On Mon, 10 Aug 2009 01:31:13 GMT, "BigWallop"
wrote:

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.


What you said makes perfect sense but if the cavity is filled, then
there will be no chimney effect.

The cavity of the walls is filled with some sort of white substance.
It is like a lump of foam but it crumbles on touch. I think they
drilled holes into the breeze blocks and filled the cavity through
those, hence this section in front of the door was never done. I agree
it could become a bridge for damp so was considering polystyrene and
some DPM.