Very creaky floorboards in new extension

trogg

As leveller2911 said above.
I've done it myself, screwed the flooring into the joists without drilling a hole into the flooring first.

beaker141

I did my own loft flooring (full b regs conversion) and it doesnt creak at all - whereas the extension the builder did - creaks a lot!

In the loft between the chipboard floor and joists, I put the black dpc membrane strip between the joist and boards (tip from my electrician), made sure all T&G joints were on a joist (it helped that they were 3" thick) or took the T&G off and had butt joints, drilled pilot hole for the screws and then screwed them down whilst stood on the board to keep it in contact with the joist.

The builder however, left the T&G joints wherever they occured (which is probably normal), didnt use pilot holes, missed the joists with some screws, didnt use glue and didnt use any DPC (again normal not to).