In the case of external insulation with a rendered finish, the insulation is mechanically fixed to the outer face of the wall, followed by a breathable membrane and vertically-arranged battens. Stainless steel expanded lathing is then affixed to receive the render, which may be decorated or left with its natural finish.

Appropriate types of insulation include Celotex (www.celotex.co.uk) TB3000 and GA3000, as well as several options from Sto (www.sto.co.uk). The cost of installing such a system would be around £90-£100 per m2 (materials only cost approximately £25-£35 per m2).

External cladding, which works on similar principles to a rendered system, is another option. It’s also mechanically fixed to the external face of a wall, followed by the breather membrane and vertical or horizontal battens of metal or timber. A timber, PVCu or tile finish can then be applied. This is likely to cost around £75-£120 per m2, or £40-£70 per m2 for materials only.

Within each of the above systems you can expect considerable price difference, due to the quality, finish, and materials available. The prices above exclude works to openings, adjustment of doors and windows, roof junctions, flashing and the like. You should also allow for the possible removal and refitting of rainwater and soil pipes.

For internal insulation, laminated insulated plasterboard (70mm thick) is fixed to metal studs with further infill insulation (25mm thick) between the studs. It’s a little cheaper at £40-£60 per m2 installed, or £20-£30 per m2 for materials only.

Peter Judd, www.vbjohnson.co.uk