"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.