fitting a new internal window ledge

On 13 Apr 2004 14:38:01 -0700, in uk.d-i-y yorks_dales snipped-for-privacy@hotmail.com (the yorkshire dalesman) strung together this:

Gripfill, mortar, wooden wedges, anything really.

Not required.

You are required to use expanding foam to fill around window frames for insulation reasons.

Christian.

If it's well supported, I'd use expanding foam to fill the gaps.

Can't see why.

Although in my experience (limited to a few houses all of early 1900's era) of removing original internal cills (or ledges, whatever..) I've found that they were usually bedded into mortar.

Alex

It's a recent thing. Strangely, the Victorians and Edwardians had neither expanding foam, nor Part L.

Christian.

Funny that! Although I use expanding foam around the edges of the window, I would have thought it was just a little too soft to go under the cill - it is reasonably compressible. In any case, the rest of the wall is quite possibly bricks & mortar, so a little more isn't going to damage any insulation values.

I guess I am just a hater of expanding foam, it's expensive and once you've used what you need it takes forever to clean out the tube so that you may use it more than once.

Alex

Obviously, the expanding foam isn't structural! Provided the sill is well supported by wood or masonry, then the expanding foam should be used to fill any voids. Obviously, if you have an uninsulated solid wall beneath, it won't make much difference. However, with a well insulated cavity or studwork wall, the cold bridging of a thick mortar bed could be quite significant, leading to heat loss and condensation. You don't need to maintain the full u-Value of the wall, but you should reduce the u-Value sufficiently to avoid significant cold patches, which might lead to mould or premature failure of the wood.

Christian.

Thanks Christian, I wasn't aware of the problems of cold bridging (ony ever thought about in rafters & insulation scenario).

Thanks for the well explained reply

Alex

"Christian McArdle" wrote | Obviously, the expanding foam isn't structural!

It isn't? Not even when set? Oh s*it :-)

Owain

I wonder if some nutter (presumably American) has made a house purely from expanding foam, yet? I wonder if some manufacturers would give me 500 cans if I tried?

Christian.

"Christian McArdle" wrote | >> Obviously, the expanding foam isn't structural! | > It isn't? Not even when set? Oh s*it :-) | I wonder if some nutter (presumably American) has made a house | purely from expanding foam, yet? I wonder if some manufacturers | would give me 500 cans if I tried?

It would be cheaper if you got them to give you 500 cans /before/ you tried.

If you could inflate a bouncy castle type structure with a mixture of foam and concrete you could end up with a lightweight, thermally insulated, rapidly-available building.

Owain