In general the insulation is done internally if it is retrofitted, or within the brick courses if it is a new build. The main products for retrofitting insulation on walls are made by the three biggest suppliers Kingspan, Celotex and British Gypsum. These boards come in two varieties, those backed with plasterboard and those not. These are foil backed on both sides and are by far and away the most popular selling. Celotex GA4000 range and Kingspan Tp10 range make these boards and they are to all intents indistinguishable from a thermal performance perspective. The new regulations have meant that greater and greater thickness are now required to achieve the required U value. For walls this is likely to be in the region of 70mm of insulation but this is very much dependent on the wall construction (i.e. brick or block cavity or non cavity).
