PIR (Polyisocyanurate) Boards.

PIR (polyisocyanurate) insulation boards are a high-performance rigid foam insulation commonly used in UK lofts and attics. They provide excellent thermal efficiency with a relatively slim thickness, making them ideal where headroom is limited or where you want strong insulation without taking up too much space.

PIR boards are typically installed between and/or under rafters, across loft floors, or as part of a warm-roof build-up (depending on the roof design). They are easy to cut to size and, when fitted tightly with joints taped, can improve airtightness and reduce draughts, helping to keep indoor temperatures more stable throughout the year and lower heating demand.

A key benefit of PIR boards is that many are foil-faced, which can help manage moisture movement when installed correctly. Good detailing is essential: boards should be fitted snugly, joints sealed, and the overall roof and loft build-up should follow the correct ventilation and vapour control approach to reduce the risk of condensation.

PIR insulation is widely used in residential construction because it offers consistent performance and a clean finish. However, it’s important to choose the right thickness and installation method for the specific loft and roof structure. For best results, PIR is often combined with the correct vapour control measures and (where needed) additional insulation types for different goals, such as improved acoustic comfort.