Opinions on a wall system
Hello. I would appreciate any thoughtful opinions on a wall system I am looking into.
I’m planning a build in Calgary, Alberta. I was originally thinking of a Larsen Truss-type wall but now am leaning towards pre-manufactured panels for a number of reasons. Other than SIPs, I have come across a company that provides a custom wall design in 6, 8, or 10 inch depths that they claim limits thermal bridging and provides superior moisture control. I visited their facility last week and was really impressed. It’s not exactly how I would build a wall, but with it, I don’t have to build the wall. My time and other labour costs are important.
It is Pacific Homes’ “smartwall”. Here’s a link:
http://pacific-homes.com/pacific-smartwall-how-it-works/
The 10″ wall is claimed to have an overall R-value of 36. What do you think?
Thank you.
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Replies
The r-value seems a little optimistic. Is the field-applied EPS installed between the purlins instead of covering the 10 inch studs?
The "eliminates dew point" language is interesting.
If the wall works for you, that's great. Here are some of my thoughts...
1. I agree that it seems either disingenuous or indicative of naivete to state that the dewpoint is eliminated.
2. I have found that prebuilt walls often seem like a great idea, but then you factor in freight and crane costs and you'll find the cost starts to seem less advantageous. Remember, you are still paying labor costs, just elsewhere.
3. If you are building with prefab walls, you need to be absolutely sure your design is dialed in before ordering.
4. Often the wall itself looks good but the weakness comes at wall joins i have not looked at the wall join detail, but you should examine it.
5. I, personally, am concerned about combustible stick built walls filled with combustible foam. This may not be of concern to you, but it will also be of concern to the firefighters who visit your home in the event of a fire.
6. One great advantage of prefab walls can be scheduling, as the walls are built while the slab is being poured.
If you want to add to your list of companies that make high-R wall panel that are not traditional SIPS, take a look at Ecocor, http://ecocor.us
The claimed R36 R-value is pretty much center-cavity R base on the performance of Type-I EPS at a mean temp through the foam of 40F, not "whole-wall-R" or 1/U-factor. There is 7.75" of factory applied foam, plus 1" of site applied foam for a total of 8.75" of EPS. R36/8.75" = R4.12, which is about the 40F mean temp performance of Type-I EPS, and somewhat lower then the 75F performance of Type-II EPS.
Only 1/2" of EPS (~R2) as the thermal break over much of the 7.25" thick/R8.5-R9 framing fraction isn't much of a thermal break, then they go and screw it up by mounting the 2x8 framing on a solid 2x10 thermally bridging bottom & doubled top plates, so the pathetic 1/2" thermal break isn't even over the entire framing fraction.
If interior air ever leaks around the EPS to the 1/2" fir sheathing can collect quite a bit of moisture over a winter, and with 8.75" of Type-I EPS between the sheathing and the interior it's ability to dry toward the interior is impeded as well, at about 0.6 perms, but it's no worse than air leaks in a gypsum wallboard painted with "vapor barrier latex" primer. I suspect they mitigate the air leakage that by using the fully framed sheathing wall as the mold, expanding the EPS into it so that it's very air tight, then applying the interior side furring after the fact.
A Larsen Truss or double-studwall of equal wall thickness (10.5" from the exterior of the fir sheathing to the interior paint on 1/2" gyprock, 9.5" if only counting the framing depth) can beat the whole-wall performance of the R36 Smartwall by quite a bit without using any foam insulation simply by providing a more credible thermal break. A structural 2x4 exterior set of studs, with a non-structural 2x3 (finger jointed studs for better wall-flatness) would have 3.5" of room for thermal break between the sets of studs & plates. With 9.5" of cellulose cavity fill the center-cavity R would be R35, but with R13 of thermal break the R value of the ~25% framing fraction would be roughly double that of the R36 Smartwall, for a considerably lower U-factor.