OSB3 for Flat Roof - T&G or normal

22 Jun 2009
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United Kingdom
Just have a flat roof built and a pretty simple question to answer (I hope).

Construction to be (starting from the top):

Sarnafil membrane
18mm OSB3 board
120mm foil backed insulation
1200g polythene VCL
18mm OSB3 board deck
Easi-Joists (600mm c/c)

The 18mm deck (sat on the firrings), I'm going to use standard OSB3 board.

However, the OSB3 on top of the insulation, can I use standard board or does it need to be the T&G type?

If it needs to be T&G, can the boards be 2440x1220 or do they need to be the 2440 x 600 size?

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I don't use anything else nowadays but T&G OSB and as far as I know it only comes in one size.

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