I’m going to apply 1x purlins over 2″ of polyiso on my existing roof deck in preparation for metal roofing. The roof deck is 1/2″ ply, so I plan to screw through to rafters. I’m looking for some specific recommendations on what type of screw to use, e.g., style, type of point, type of head, sources, etc.
Suggestions?
Replies
robertson (or as they called in the states...square drive) 4 inch #10 zinc deck screws ro
Edited 8/30/2006 1:02 am ET by huddledmass
http://www.screw-products.com/green.htm#blag
4" or longer available, self drilling #17 point, exterior coated wood screws. The cutters on the underside of the head will help prevent splitting the 1x material.
They will also ship directly to your door, instead of having to dick around with having a local dealer order them from their dealer (read: GRK)
Rebuilding my home in Cypress, CA
Also a CRX fanatic!
Basically you want to aim for about 0.75 to 1.25" penetration into the rafter (1.0 to 1.5 if you weren't also going through the sheathing). You're going through 0.75 + 2.0 + 0.5 = 3.25", so a 4" screw will squeek by, though 4.25 would be better. 4.5" would be good in theory, but the extra length causes more screw wobble and makes installation harder, so staying on the short end is preferable.
You should use a weather-resistant screw (ie, galvanized or stainless). It would be wise to put some sort of barrier (eg, strips of rubber membrane) over the screw heads to prevent accidental contact between the screw heads and the metal roofing, possibly causing galvanic damage.