On Dec 21, 6:07*am, Mike Tomlinson wrote:
In article
s.com, Jim writes

That is to say, fix all the floorboards, then lay celotex/kingspan
(I'll have to look those up), then foil tape on top of that, and then
let the fitters lay underlay and carpet ontop of that?

Celotex is a foil-backed insulation mat, about an inch thick. *

For the OP's situtaion it will need to be about 100mm thick to meet
building regs. The required thickness depends on the (exposed
perimiter)/area of the floor. take a look he
http://www.insulation.kingspan.com/uk/pdf/tf73.pdf to see how thick it
needs to be.

Fllorboard gap filler we used was called "gapseal" and it worked
well.

Robert