Fixing a warm deck down (GRP finish)

[pilsbury]

Going for 18mm T&G OSB3. Thought being it is a little more expensive, but easier to handle (half the width) and will have little waste as I'd have to cut loads off full square edge sheets to fit nicely on the joists. T&G avoids this.

1. What spacing along each joist for base deck screws? 450mm?
2. Once base deck is down, VCL and 120mm insulation laid on top, I lay the top OSB deck. What to use to fix through this lot? Total of near 160mm.... 200mm screws? Or is there special fixings?
3. What spacing for the top deck fixing? 450mm again?
4. Any tips on hitting the joists? Marking up the wall the position, then snap a chalk line?

Cheers

 

[tomfe]

1. fine but remember you are going to fix all the way though again so just walk along the joist and fire every step.
2. long screws are fine but you can also get special fixings, twist nail, thermally broken etc
3. The more the better as GRP can thermally move and make a lot of noise. Glue your T&G.
4. Mark your joists in the ends then snap a chalk line. Check every now and again to make sure they are still hitting.