On Oct 11, 12:47=A0am, "js.b1" wrote: ////
That maybe right heat-wise but what is being forgotten is that the cavity wall is itself a vertical damp proof course. You bridge it at your peril. Most outer leaf building material (& mortar courses) is slightly porous and in a bare cavity what H2O that seeps through should run down the inside of the outer leaf & out at the drain holes just below the horizontal wall dpc.
You need to be absolutely certain that the filling (1) does not allow moisture to cross the gap (2) does not deteriorate in the presence of moisture (eg try damping rockwool/glass fibre). Only a small amount of moisture is involved. Deleterious effects (such as shaling of brickwork) take a long time to show up. Consequently you are looking for guarantees that will be valid 10-20 years out: who will honour the guarantee in 15 years?. Performance varies between filling materials, but IMHO beware of blown materials which are rockwool-type based.
Ideally there should be a 25mm (1 inch) air gap in the cavity against the outer leaf.
HTH