CAVITY WALL INSULATION
QBefore agreeing to cavity wall insulation what do I need to know? MIKE, LEEDS Something over 30% of the heat in an uninsulated house escapes through the walls (the actual proportion will vary with the size and shape of the house).that proportion will increase as insulation is added to other parts of the house. An uninsulated cavity wall will have a U value of 1.16W/M2K. Assuming a 50mm cavity, if that is filled with insulation it will reduce the heat lost through the wall to up to a third of its previous level.
COULD IT GO WRONG?
There are plenty of horror stories of cavity wall insulation causing damp penetration to the internal wall most of which are the result of either poor installation or insulation being installed where the cavity is not suitable.there are cases where houses with north or west facing walls, in exposed locations and subject to severe weather conditions suffer with damp problems even when the insulation is properly installed. More generally the problems occur when mortar that fell into the cavity as the wall was being built collects on cavity ties and on the DPC at the bottom of the wall. If those lumps of mortar touch both skins of the wall they act as a bridge for moisture penetration. Cavities are ventilated and that ventilation allows any moisture penetrating to the lumps of mortar to be evaporated away. If the cavity is filled with insulation it is no longer ventilated and penetrating moisture cannot be evaporated away, causing a damp-patch on the inner skin.
A GOOD CAVITY WALL INSULATION COMPANY Will…check
the condition of the cavity before agreeing to install. This is usually done with small inspection cameras. If the cavity is clean then there is no problem with installing insulation. If it is not clean the options are to insulate internally, or externally. In this latter case the cavity must also be filled otherwise heat passing through the inner wall skin will be lost with the ventilation. That external wall insulation will also provide a more waterproof barrier, ensuring no damp penetration to the inner skin.
TIM PULLEN, ENERGY EFFICIENCY EXPERT