UTILITIES: insulation

Section L of the building regs (conservation of fuel and power) deals with energy efficiency. You can download all four sections here. Insulation is required at some point in the roof. There are various way that you can do this. You can insulate between the joists (cold loft) or you can insulate under the tiles. So long as it meets the required energy efficiency value building control will be happy.

December 2009: The 60 mm layer of polyisocyanurate thermal insulation is screwed to the rafters.

We elected to use rigid polyisocyanurate thermal insulation (Celotex, EXtratherm etc) for our insulation. To meet the regs we needed to install 135 mm Celotex PIR or similar. There are vaious make of this and they all seem to be about the same price. The sheets come in different thicknesses. I used a layer of 75 mm and a layer of 60 mm to get my depth. It's easy to cut with a saw but makes a lot of mess. It was quite difficult measuring and installing around the ceiling joists because of the rigidity of the sheets. I needed the joists in place to measure but had to take them out to fit the sheets. There was quite a lot of swapping around before I could finally screw the joists to the wall plate.

December 2009: The polyisocyanurate thermal insulation was cut to fit round the joists.I brought the cavity insulation over the wall at top to seal the gap.

December 2009: This Celotex was screwed through to the rafters with 175 mm coach screws. The joins were then taped for an extra seal.