Wall Cavity Insulation and Zip R3 Sheathing
Seeking ideas for insulating wall cavities with Zip R3 sheathing
Hi,
We live in climate zone 5a.
We had planned to use Zip R9 sheathing on the exterior walls (2×4’s) with R-15 Rockwool batts and a class III vapor retarder (Paint) – however, the contractor chose Zip R3 on the gable walls unbeknownst to us until recently
Because the interior drywall has not yet been put up, I am looking for options for the wall cavity insulation that will prevent condensation, mold growth and allow water vapor to escape if needed.
One of the gable walls has numerous electrical wires in it attached to the circuit breaker box and a 1 cm diameter gas pipe running through it; and the other has 3 large windows encompassing ~ 70 of the wall.
Although spray foam is likely a good option, I have concerns regarding off-gassing if not done properly and am not willing to risk this due to a family member’s health issues.
One insulation contractor recommended cutting and placing foam board insulation in the wall cavities and air sealing around the periphery of the boards with canned spray foam to prevent vapor diffusion into the wall cavity from the home. He is thinking of using the foil-faced polyisocyanurate. He also thinks this would be easier than placing Rockwool batts and an Intello vapor retarder due to the makeup of the wall cavities (wires, pipes, windows).
Short of taking the siding down and adding additional continuous exterior insulation, or using non-canned spray foam, does anyone have any practical ideas?
Thank you.
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Replies
This is closest I can quickly find:
http://effectiver.ca/calculator/wall.php?id=4329
This seems to work well in all climates so, condensation is not much of an issue. The thin layer of foam on the ZipR does offer some permeability so the walls can dry to the outside. The smart vapor retarder or faced batts are needed though. For reference Edmonton is Zone 7, Toronto Zone 5 and Montreal Zone 6.
I don't think a cut and cobble would work better but would certainly be way more work to build. Interior vapor retarder is a simple install, even when detailed properly it is at best about an afternoon for an entire building face assuming simple geometry.
I agree with you on skipping spray foam, this is the last thing you want in a new build.
Hi Akos,
Thank you for the information.
Regarding faced batts- the only option would be fiberglass, correct?
With our set up of Zip R on the exterior - with a rainscreen,
do you think the cut and cobble/seal approach using foil faced polyisocyanate would be contraindicated due to potential moisture build up in the wall cavity (no place for moisture to escape...) - or if it is well sealed with canned spray foam within the wall cavity could I expect it to keep water vapor from the home out?
Faced MW does exist but it is hard to find. Generally your best bet is to go with unfaced high density batts (mineral wool or fiberglass, both work well) and use a smart vapor retarder such as Membrain or Intello plus.
Regular R12/R13 faced fiberglass batts will work just as well, it won't change your assembly R value all that much by using it in this one area.
Too many low perm layers can sometimes get you into trouble. My gut feeling is the cut and cobble will work well but the batt+vapor retarder is the more robust option. With cut and cobble the center cavity R value seems more impressive but because of the thermal bridging of the studs, the overall assembly R value doesn't change all that much.
This makes sense, Akos, I like the idea of mineral wool with Intello plus. Thank you for your suggestions.
What is your adopted code?
Unless the wall is rather thick, R-3 continuous insulation is not going to help you meet code in zone 5.
> We had planned to use Zip R9 sheathing on the exterior walls (2×4’s) with R-15 Rockwool batts and a class III vapor retarder (Paint) – however, the contractor chose Zip R3 on the gable walls unbeknownst to us until recently
I don't quite understand this. What is on the drawings?
Hi Patrick,
I would have to write a novel to explain the remodeling disaster we went through last year with a 'reputable' contractor that resulted in my question on this forum (still in the process of re-doing things that were not done per plan).
In any event, you are right-- R 3 is not enough for exterior continuous insulation in Zone 5 to achieve code - that's why R9 was chosen. Now I am just looking for the best solution that would not involve taking off the siding and adding more exterior insulation, while also minimizing the risk of condensation in the wall cavity due to suboptimal exterior/interior insulation ratios.
You might also consider the bonfig wall.
https://www.finehomebuilding.com/project-guides/insulation/breaking-the-thermal-bridge
You would lose a little interior space but you would most likely not notice unless things are really tight.
Thank you for informing me of this technique - I had not heard of it before. I will discuss this and Akos' suggestions with my contractor/insulator. I am relieved to know there are options.