Simple wall assembly feedback
Tor89
| Posted in Energy Efficiency and Durability on
I live in Zone 5A. I’m exploring the world of exterior insulation and wanted to get some feedback on my proposed assembly.
Interior
1/2 Drywall
2×6 w/Fiberglass Batts (Faced) – R-19
Zip Sheathing
1.5″ Rigid Insulation – R7.5 (Untaped)
Vinyl Siding
Exterior
I’ve read articles that say you should have ~33% of your insulation be exterior and this is slightly under but looking at IRC Tables R702.7(1) & R702.7(3) as well as N1102.1.3 this assembly meets all of them. Should I be worried about moisture in the walls with this assembly? Any changes that should be considered?
I could increase to 2″ of insulation but I’m concerned about fastening the vinyl through two inches. I feel comfortable going through 1.5″ but am not as sure about going through 2″. I did check with a vinyl company that a local supply house has and verified that as long as the fastener penetrates 1.25″ through the sheathing/stud that strapping isn’t needed and meets their warranty requirements. This means with the above assembly I could use 3″ fasteners.
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Replies
Tor89,
It looks likes good, and as you say, fairly simple. One of the nice things about 1 1/2" deep foam is you can use common 2"x stock for blocking or bucks.
https://www.greenbuildingadvisor.com/article/calculating-the-minimum-thickness-of-rigid-foam-sheathing
Yes, I found a video from Matt Risinger that I believe I will follow for the bucks that attaches 2x's to the face of the wall.
I am trying to locate the correct detail to use for the base of the wall though. I was thinking of using the same detail as the window buck. Attach pressure treated 2x to the face of the wall base with drip cap over it. This would give the bottom of the foam protection and give the siding starter strip something solid to be attached to ensuring a nice level start. Any thoughts on this?
I was also thinking of maybe taping the bottom of the foam to discourage insects too? Since it is vinyl I'm sure they could get to the foam by other means but this area seems like it would be the most obvious location they would be able to penetrate the foam.
Tor89,
Rather than a drip-flashing, I would cover that base pt 2"x2" with a piece of Zip tape. The flashing would have to be sloped, exposing the bottom of the foam, and would need taping to the Zip anyway.
Thanks. As I’ve not used Zip before I wasn’t sure if it is best practice to use both tape and flashing or just the tape. Do you think the same detail could be used for the top of the window bucks or, since this is a more sensitive area both the tape and flashing would be best?
Tor89,
Above openings I would use metal head-flashing with end dams. I'd be surprised if any moisture made its way to that base piece of 2"x. Tape there is fine.