1. Lay mineral wool insulation between the joists as per manufacturer’s installation guidelines.
2. Lay PIR insulation boards on top of the joists with joints staggered between rows. Ensure all board ends are supported on joists.
3. Where the loft is going to be boarded out it is good practice to mark the line of joists on the surface of the boards.
4. Where the loft is boarded out, the insulation boards will be restrained by the screws used to fix the chipboard, which should have a minimum 30mm penetration into the joists. If the insulation is not being covered then the boards should be fixed by nailing to the joists, with two nails for each board at each joist.
5. When upgrading the insulation in an existing pitched roof, ensure all the pipes and the cold water storage tank are properly insulated to avoid the risks of freezing.
6. Installing insulation over electrical cables will reduce the rate of heat dissipation, which may result in overheating. This is a particular risk with cables to showers and immersion heaters which usually run at a greater proportion of their capacity. Cables may need to be de-rated to prevent overheating. Alternatively, a clear air space may be left between the top of the fibrous insulation and the insulation.
