Wall Plan Review
chris_the_new_guy
| Posted in General Questions on
Hello everyone, my name is Chris and I’m starting a new build just outside of Toronto, Canada. I’m pretty much in the same climate zone as Detroit.
My house will be a poured basement foundation, with 2 stories approx 4000 sq feet climate controlled. I’d like to create an air tight assembly that is very energy efficient. I would like to clad the walls in thin stone veneer, and so decided the zip R would be my best bet, rather than exterior Mineral wool. I know there is some vapour issues with zip R in northern climates, but does anyone see any major issues with the assembly I’ve put together here?
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Replies
Closed cell spray foam on the inside is likely a waste of money: https://www.greenbuildingadvisor.com/article/installing-closed-cell-spray-foam-between-studs-is-a-waste
Simplify things and just do a full thickness batt, dense pack cellulose, or open cell spray foam.
> I would like to clad the walls in thin stone veneer, and so decided the zip R would be my best bet, rather than exterior Mineral wool.
You may want/need an additional WRB over the Zip R-sheathing, then: https://www.huberwood.com/uploads/documents/technical/documents/Housewrap-over-ZIP-System-Sheathing-Tech-Tip-Wall-ZIP-System.pdf
Another comment: Not sure if "water resistant tar" is technically damp proofing or water proofing, but you want a water proofing product.
Thanks for your reply Patrick. I was thinking the closed cell foam would be a nice product because it would also provide an air and vapour barrier. I also wanted to get as close to an R-40 as possible and to make sure that the foam surface of zip R was not a condensing plane. I imagine as long as some type of insulation is in there it wouldn’t be though. As far as the thermal bridging of the studs goes, wouldn’t the zip R foam prevent or reduce the thermal bridging of the studs seeing that the studs would not be in contact with the cold surface? If I went with open Cell in the 5.5 inch cavity I could get to R 20 or so but with the closed cell flash and bat I get to R 28
As far as adhering the stone veneer I was thinking of using Dorkens dry and lath dimple May product as a rain screen between the stone and the zip osb.
Let me know what you think.
The water resistant tar isn’t technically waterproofing but I figured with 2 inches of closed cell spray foam on the interior of the foundation walls creating a monolithic water proof layer the exterior waterproofing wasn’t as important.
> I was thinking the closed cell foam would be a nice product because it would also provide an air and vapour barrier.
Wouldn't the Zip R be your air barrier?
> If I went with open Cell in the 5.5 inch cavity I could get to R 20 or so but with the closed cell flash and bat I get to R 28
You need to be thinking in terms of whole wall R value, not cavity R value. Depending on framing details (i.e. how much wood is in the wall), my quick math estimates the whole wall R value differences somewhere around R-23 vs R-20.
Check out BEopt. You can model these as different options and you may be shocked to see how little this affects your heating/cooling load and energy expenditures.
Chris,
Your wall will have no issues from a water-vapor perspective as the CC spray foam will serve as a class 1 vapor retarder. Also, combined with the exterior-ish foam within the Zip R panel, the interior surface of the spray foam will remain above dew point in your climate. I assume you are going to use the stone veneer that has an air gap behind it?
This wall has been used (invented?) by Steve Baczek, a highly regarded architect for high performance homes. .
By the way, what program did you use to draft this detail?
Lol, hi Rick. I’m familiar with Steve Baczek from YouTube. I got this wall diagram from a screen shot of Matt Risingers YouTube channel. It originally had plywood, delta vent sa, and mineral wool, but I used my Apple preview paint skills and made the modifications I wanted.
2.5" ZipR is hard to work with as you need special nail gun+nails. I would step this down to R9 panels, much easier. If you want some extra R value, bump up your studs to 2x8.
As others have said the SPF in the stud bay is a waste of money. You'll need to tape the ZIP anyways to seal it, might as well use it as your air barrier. You can install a smart vapor retarder behind the drywall instead of poly to add additional drying capacity.
Adhered stone veneer is generally a troublesome product, something that is too easy to install badly, I would stay away from it. Standard vaneer install with ties is fine, make sure to keep the required gap behind.
I saw warm board in your sketch. In low load houses, floor heat doesn't do as much as you think. Because of the low load, it never gets warm enough to get the warm toes feel you are thinking about. A properly designed and sized ducted HVAC system works great for much less money plus you'll need that anyways for AC, might as well use it also for heat. Spend a bit of your warmboard+hydronics money instead on getting and HVAC engineer to size your setup and a modulating heat pump system.
What R value in walls works best with radiant floor heat to keep the toes nice and toasty? I realize it all depends on outside temperature, water temp etc...
As a ball park number, would R 30 in walls be too much?
R30 would be too much. Code minimum would be too much.
Yup, code min is too much. Around me in Zone5, works great in old double brick houses, so around R5 walls.
The way to get around this in low load homes is to only heat areas where you'll be walking. This is much cheaper as you'll need much less piping and floor boards/heat plates. You'll have to do a bit of math to figure out the area that should be heated. Something between 1/3 to 1/2 of the total floor area.
Even if you are doing the above, it will be way cheaper to do the bulk heating with a heat pump and have electric resistance floor heat in these areas. Since it is not providing the whole heat for the space, the operating cost of the electric resistance heat will be pretty small. Small enough that there is no realistic ROI by going to hydronic.
Thanks for all of the great info. I’ve made some adjustments (ie going with open cell in the cavity bay and the 2 inch Zip R). This should satisfy all of the previous wall concerns. Does the zip to foundation transition work ok by using a 2x8 mud sill and resting the 2 inch zip on it to create no overhang behind the brick ledge?
I’m going to look into the specific electric floor heating and heat pump. Don’t want to waste my hard earned money if I can achieve the same results for less expense.