"Man at B&Q" wrote in message
...
On Aug 10, 2:31 am, "BigWallop"
wrote:
"Fred" wrote in message

...

On Sat, 08 Aug 2009 10:57:33 +0100 (BST), "Dave Liquorice"
wrote:

I'd remove the rubble, there is small risk that it could form a damp
bridge. If you have some suitable insulation put it in the gap. Think
about damp proof courses and not bridging the cavity when you
concrete over.

That's what I was thinking, thanks for confirming that. I don't have
anything suitable to hand, so what do you suggest: a small sheet of
polystyrene from Wickes? Thanks again.

It is always best to keep the gap clear of any debris, rubble, muck, brick
bits, everything else. The cavity is there to stop damp coming through the
walls and to keep an air gap for the walls to breath and sweat any
moisture
away.

Damp comes from both inside and outside, so the cavity helps to keep both
skins of the wall dry by allowing air to travel through from the outside
air
bricks and any inside vents. It should have a natural chimney effect to
the
eaves of the roof space (warmer air rises naturally, hence the chimney
effect). So best to keep the cavity as clear and clean as you possibly
can.

So you wouldn't recommend cavity wall insulation, then?

MBQ

In some cases. No, I wouldn't. It is possible to create more problems with
indoor condensation and outside retention of water, if the job of filling
the cavity is not done properly. A true cavity wall expert is also looking
at the ventilation from inside and outside the property. If there is no
adequate ventilation, things like cooking, washing and even breathing would
build up loads of moisture into the air inside the building. Blocking the
air flow through the cavity may actually stop a lot of the moisture from
escaping through the inner skin ventilation of the walls. In such
circumstances, extra ventilation, properly installed, may have to be advised
along with the insulation works.

So don't go thinking that the cavity isn't there for a worthy cause. It
wouldn't be designed into a building if it wasn't actually doing something
purposeful. Who wants to pay for a second skin of brick or block if one
skin would be enough. It is there for an important purpose and should be
treated as an important part of the whole structure of the build. Don't
think it can just be filled with any old water resistant material and Bobs
your proverbial Uncle. Cavity wall insulation is also designed to allow air
to flow past it or through it, all be it a much slower flow of air, but it
still allows a flow of air through the cavity. If it was hard packed, it
would create a worse bridge between skins and cause rot and damp to run rife
through the whole house.

So. No. I wouldn't advise cavity wall insulation in all cases. I would
also advise that if you would like such works to be done on your property,
that it be done by properly trained persons, with the proper materials and
equipment.