tinning a roof

[baler 46]

Hi

Just wondering, I'm put tin on my roof and im putting purlins on right now, and i wondering if my screws are long Enif to hold down the purlins?The screw length is 3 1/8 inches long that I'm using to go through a 1by4 then 1 layer of asphalt shingles then a layer of wood shingles then tongue and grove underlayment a 3/4 inch thick then rafters. Do you think i need longer screws to screw down the purlins, maybe 4 inch constructions screws I only go into that rafter about a 1/4 inch.The screws to use in the tin are 2 1/2 inches long. Any ideas

 

[Anonymous-0]

use longer screws for piece of mind. I would want them into the wood one inch. On some new commercial roofs, with the panels with plywood on each side and four inch foam in the center the screws are long, so they are available. Just need a good screw gun.