Want to cover my very uneven floorboards, couple of questions. what
thickness ply should I use ?, and do I need to pad out the uneveness
with some underlay to stop the ply bouncing, and third - do I need an
expansion gap around the the ply next to the wall ? thanks

wrote:
Want to cover my very uneven floorboards, couple of questions. what
thickness ply should I use ?

1/2" works fine.


and do I need to pad out the uneveness
with some underlay to stop the ply bouncing

That depends on how uneven it is - up to say ~3mm you don't need to do
anything, just screw the ply down well.


and third - do I need an
expansion gap around the the ply next to the wall ? thanks

Ply is pretty dimensionally stable, you don't get much expansion, but I
wouldn't butt the boards hard up against the skirting or wall - leave a
2-3mm gap.


--
Grunff