Vapour barriers?

[Vernon]

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?

thanks

Vernon

[Grimly Curmudgeon]

We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember "Vernon" saying something like:

It goes on the moist side of the insulation - the inner side. If you put it on the outer side, the moisture vapour will permeate the insulation and condense within it, causing rot of timbers and other nasties.

[Cod Roe]

You might find this a good solution, phenolic foam (Celotex equivalent) , plasterboard and vapour barrier all in one:

has worked wonders on the solid walls in my Victorian solid wall house. I would either dot and dab or battens with a small cavity, British Gypsum have clear instruction on their site.

[Vernon]

> It has worked wonders on the solid walls in my Victorian solid wall house.

Sounds interesting, I expect it is expensive, and where to buy? Not seen it in local builders merchants?

[The Natural Philosopher]

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.

[Colin Wilson]

...just wondering if all this stuff is in the wiki - if not, it would be a useful category to have...