Suggested Materials for Warm Deck Flat Roof

7 Oct 2018
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United Kingdom
Hi all

Our single storey extension walls are up and we're looking to buy the materials for the flat roof and I thought I'd ask for some advice. Just for info, it's a house we are selling on and the roof is 8m x 6m Inc short overhang/canopy.

We're installing a lantern so as per our structural calcs, it needs to be 9x2 joists where the long trimmers are 3 joists bolted together and doubles on the short trimmers. Would any here pay double the price for posi/open web joists? I'm thinking of installation time and fit out of services after?

We're going for a warm deck so on top of the joists, I was going for 18mm osb 3 T&G, then I believe we need a vapour barrier, then 120mm rigid, foil backed insulation and a top layer of 18mm osb 3 T&G with the waterproof covering to be EPDM.

Anyone have suggestions for the vapour barrier as there seems to be loads at varying prices? Does it need to be self adhesive?

Any opinions on the insulation itself and where to buy from? Any particular brands that are good value whilst still being efficient?

Does the osb 3 T&G need to be glued when fitted?
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