Vernon wrote:
Can someone be kind enough to explain how and where these go please.

We have a small utility room behind the garage, single brick
construction, inner walls are tiled, always cold inside. There is a
radiator, and it will heat the place up, but it doesn't take long to
cool down again. So I am looking at removing tiles and drylining walls.
I know the flatroof has rockwool insulation, as we had the roof replaced
last year, but maybe look to pull ceiling down and put celotex between
joists instead of rockwool. Then either put battons on wall, celotex
then plasterboard, creating an air gap where the battons are, or
skipping the battons and attaching celotex directly to wall.

So where does the vapour barrier go, some say it would go behind
insulation, some say infront, I don't really understand what it is for?


It goes on the warm side of the insulation to keep foetid air in the
warm, so it doesn;t condense.

The other place for a breathable membrane is where you want a
showerproof OUTSIDE but can't guarantee that water wont get behind it:
In this cases it keeps the rain off, but lets the damp percolate out.


In your case, simply use foil backed board after insulating.

Or if its Celotex, its foiled anyway, simply tape over the celotex and
the joists with foil tape.

thanks

Vernon