PIR (polyisocyanurate) insulation boards are a highly effective way to improve energy efficiency in lofts and attics. They are rigid, closed-cell foam panels with excellent thermal performance, helping to reduce heat loss and keep indoor temperatures more stable throughout the year.

PIR boards are commonly used between and under rafters, across loft floors, and on warm roof or ceiling applications (depending on the build-up and ventilation design). When installed correctly with tight joints and appropriate taping/sealing, PIR helps limit air leakage and improves overall comfort.

Unlike flexible quilt insulation, PIR comes as solid boards (often foil-faced) that provide a consistent thickness and reliable insulation value. They are lightweight, easy to cut to size, and widely used in residential construction where space is limited and high insulation performance is required.

What is PIR insulation?

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/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/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.

Are PIR insulation boards a suitable solution for lofts?

PIR (polyisocyanurate) insulation boards are a popular and highly effective option for lofts and attics, especially where you want strong thermal performance without losing too much space. They are rigid foam boards (often foil-faced) that can be cut to size and fitted between rafters or joists, helping to reduce heat loss and improve overall energy efficiency.

PIR boards can also be used to insulate loft floors and sloping ceilings, depending on the roof build-up and ventilation strategy. When installed correctly with tight-fitting joints and appropriate taping/sealing, PIR can help reduce draughts and air leakage, improving comfort and supporting more stable indoor temperatures. Good detailing is key—particularly around joints, edges, and service penetrations—to minimise thermal bridging and reduce the risk of condensation.

In conclusion, PIR insulation boards are a practical, space-efficient and high-performance solution for loft insulation. With correct installation and the right vapour control/ventilation approach for the property, PIR can help homeowners improve comfort and lower heating costs. PIR is often considered a strong modern alternative in loft upgrades, including after spray foam removal, whether used on its own or alongside other insulation types where appropriate.