Lstiburek’s ideal double stud wall
user-1194932448
| Posted in Energy Efficiency and Durability on
Why do I see all these high R value walls that seem like they would be absolutely hell to build in a rainy windy environment. There seems to be way to much assuming that the weather is good while building. I live in coastal Alaskan climate with close to 200 inches of rain a year and high winds when it rains. Lstiburek’s Ideal double stud wall doesn’t even look like you can build it from the outside in which is the main appeal of double stud is you would be able to have the siding on and sealed in before adding any of the insulation is added. Am I the only one from a building perspective this looks like a terrible plan.
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Replies
User ...448,
It's not just walls. A lot of details for floors on piers, and roofs with exterior insulation suffer from the same weakness. The results are great, but the process to get there seems fraught with difficulties.
It brings up an interesting discussion: Maybe some building assemblies should be chosen based on climate, not because they are suitable when complete, but because in some places they are almost impossible to get to that point?
Lstiburek also has the "ideal wall", which is more for far northern climates, and it has ALL the R value on the exterior using rigid insulating materials.
I don't see why a double stud wall couldn't be built in your region though. Frame the wall, but up the exterior sheathing, then insulate from within. Only the exterior sheathing is exposed to the weather that way. You may need to change the order of construction a bit, but I'd think it would still be doable.
Bill
If you're looking to build in a cold climate, the Alaskan Cold Climate Research Center is a good place to get ideas. They have practical experience building in that climate, so I suspect that their versions of higher performance homes take that into account.
"...formed in 1999 by members of the Alaska State Home Building Association to tackle the challenges of building in cold climates, including remote locations, harsh working conditions, and unstable ground."
Thanks everyone for the quick replies of my silly rant. I have looked at the CCHRC Remote wall which is appealing. The use of foam isn't in my biggest interest with its cost, environmental impact, and a little concern on water being trapped between the layers. The rockwool board looks very tempting but cost is a bit prohibitive.
So yes I've come to double stud being the most effective bang for the buck. Thinking a traditional exterior wall being the load bearing allowing for quick assembly and get the sheeting on before dealing with any insulating. Thinking since we don't have any local contractors and materials are expensive enough to ship in I'm looking at buying a blower and doing the dense fill myself.
You don't have to worry about moisture between layers of rigid foam stacked tightly together. Mositure accumulation is only really a problem when you have an air space or a layer of "fluffy" insulation, such as fiberglass or mineral wool (or cellulose, if you put rigid foam on either side).
Note for dense packing, which is what you want to do with a double stud wall, not all insulation blowers can do it. BE SURE to get a blower that is powerful enough to actually dense pack that wall. If you don't get sufficient density in a double stud wall, you can end up with settling issues that result in air voids forming over time up near the top of the wall. Those voids can cause moisture problems in addition to being big energy losers since they are essentially uninsulated sections of the wall.
Bill
Lstiburek's "ideal double stud wall" is superior from a building science standpoint, but more challenging to build than the typical approach, which though not as ideal in theoretical building science terms, seems to work just fine in the real world as long as the insulation is cellulose or wood fiber treated with borates, and in a cool climate, the wall can dry readily to the exterior. My friend and frequent collaborator Dan Kolbert wrote this about his approach--right after using the same approach on a project I designed: https://www.greenbuildingadvisor.com/article/a-case-for-double-stud-walls. (We do differ on some preferred details, but his track record shows that his system works.)
I framed a wall on the deck conventionally. Then ran 2x4s horizontally 24" OC. At openings turned the 2xs on the flat. Avoided putting the horizontal 2xs at rim joists. Sheathed the wall and stood it up. Now had a 7" cavity. Did 3 to 4" closed cell against the sheathing and the rest with OC. Only thermal bridge is where the 2xs cross.