How and where to use guide
Rigid PIR Insulation 1200 x 2400 x 75mm
Typical applications
These 75mm PIR boards are commonly used in cavity wall insulation, above-rafter roof insulation, timber floor upgrades and internal wall lining in retrofit projects. The 175 kPa compressive strength makes them suitable for floors where they can be laid directly onto concrete or timber joists, and for walls where they sit between studs or battens. In roof applications, boards are typically laid between rafters or above the rafter line depending on your design strategy. The foil facing acts as a vapour control layer, reducing the need for separate membranes in many configurations.
- Cavity wall insulation: fit between masonry leaves with appropriate cavity ties and support
- Pitched roofs: install between or above rafters, ensuring adequate ventilation where required
- Timber floors: lay on joists or concrete with appropriate support and edge restraint
- Internal wall lining: fix to existing walls using adhesive or mechanical fixings
- Flat roofs: install as part of warm roof or inverted roof systems with appropriate covering
Installation and fixing
PIR boards are lightweight and straightforward to handle on site. The standard 1200 x 2400mm format fits most structural spacings with minimal cutting. Boards can be fixed using foam-compatible adhesives, mechanical fixings such as insulation pins or battens, or a combination depending on application. Always ensure boards are cut square and fitted tightly to minimise thermal bridging at joints. The foil facing should be left intact where it serves as vapour control; if you must cut or damage the facing, seal the exposed foam edge with appropriate tape or sealant. Stagger board joints to avoid continuous weak lines through the insulation layer.
- Cut boards with a fine-toothed saw or hot-wire cutter to minimise dust and maintain clean edges
- Use foam-compatible adhesives or mechanical fixings appropriate to your substrate
- Fit boards tightly to minimise gaps; seal any unavoidable joints with foam-compatible tape
- Protect foil facing during installation to maintain vapour control integrity
- Stagger joints in successive layers to break thermal bridges
Limitations and site management
PIR foam is combustible and must be protected with appropriate fire-rated coverings in accordance with Building Regulations. Do not expose boards to direct sunlight or UV light for extended periods as this degrades the foam and facing. Protect boards from moisture during storage and installation; keep them dry and covered on site. The 75mm thickness is a fixed dimension, so ensure your design accommodates this rather than attempting to compress or thin the boards. Boards should not be used in applications where they will be subject to sustained high temperatures or direct contact with certain solvents.
- Provide fire-rated covering or lining as required by Building Regulations
- Store boards undercover and keep dry until installation
- Do not expose to prolonged direct sunlight or UV
- Do not compress or thin boards to fit spaces; redesign the cavity or cavity width instead
- Avoid contact with incompatible solvents or adhesives
Performance and maintenance
Once installed and properly covered, PIR insulation requires no routine maintenance. The thermal performance of 0.022 W/mK remains stable throughout the product's service life, typically 50+ years in protected applications. The foil facing and compressive strength of 175 kPa mean boards will not settle or degrade under normal building loads. In retrofit projects, ensure ventilation paths are not blocked by insulation, particularly in pitched roofs where rafter vents or soffit ventilation must remain clear. Inspect boards periodically during construction to confirm they remain dry and undamaged before final coverings are applied.
- No routine maintenance required once installed and covered
- Thermal performance remains constant over the building's life
- Maintain ventilation paths in roof applications to prevent condensation
- Inspect before covering to confirm boards are dry and undamaged