Sealing Sheathing to Foundation (zip -to- icf)
This is a continuation of some of the thoughts in the comments on this post from a couple years ago: https://www.greenbuildingadvisor.com/question/air-seal-sheathing-to-foundation
I’ve got zip sheathing coming down to an ICF foundation. I’ve got a ~1/2″ gap from sheathing to foundation. If I was to use liquid flash to air seal but also to give a continuous plan for water to run off (the zip will have a rain screen and then siding). Could I fill my gap between zip and icf with spray foam to make an easier (continuous) surface for tape or liquid flash. Or is this a terrible idea and will cause the zip to potentially hold moisture? Maybe this is a better place metal flashing (although I would like to better air seal the sheathing to framing connection)?
I have attached two photos showing the gap. I am planning on cutting all the ICF at a 45deg angle.
Thanks!
-Cedar
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This is a situation where I like to use Siga Fentrim tape. It's super sticky and vapor permeable so it won't hold water back, as long as it's not a lot of water. It sticks well to the face of Zip sheathing and to foam. Other brands such as Pro Clima have similar tapes. If it will be exposed, I would run metal flashing over the surface of the tape and tape the flashing to the wall as well.
With either of those details, you shouldn't need to add spray foam, but I don't think it would hurt anything if you did.
Fantastic. Thanks for this. That looks a great tape for this use. With concrete there I wanted something that was vapor permeable.
I was thinking about something like zip liquid flash, but honestly wasn't sure if it can be used on ICF foam (EPS).
I'm pretty sure Zip Liquid Flash is compatible with EPS but I don't have enough experience with it to say. Huber's technical resources would probably have that information, or their technical support department certainly would. But Fentrim is my go-to for this kind of situation, and I know many high-performance builders who would agree.
I recently added on to my house with ICF and flushed the 2" Zip-R with the foundation insulation. First I sealed my sill plates to the sheet waterproofing with 9" zip tape for plenty of coverage. I left a 1/2" gap at the bottom of panel, spray foamed the gap and then taped the seam between ICF and Zip. Here are a few photos
Thanks for those pictures and details. Not to get too far off topic but what's that drain mat/dimple board product?
That is normally a commercial product, but in my case it provided protection for the sheet waterproofing. Also helps get all the water down to the footing drain
In an ICF system, the concrete is the air barrier, not the foam. If you have any way to seal back to the concrete core, it will provide a tighter air barrier, if your zip is your primary air barrier.
That's a good point. What about running the waterproof barrier/membrane for the ICF up to the sill plate and protecting the membrane from UV?
That said I did also run two thick beads of Contega HF adhesive under my mud-sill. Would taping or liquid flash from the zip sheathing to the mud-sill be enough to make that air barrier tie into the concrete?
What are you using for your water barrier on the ICF? Colophene, Resisto,, ProtectoWrap? The fully adhered membrane should go up to the sill plate.
I'm planning on using the Nudura peel&stick product along with the nudura primer. Every piece of documentation I can find says to stop the water barrier at the soil/grade line. But I really wan to to run it up to the sill plate as you suggest. Then I could use the Fentrim to seal from zip sheathing to the waterproof membrane.
Why does everything say to stop the waterproof membrane at the soil line? I understand that it can't be exposed to UV, I was planning on covering it with an opaque dimple/drain mat for UV protection. Is there another reason its a bad idea to run the waterproof membrane to the sill plate?
You could also use 1/2 inch PVC fascia trim to cover/protect the exterior foam. See Building Science Insights 020. That has cellular PVC protection board for the exterior foam.
That looks like a great solution. I'll see what I can source around here. Thanks
There is another product that looks kind of like FRP almost to protect the ICF above grade. Its called Nudo Groundbreaker
https://www.menards.com/main/building-materials/insulation/foundation-insulation-coatings/nudo-50-groundbreaker-trade-foundation-insulation-barrier/1599620/p-1444449841250-c-9532.htm