I couldn't get any OSB3 tongue and groove deck so i'm using the 8x4 OSB3 decking which is fine but I want to know what expansion gap I need to allow for?

You will need to allow a 3mm gap between all the edges of the OSB deck to allow for thermal expansion and contraction. Where the decking comes into contact with a wall allow a gap of 25mm.

If you have any more questions, check out our decking guide or speak with one of our technical team before you get started.