Fastners on above roof deck insulation….gets crowded?
So I’m continuing to plan our roof detail and started thinking about something which seems strange to me, but possibly I’m over thinking it.
We are planning on this detail from our trusses up
1/2″ ZIP
2″ PolyIso
1″ PolyIso
1″ EPS
1/2″ OSB
Synthetic underlayment
Shingles
So I’ve got two questions in my mind.
1- With the number of nails in each ZIP panel and then the screws in the foam and then 6-1/2″ SIP screws in the OSB….seems like you might be hitting some fasteners on the way in. Is there some sort of technique here that will alleviate this issue? Or is this not really an issue?
2- My ZIP layer will obviously be fully taped and will act as the air control layer of our home. When I go to add the final layer of OSB to sandwich the insulation, I’ll need to drive those screws all the way through that ZIP panel down into the trusses, right? Doesn’t this break the air barrier? Or is this not a concern since it is under a minimum of 3 layers of staggered joints?
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Replies
1. Don't overthink it, but do spend a few minutes thinking about it - I'm sure it's not too hard to come up with a screw staggering logic.
2. If you can target (and hit) the trusses you'll be fine. If you miss the truss, leave the screw in.
I have a similar but not exact situation where I'll have about 15" of rigid foam to screw through, and for the 1st 7.5" I'll be using strapping and long timber frame screws into my rafters. For the 2nd layer of 7.5" I'll be screwing down through the sheathing into the strapping
The screws through the foam are just to hold the foam in place temporarily until that outer layer of OSB holds everything together. Don't need more than a few screws for the foam, and they can go right through the field of the ZIP if you want (instead of into a truss chord), as there is not really any need to make a structural connection into a truss with a non-structural material.
Why are you screwing the foam and the OSB? As long as the outside OSB is fastened, the foam will stay in place. Also, I might consider ZIP in the outer layer, but I guess it depends how much you trust your underlayment.