screwing down plywood ends over ridged foam
Ogden2024
| Posted in Green Building Techniques on
On my planned roof I will have 4 inches of polyiso with plywood on top.I have read some comments on how hard it can be to hit the rafters. It seems the hardest part will be the panel ends and the flat screw heads not being flat if I angel the screw. The roof will be open from the bottom to see shiners .
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Replies
Ogden2024,
Buy yourself a portable drill press, which will help keep the screws straight. For those you need to angle slightly, put a small shim under one side. With 4" of foam, the angle of the screw head will be so slight it won't be a problem.
Malcolms solution is elegant, but you can also make a simple jig the way I've described here in the past, but cutting a slot into some scrap framing lumber and using it as a guide for the long screws.
Another option is to put in some strategically placed furring so that you don't have to get all the way through the foam in every location you want a fastener.
Bill
Thanks for the tips I had a portable drill press along time ago it was handy for lots of things.
Ogden2024,
They are great for aligning bolts though timbers too.
If you look at the install manual of nailbase panels ie:
https://hunterpanels.com/wp-content/uploads/2023/06/UPDATED-H-Shield-NB-Installation-Guide-Web-File-Version-7.7.23.pdf
The screws simply go into the deck bellow. There is no need to hit rafters. It is slightly stronger if you do hit the rafters, but not something you need to watch. The screw tips are a small thermal bridge so you can aim to hit rafters, but if you miss them, I wouldn't loose much sleep.
Make sure to protect the insulation at the edges of the roof to keep critters out. Best is to rip 2x lumber to the thickness of the foam around all sides and nail the 2nd roof deck to that.
He mentioned the screws would show
What is the roof deck material, plywood?
While it is a PITA, marking the rafter locations on the roof deck and snapping a line after the I&W and underlayment are installed is not that bad a strategy