Carpet tiles over old floorboards

[absolute0]

I'm looking to replace our carpet in our makeshift home office with carpet tiles, however, the floorboards are old, warped and uneven.

If I ply line the floor do I need to leave an expansion gap around the skirting? If so, what's the recommended gap?

Also what size ply would people recommend?

Thanks

 

[footprints]

I normally use hardboard (stapled or pinned to the floor) works just fine, very little movement unlike timber.
I also lay paper felt or lining paper under the hardboard, although newspaper is fine.
For carpet lay rough side up for tiles that use D/S tape lay shiny side up.

 

[crazydaze]

6mm ply and leave a couple of mm round each board so they don't squeak together.

4mm Hardboard 'should' be ok but with wheeled chairs etc Ply would be that bit stronger.