How do I seal holes in ZIP sheathing from SIP screws?
I’m building a house in Seattle area. Sheathing is airgapped rainscreen o/ 1.5″ polyiso o/ Zip sheathing. My “official” WRB in this stackup is the Zip, although due to the rainscreen and taped polyiso this should be a secondary or tertiary WRB. Still there will be entry paths around openings where caulking or tape workmanship is the onlything keeping water from getting to it.
My question: the polyiso is attached by screwing furring strips through the CI and sheathing into the studs. However this creates thousands of holes in the Zip that I cannot access. Some things I’ve considered:
1) Lay down butyl joist tape over ZIP at the studs so the fasteners self-seal at the WRB. Expensive, laborious, and error-prone.
2) Predrill-n-fill screw holes with caulk. Less expensive and laborious but still a lot of extra work.
3) Do 1 or 2, but only under openingsÂ
4) Don’t worry about it, the water needs to get behind 2 planes to even get to these penetrations and the wall is designed to dry to the interior. The Dude abides.
I’m leaning toward #4 but it does make me second guess why I’m paying extra for Zip instead of CDX if I don’t think it’s that important to have the WRB it provides.
I’m not a contractor so I don’t know how much I should worry about this. Any expert opinions?
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Replies
#4
This is not a boat any water that gets to the joint where the screw enters the Zip will not be under enough pressure to get thru the tight joint between the two.
Walta
Remember also that you need an air barrier on your walls as well as a bulk moisture barrier and the ZIP often serves that purpose too. If doing this, make sure to flash, tape and seal all penetrations in the ZIP prior to installation of the CI. The hundreds of holes for the furring generally have little or no effect on the airtightness of the assembly.
This is a classic case of people on GBA severely overthinking things.
I would go with #4, but I have worked with extremely fastidious, Passive House builders who would run Zip tape at the screwing locations--not so much for initial airtightness, but to help ensure continued airtightness over time as materials move. If you're not going for Passive House or sub-PH airtightness, I wouldn't worry about it.