PTG floor advice

[roach]

I'm about to lay PTG flooring in a timber framed garden office. The base of the building is raised on beam and post contsruction with an 18mm plywood subfloor.

I'm not too bothered about the nails showing but I am going to varnish the floor to give it some protection.

What would you guys recommend as the fixing method and if any underlayment would be required? Do I need to varnish/seal the underneath of the board before laying?

Cheers
roach

 

[ree]

Assuming that you have joists to lay your flooring on, it might be best to drape a membrane over the joists before fixing the T&G straight down - no subfloor require.
Or use a sheet-boarded subfloor over the membrane and joists and pin the T&G to it.
Nail the T&G through the tongue.

With a membrane no undersealing would be necessary.