What to put under new Steel roof

[srobrien]

Hello all, I hope someone can help. I have ordered a new box profile roof for my garage from a company called planwell. The roof is flat with a slope from front to back.

My plan is to rip of the existing asbestos/concrete curregated panels, lay OSB3 board down on the top of the purlins, felt over the top then screw my steel roof and flashings to the OSB. Then on the inside I will insulate under the OSB with standard glass fibre and install a plasterboard ceiling.

My question is what would you recommend in terms of felting? Should I use a few layers of shed felt glued with bitumen or would a few layers of membrane suffice? If membrane is ok then how should it be fixed to the board.

Here are a few pics of the garage. My aim it to make it draft free and relativly warm.

Thanks

 

[Xenon]

I have a feeling this will sweat. OSB/Membrane(Visquene) rockwool and steel sheet may be better. But i stand to be corrected.

 

[catlad]

You will not need any membrain/felt under your new box section roofing sheets but you may need some extra purlins to catch the osb and new plaster boards as they look a bit wide on the photo.

 

[catlad]

Just seen your location and if you are going to have snow on the roof for months at a time then it might be a good idea to put torch on roofing underlay under the steel sheets.