Building Regulations and External Wall Insulation

Under Building Regulations, if 25 per cent or more of a wall is to be insulated externally, it is typically necessary to bring the entire wall up to current standards — which makes sense in that, if you’re going to go to the efforts and expense of insulating externally, then you may as well do it well. The thermal performance of the insulated wall must have a U value of no more than 0.30.