Thermal Bridging From Screws on a Flat Roof

Hello Steve,

Just came across some of your YouTube videos, brilliant. I bet your company cleans up in London… fair play!

Can I be cheeky and ask a question. I’m doing a small warm roof on my old outside toilet. I want to put a second layer of ply sheet on top of the insulation board, I can screw that down around the edges, but want to put a line of fixings down the middle, but this would mean going through the board until I get to the ply underneath.

Should I do that or put a 4×2 though the middle of the roof? Either way I’m creating thermal bridging, or is there a third way?

Cheers,

James

Good question.

Just screw it down, no 4 x 2 needed. Thermally broken screws are better if you have them, but the loss is no big deal. Look at this blog in which I covered the issue with thermal bridging – click here.

It’s quite possible that internal sweating from around the screws will happen; I’ve never yet had this reported as an issue. The screw you use should be treated in some way and not just mild steel.