulation. It seems to me that the efficiency of the top (significant depth) of ceiling insulation is negated by the opportunity for air movement. Given that so much more insulation is recommended for ceilings, it seems to me that at least some effort could be made to improve the efficiency of that insulation.

I appreciate that due to the webbing nature of rafters, a solid air barrier would not be possible. It would also make sense that a (vapor permeable) barrier would need to be secured sufficiently to prevent ‘fold over’. And, clearly there would be more labor involved. But I believe in some ceilings it would be possible to cover a large portion of insulation for improved efficiency.

Does anyone have any experience with such an installation? Or, does anyone know a reason why such an air barrier should not be contemplated?

Great site, I appreciate the work it takes to keep it current, and the opportunity for discussion about the ‘common good’. Thank you.


Bob, I'd like to add my thanks for the drawings and photos.
I also thought of putting lintels above the top plate, but your way of doing it is better since it doesn't seem to require hangers (or were hangers added after you took those pictures).

Did you consider going with a single 2x4 top plate instead of a double?
Part9 allows single top plates when stack framing is used.


The drywall is the best air barrier in an attic. Cellulose insulation performs very well in an flat attic without an air barrier on top.

For walls an exterior air barrier is the best. It is easier to detail and it protects insulation from wind washing while an interior air barrier does not.

just thought I'd let you all know that I'm an insulator specializing in cellulose as well as walltite a medium density foam spray! Check out my websit for more info!! thanks. Doing a netzero home in athabasca!!

Hey there - I firstly want to say that this website is a great resource with all the detailed information that is provided. My husband and I are looking at building a new home in Edmonton, and although we don't have the means to build our own Net-Zero homes, we are looking to build at an Energuide rating of 82 or better.
I've been doing research intoinsulation spray foam insulation and discovered Enviro-Foam which is available here in Edmonton, is a closed cell foam and made from Soya oil and recycled plastic bottles and the only kind made with a zero-ozone depleting blowing agent. Here's a link with info on all the benefits

It has an R-value of 7 per inch - which means you could achieve an R38.5 value with 2x6 studs +R8 with rigid insulation on exterior to reduce thermal bridging. And this wastes much less space and materials than the 2' perimiter wall that your method requires. I'm wondering if anyone is aware of this product and or if they've used it? I would love to hear any feedback. Just as an FYI CMHC has tested the product and it is approved as an insulation, water and air barrier product in Canada.

Now about basement insulation - has anyone insulated the full exterior of their foundation? Did you use rigid or foam insulation? What about the basement floor? I want to know if it'll be worth it.



It has an R-value of 7 per inch - which means you could achieve an R38.5 value with 2x6 studs +R8 with rigid insulation on exterior to reduce thermal bridging. And this wastes much less space and materials than the 2' perimiter wall that your method requires. I'm wondering if anyone is aware of this product and or if they've used it? I would love to hear any feedback. Just as an FYI CMHC has tested the product and it is approved as an insulation, water and air barrier product in Canada.
Now about basement insulation - has anyone insulated the full exterior of their foundation? Did you use rigid or foam insulation? What about the basement floor? I want to know if it'll be worth it.

I attended a presentation by Peter Amerongen regarding reaching net zero at the lowest cost and someone asked about using foam. It I recall correctly, Peters answer was that the net zero house needed a true R56 wall and that spray foam wouldn't give that because of the thermal bridging of the 2x6 studs. The cost was also a factor as it is significantly more expensive than the using blown-in insulation. There was also a concern about the high amount of embodied energy in the spray foam compared to the blown in cellulose which is mostly made from recycled paper. Finally, despite the fact that the foam is rated as an air and water barrier, Peter said they had tried it and found the air-tightness of the foam to be disappointing. Peter also discussed how this "deep wall" system using 24" on-center 2x4s used only marginally more wood compared to a 16" on-center 2x6 wall. I'm not 100% certain but recall that the deep wall system uses only 16% (?) more wood.

Bob Heath, Thank you for the great pix and diagrams of your framing details. You mentioned that 2 x 4 plates were added above the OSB connector/spacer. Three ply headers were added above the plates. Are there any structural issues resting a 4.5 inch wide header on a 3.5 inch wide 2 x 4?

That is a great question Jim. Very few people would even notice that. I'm not a builder (though I did take a statics course many years ago), so I'll check with my builder (Peter Amerongen) before trying to answer the question in detail. One would think that there would be a torque toward the unsupported side of the header but nails on the other side of the header that hold it to the 2 x 4 would counter that torque (the three plys of the header are clinched together well so it acts as a single 4.5 inch member).


Regarding the bonus rooms, the best way to warm them is to insulate the floor joists with sprayfoam from the garage side. My cousins house had a cantaleiver with the same type of problem. The fibreglass insulation had settled and the floor vents were then exposed to the outside air. The two bedrooms above the cantaleiver were very cold. The vents would blow cold, and on really cold days the carpet along the wall would have frost on it. We reinsulated with sprayfoam (around the vents as well) and it fixed the problem.

Conrad, you don't know me and I don't really know you but I need to thank you. Your site inspired my wife and I to renovate our 1950 bungalow with a focus on making it as efficient as possible, on a fairly tight budget. We went from an energuide score of 62 on our 1950's bungalow in Red Deer to 81 (just found out today). Our utility bills are less than half of last year so far, and we did it all for under $25k. We sprayfoamed the whole house, replaced windows with triple panes, and replaced exterior doors. Without your site we couldn't have pulled it off, so thanks.

Conrad, you don't know me and I don't really know you but I need to thank you. Your site inspired my wife and I to renovate our 1950 bungalow with a focus on making it as efficient as possible, on a fairly tight budget. We went from an energuide score of 62 on our 1950's bungalow in Red Deer to 81 (just found out today). Our utility bills are less than half of last year so far, and we did it all for under $25k. We sprayfoamed the whole house, replaced windows with triple panes, and replaced exterior doors. Without your site we couldn't have pulled it off, so thanks.

Thanks Mike! I'm happy for you. And Energuide 81 is amazing. Kudos to you. I'm glad to have played a small part.

I am building a house this spring using pasive solar design and the double wall construction.
I am looking at using looking a using insulation batts with the outside wall insulation
running upright, the middle ones running sidways and the inside wall running upright. Will
this work? and is it to code?


Hello Rod,

Regarding your first question of using batt insulation with a double 2x4 wall: Habitat for Humanity built a net-zero house in Denver Colorado using that exact setup. As the designers had access to low-cost labour they decided to use batt insulation as it is "volunteer friendly". Check out

As for your second question, I believe the building code specifies a minimum level of insulation but not the type. If you have three layers of R12 you will be looking at roughly R36 (probably slightly less due the presence of the 2x4s). Since house are still being built with R20 batts in a 2x6 wall resulting in a total wall rating of around R18, you should easily meet the code requirements for insulation. Disclaimer: I'm not involved in the home construction industry and am not familiar with the specifics of the building code so you should research this further to confirm what I said.


To say cellulose insulation is green kind of sounds silly don't you think. To make the original paper was definitely not green, although some parts renewable, and it is really expensive to recycle and reship, so when energy costs soar we don't do it as much of it. Now urethane foam I hear has made great leaps in technology, base ingredients, and is the new generation blowing agent water? Foam applied properly can be a good insulator, but most energy savings are going to be in subsidizing the insulation and air stops in the ceiling. I think it has been said that 70% of the heat leaving your home is exiting through the attic air leaks. We need to concentrate on better air and moisture stops through out the homes and our energy costs would be affected positively I think. The expense of 24 inch walls seems a little crazy when 3.5 inches of foam is over R20. The jury is still out on how big the disconnect should be, and top and bottom are always connected.

Reasons cellulose is more environmentally friendly than foam:
1) It's re-using a waste product which means less paper is ending up in the landfill (or in Edmonton - in the compostor)
2) The original paper came from trees - a renewable resource - compared to urethane and polyurethane which are oil products.
3) Spray foam insulation is _very_ flammable. (At least it was when I did my house in 2008.)
4) Spray foam off-gasses although, as you point out, research is continuing on the use of different blowing agents.

The argument that increased energy costs will negatively affect recycling are doubly true for the production of a single-use product like spray foam that not only requires fresh feedstock but tanks, hoses and nozzles for each installation. Compare this to the blower used during cellulose insulation which can be reused hundreds of times.

It is true that foam has a higher insulation rating per inch that cellulose or batt insulation but it is also true that but unless you go with a double-wall design you'll still have significant thermal bridging at the studs. You say the expense of 24 inch walls is crazy but then compare them to a R20 wall but that's kind of comparing apples to oranges. If you want a net zero house in Edmonton's climate you'll need walls with insulation levels around R56 which would require over 9 inches of spray foam insulation - which would then still require some sort of double wall system.

What you say about controlling air leakage is true but as Conrad posted elsewhere on this site, his house has an air change rate of 0.36 air changes per hour at 50 Pa ( It is true that foam expands and fills small openings which might make controlling air leakage easier but Conrads house proves that air tightness and insulation material are really independent.

Reasons I didn't use foam in my house:
1) It's expensive
2) It requires a trained installer be hired
3) It off-gasses
4) It's flammable
5) Installers typically don't fill in every available inch with insulation but install a uniform level (of, say, R20) in all cavities

Did you use presure-treated lumber where walls meet the concrete? I have visited a few slab on grade houses (which mine will be for the most part) and some builders use pressure-treated lumber where the walls rest on concrete.

Is this necessary? Why or why not?

Many thanks again!

Mississippi John
Mississippi Mills, Ontario


I couldn't have said it better myself :)

Grinding up old newspaper is virtually free, energy-wise, vs. creating a brand new fossil-fuel based product from scratch.



Yes. That's what it looks like to me in these pictures anyway:

In answer to MississippiJohn's question regarding where the wood wall meets the concrete: No, I did not use pressure treated wood nor did I install any poly or thin foam sill sealer because 1) My house is 40 years old so the concrete is very well cured, 2) the (40 year?) old framing that I took out - which had been in direct contact with the bare concrete - had no signs of moisture damage or rot and 3) I did a test where I taped one square foot piece of poly to the bare concrete floor and left it for a weekend so see if any condensation would form underneath - none did. In my case I felt safe putting the wood on the concrete.

Having said that, if I was dealing with a fresh slab in a new home, I would definitely have bought a few rolls of sill sealer to put between the wood and the concrete. Here's what I'd look at using: FoamSealR Foam Seal Sill Gasket

As for using pressure treated wood: My feeling is that either sill sealer or pressure treated would be enough but that there's not a need for both.

Disclaimer time: I'm just some guy that renovated his house and installed a few solar thermal collectors and am definitely not an authority about construction methods.

Hope that helps.


Hello again - still proceeding towards a near netZero build in Lanark, County, Ontario. We have completed the plans and have requested quotes from three local, quality, green-friendly builders. Our initial results are that we are going to need to go back the the design phase to find ways to reduce the cost of the project - I'm 41 and I don't want to be paying my mortgage off at age 65!! So we'll likely reduce the size and do as much of the work as possible ourselves (kitchen, bathrooms, trim and doors, closets, etc).

One the the key areas the builders focus on is the double-wall - especially the insulation. But this is an area that do not want to compromise on. Unfortunately, there is no-one in the Ottawa-eastern Ontario region that I know of who is blowing dense-pack insulation into 15" wall cavities. There are a few who will do 6" stud walls, but not this type of application.

So I need to find a really good insulation specialist in the area and work with them to get them up to speed. Any thoughts or suggestions of contractors to contact would be really useful.

Lastly, for those of you who have done this, do you have a figure re cost per square foot of wall? This would be really useful in comparing against a more traditional wall.

Thanks, as always.

John Scime
Near Almonte, ON

Mississippi John
Mississippi Mills, Ontario


Have you tried O'Reilly Brothers in Ottawa or Warmth Insulation who are located in both Manotick and Maberly?



An Eastern Ontario contractor who has built straw bale and other green, energy efficient homes is Frank Tettemer. He is located on Mountain Doyle Road in Killaloe. He may either have experience blowing in cellulose or can recommend someone. Jim

John, Here's a good Q & A on the Green Building Advisor website.


Glad to hear that you're not compromising on your walls. Sorry, I don't have a per-square-foot wall price.

A few ideas on saving money:
-we have a south-facing bedroom upstairs with plenty of south-facing window. We added a westerly window to "even out" the light, but it was waste of money (and it is an ongoing waste of energy) because we almost never pull the drape on it back. In rooms with plenty of south glazing, consider not adding a second window.

-buy your light fixtures at a Rona or Home Depot type store - the lighting stores will literally charge you ten times more for the same type of fixture

-Kitchen cabinets? Ikea. Enough said.


I hope to build a net zero energy house in Montana in the next 12 months. Does anyone have an idea of the increased cost of construction - expressed as a percentage - over that of a standard 2x6 stick built? Also, and out of curiosity: would NZE construction work equally well in a tropical climate?TIA

Conrad might be able to help with some comments on the cost difference. Two comments regarding your question of tropical climates: 1) At this years Edmonton Eco Solar Tour, I talked to Andy Smith, one of the building engineers that worked on Conrad's house and he said that a good rule of thumb is to insulate the walls so that the R value is equal to the design temperature difference (the "delta"). In Edmonton, we design for -30 degree C winter days and if we use an indoor temperature of 22 degrees C the delta adds up to be 52. The recommended insulation level is R52. Obviously using this rule will give lower insulation requirements in more temperate environments. 2) In cold climates, we use vapour barrier to prevent condensation forming within the walls as warm, moist, interior air moves toward the cold exterior. From what I've read, the problem is reversed in tropical climates where the need is to prevent warm, moist, EXTERIOR air from moving through the walls to the cool, conditioned, interior. Other than the location of the vapour barrier, I believe the other construction aspects are the same.

Thanks for the quick response. Is the -30 C design temp an average low or the lowest recorded?

Hmm, that's a good question. The short answer is: I don't know.

The average low temperature in Edmonton in the coldest month, January, is -16 C / 3 F (from the table "Climate data for Edmonton City Centre (Blatchford Field) Airport" in According to that same table, the coldest temperature ever recorded in the city is -48.3 C / -54.9 F. As a long-term resident I know we sometimes get cold spells where the daytime "high" only gets to -30 C / -22 F although, at the risk of sounding like an old fart, less frequently now then when I was young.

Looks like it might be the median between the two. Still hoping that someone might chime in with a cost comparison.

I`ve always seen design temperature as being the worst temperature that can be expected in a region for an extended period of time.<

If your house can heat itself at -32 (our design temp.), then it will not fail, even if it may be colder for short periods of time.

As for cost, it`s an extremely difficult question. We only built our house one way - to have a very accurate comparison you would need to build the exact same house conventionally, and as a net zero project.

That said, we estimate that we made it 85% of the way to net zero (vs. a conventional house) for about $20,000 (Canadian dollars). The 20k was spent on insulation (16" walls), sealing the house extremely well, excellent windows, and passive solar design.

We think that the last 15%, the energy production portion, cost us about $55,000. That money bought us a 6 kW solar PV system and a substantial solar hot water system.

The 80/20 rule at work, it seems.


I am blowing in 32" of fiberglass insulation in the attic. Will the 5/8" sheetrock support it?
I've been reading that it will support 2.2 lbs per square foot.
My calculations show 1.3 lbs per square foot is what I will have.
Can someone verify?


Hi Mike - and Conrad,

I have a 1968 home, and am serious about improving the insulation to net ready- i.e. I'd like to target net zero if possible, and if not, then make reasonable decisions (so I'm studying all your info, as I am not a builder! I am an occupational therapist, and a student, and past the young family stage - but building for the environment and the future still makes sense to me!).

Anyhow, I live in Calgary, so you can imagine that I'm a fish in a desert. The quotes I get for windows (7 - 8) have been as high as $25,000 or as low as $10,000 (so deciding on quality is a big decision I'm working on), and then there is the insulation and siding (removing aluminum siding, adding quadlock and then hardy plank) which looks like about $50,000. . . . This doesn't cover my R2 door and other big-though well-sealed windows on the main floor.

So, my question to Mike is: did that price include siding? and if so, what kind? And to Conrad: how do I get insulation and windows for $20,000 - a completely reasonable and affordable expense.

BYW, I asked Peter for any contacts here in Calgary, but so far, he his office has not called back.

I'm trying to get as educated as I can before face to face talks - I hope - with some people who have achieved something like this here in Calgary.

Thank you - this is the most helpful, and hope-inspiring site I've seen - and makes me proud of the city I lived in so long.

Mary Anne

Hi Conrad,

Did you use tarpaper bc it is cheaper and more effective?

I remember my amazing-do-it-yourself uncle built his whole house with reclaimed products except the floorboards and wiring and the tar paper! That paper stayed on for a while until this amazing potter put the siding on. Sometimes I imagine doing all the quadlock insulation, then leaving it tar papered until the weather warms enough for stucco application.

My preference is stucco but every contractor here has guided me to hardi plank. Please accept my simple questions! I really appreciate this blog, and you! Still working on these decisions,

Mary Anne

Hi Mary Anne,

I don't actually know why the contractor puts on tar paper - sorry!

I would seriously consider hardi plank if we were doing it again. It's extremely durable, and I'm a bit disappointed with the stucco because the colour is running where it gets wet.


Mary Anne,

I believe that I mentioned $20,000 as an incremental expense. For $20k more than a conventional build, you can upgrade the sealing details, insulation and windows to get you 85% of the way to net zero.


This is great information.
With a wall system like this would you say that the cost is doubled? Or more like another 1/2 as much $$?

Thank you Bob for your ideas.

I have one question:

What is that tool, you are using for manual erection of walls?
Can it be bought on internet?
I´m from Czech Republic and we don´t use anything simmilar here.

Thank you wery much.



I think I've heard Peter Amerongen say 8% more, once your tradespeople are trained. Something crazy like that. Very little.



I'm not a carpenter so I asked Adam Larson, who framed my house, about the tool that you referred to. He said that they're called wall jacks and he suggested an internet search. Here are three possibilities:

Of these three, the first is most similar to what Adam uses and is likely the most economical.

It's nice to hear from someone in the Czech Republic. I have fond memories of cycling through Germany, Austria and Czechoslovakia (as it was known in 1985). Are you from Praha?


I'm surprised to hear that someone's going the stick-built route over there. I was under the impression that concrete and brick were the preferred materials in central Europe.

Any thoughts on reflective vapour barriers? This is a plastic vapour barrier which has an aluminum foil layer on it as well. Manufacturers claim that it can increase the existing wall insulation values by up to 20% thought I haven't seen any hard data to back this up.

What about the reflective double bubble insulation? They specify an R-8.5 rating for a 5/16" thickness when used on a wall and has the added benefit of being a vapour barrier. (

Hi Evan, reflective vapour barrier / insulation is only effective if it is not covered by another surface. Therefore, placing it behind drywall (intimate contact), or under a concrete slab reduces the R-value to that of simple bubble wrap alone (miniscule). Even when installed properly, once the surface becomes dirty/dusty, the emissivity increases and the benefit drops. Also, the quoted R-value likely relies on a standard temperature difference between the insulation surface and the surroundings - a value you likely won't have in your installation. In short, appropriate application of this insulation type is not generally found in the residential construction industry. Too many people do not understand radiative heat transfer, and therefore don't understand why it this product shouldn't be used.

Different ways to construct a double-stud wall:

In a post here dated June 2011, I lamented the fact that I could not find an insulation contractor in the Ottawa area that would confidently price a 15" dense pack application. 18 months later we still did not find the contractor who could do the job for under $6 per square foot. So I took a different tack in order to reduce costs and squeeze the project under budget.

I still have a double-stud wall, but I am using sheets of 5.25" type I EPS foam on the inside of the outer wall. I had heard from a few green builders in this area that they were buying used roofing insulation for insulating under slabs and pads. I managed to buy a truck load of this stuff for really cheap,that was originally on the roof of a hospital in eastern ontario, and am using it in the walls. With my labour, this brought the price from $26K to $10K. The wall is comprised like this - 1.125" BP R4 board (R4), 3.5" roxul (R14); 5.25" of esp (R21) and 4.25" of dense cellulose (R15). This puts me under budget, and with R51 walls. No doubt there are other ways, but this one works for us and really saved the project from a budget perspective. And we gained 70 square feet of extra space by mking the wall 13" instead of 15.5".

Our project is underway and can be viewed at if anyone is interested

Thanks again for all the information on this site!!

Mississippi John
Mississippi Mills, Ontario

I like system of Mr. Dumont´s house.
We have something like this but method is different.
Our construction:

I'm seeing lots of references to 16"/R-56 walls, but I seem to be missing roof/ceiling insulation info. TIA

The Riverdale NetZero project has 28" of cellufibre insulation in the attic which gives R100. Subsequent netzero houses by Habitat Studio & Workshop use slightly less - R90 or so.


Does anything need to be done to the ceiling spec to be able to handle 24"+ of cellulose? Can standard drywall and screws hold that kind of weight? It's probably been answered somewhere.

Special ceiling drywall is available: Ceiling Drywall

This site recommends screwing and gluing drywall when doing ceilings but they don't mention using ceiling drywall.


I'd appreciate recommended ceiling, wall and under-slab R-values for a design temperature of -10F for a NZE house.

I've heard the delta, or difference, between the outdoor and indoor temperature measured in degrees celsius can be used as the R value for the walls. -10F is about -23C so assuming the interior design temperature is +21C, you'd be looking at R44 walls.

Based of some of the houses in Edmonton, a _very_ rough target for the ceiling would be 150% the R-value of the walls - or roughly R66 in this example. Under-slab insulation would be 1/3 that of the R-value of the walls - or roughly R15 in this example.

Having said that, I'd suggest doing some proper modelling rather than using a rule of thumb for the insulation levels.



Thanks for your site...very useful information! I am a modular builder just outside of Edmonton and we are going to be building a double walled modular home. Our plan was to do build two 2x4 walls with off-setting studs and use fibre-glass batte insulation with 3/4" space between the walls.

Although I realize its not as good as the blow-in cellulose, due to size restrictions, we are thinking this is the best way...can someone please comment on this and/or give me advice on what they would recommend?

Thanks for your help in advance.


Hi Lucas, Thanks for your question.

It is true that a 16" wall takes up a lot of space, especially on a narrow lot. For a thick wall like that a relatively low R/inch insulation like blown in cellulose works well and is cost effective. For thinner walls like you are looking at there are a lot more options. Some way of cutting down on the cold bridging is a good idea. Your off-set studs do that and it is much better than 2x8 studs.

Fibreglass batts are not very dense and allow quite a bit of airflow (taking heat with it) through them, both horizontally and vertically. I would recommend a denser batt insulation, like Roxul ComfortBatt. It is R14 for 3.5". Roxul is much denser than fibreglass and holds its shape very well. It is much easier to install well without leaving empty areas, which is a major problem with fibreglass.

You mention that you are putting a 3/4" space between the inside and outside walls. If I understand that correctly the total wall thickness will be 7 3/4". I don't see any benefit in doing this if you put two layers of 3.5" batts in the wall. In fact, an air space between the two walls is counterproductive. The function of insulation is to create air pockets that stay in place and prevent airflow from moving heat through the wall. Air is still the main insulator. An air gap would allow convection currents to develop inside this gap, taking heat from the bottom to the top and across the gap (similar to convection between panes of window glass).

I built my own house with 7.5" wall using a different method. I framed using 2x6 studs and put 2 inches of polyisocyanurate foam board insulation on the outside (no wood sheathing). The foam board cuts down on the cold bridging. Nominal R value is R22 for the batts and R13 for the foam, a bit higher than two 2x4 Roxul batts. The foam on the outside may make it a more difficult to put siding on.

Finally, depending on the outside finish of the house, frame at 24" centres if you can.

I hope this helps. Feel free to ask any more questions.

Philip Mees

Thanks Philip!

We will likely go with the Roxul. Thanks for the info on the gap in the middle...I thought that it would be better because I assumed it would be a dead air space but as you said, it likely wouldn't be due to the poly being on one side only...good point.

Due to the nature of our construction (modular), we sheet and glue the exterior walls on both the outside and the inside...We considered the Styrofoam on the outside but the exterior cladding product we are using for the build is the KWP composite dutchlap siding...we had no way of properly fastening it to the studs with the foam in the way(which you pointed out) and gluing each piece seemed like it would be too much work.

We have decided to increase the wall thickness to 12", frame 2' O.C and use cellulose in between the walls. We are excited about this because the nature of our modular homes (rectangular, bungalow style, simple roof lines etc.) lends well to energy efficiency.

I'm happy I found this forum before we started to frame the house as it changed the way we were planning on doing it.

Thanks again for your help!


Correction: I wrote that message in two bursts...We will NOT be going with the Roxul but rather the cellulose...haha...

Sorry about the confusion!


I was doing some reading and according to recommendations by Qualistat in Calgary, any ceiling insulation above R50 improves the Energuide rating marginally.

Does anybody have any insights on Energuide ratings and their relevance?

Here's a link you may find interesting...


What's the name of your modular home company? Do you have a web site that shows any of the details of this new project?

Hi Ken,

Our company is Wesland Modular Homes. We are based in Evansburg, which is about 1 hour west of Edmonton on Hwy 16 (past Spruce Grove and Stony Plain). Our website is and we are on Facebook as well. We will be uploading pictures and descriptions on both our website and Facebook.

We are excited to build this home...we are also handling the site work for this customer (i.e the foundation, the garage, the mechanical, the services so we will be able to do some testing on the home to see how it performs vs. conventional buildings ( built to current building codes).

You are also welcome to visit our facility to have a look if you'd like to see it firsthand. As I mentioned we are right on highway 16 toward Jasper, about 1 hour west of Edmonton.


Here is a link to our Facebook page with some pics of the current project we are doing that is using the 12" double wall system. Enjoy!!/media/set/?set=a.328612143918599.77660.166631920116623&type=1&notif_t=like

Copy and paste the link into your address bar to go to the page.

Also, feel free to "like" the page if you want more updates on this (and other) modular projects we are doing.

Wesland Modular Homes


I've been reading more about blowing in cellulose insulation into walls and I have a question to ask the forum:

Should I add water to the cellulose insulation to prevent settling? Keep in mind, we are doing the double wall system and we are not adding a top plate between the two walls; the thought is that if the wall cellulose settles, it will be fed by the ceiling insulation (which will be cellulose). That said, I'm still concerned about the cellulose below the windows.



We have purchased some acreage with a fairly high water table. Our prospective contractor has recommended building slab-on-grade. Since we plan on building Passive House/Net Zero Energy, there will be a fair amount of mechanicals which I'd much prefer not looking at on a daily basis. Is there a method of building a basement which will keep water out?

Lucas, it was recommended to us to have the cavity filled with borate treated, damp-spray cellulose. That should eliminate any settling.


How did they blow the cellulose in? Was the poly applied first?

We are planning on doing this soon so any insight to the procedure would be really helpful...

Thanks again!



Did you see the pictures here?


Hi Conrad,

Thanks for the link...

I was planning on trying to blow in the insulation from the top of our 8 ft wall. Due to the nature of our buildings (very simple, rectangular boxes with 8 ft wall), I think this would be the fastest and simplest way to do it...just like concrete walls.

Is it special insulation we need or can we use conventional blow-in and add stuff to it?

I appreciate your help with this...


Quick update:

We contacted L.L. Climatic Insulation Ltd. and they installed the blown-in cellulose wall-bar insulation into the wall. The application is different than standard ceiling cellulose. Its dampened to create structural integrity within the cavity to prevent settling.

They did a great job. With our buildings we apply 3/8" sheeting on the interior of the exterior walls (to increase building rigidity) so I'm not worried about drywall pops at all.

We are going to post pics on our


Lucas, how thick are your walls? We're planning on going the Passive House route, so our walls will be around 16" thick. I would like to use dampened cellulose to prevent settling, but the contractor has misgivings about this because it would take too long to dry.

Our walls are 12" thick (O.S). As far as the dry time, I didn't slow us down at all...mind you we build 6 at a time so there are often "breaks" in between stages.

Good luck!


Just an update...its been an interesting Spring 2013...we've sold 2 more homes featuring the "double-wall" system. We featured it on our website and we've actually had inquiries!! Also, I've had 3 customers say that they were looking for this type of wall system. I think its catching on!


Thanks for all the information. I haven't seen anything mentioned yet about sound insulation. I would assume that a house built with walls and windows as you are suggesting would have much better sound insulation values than a typical build. It would be interesting to know the difference.

Hi Ken...our company is Wesland Modular Homes and our website is

Conrad: Those pics are pretty sweet...looks like an interesting and expensive project.

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