Fixing and buying guide
Rigid PIR Insulation 1200 x 2400 x 100mm
What this product is for
Rigid PIR insulation boards are used to insulate cavities in walls, suspended timber floors, and roof voids in both new build and retrofit applications. The 100mm thickness is designed to fit standard building cavities whilst delivering the thermal performance required by current building regulations. The moisture-resistant properties make these boards suitable for use in damp-prone areas such as basements and ground floor cavities.
- Cavity wall insulation in new build and refurbishment
- Suspended floor insulation between joists
- Pitched and flat roof insulation
- Retrofit insulation projects
Sizing and coverage
Each board measures 1200mm wide by 2400mm long and 100mm thick. A single board covers 2.88 square metres of surface area. The 100mm thickness is a standard cavity width that fits between timber studs and joists spaced at 400mm, 450mm or 600mm centres. Calculate your total cavity area in square metres and divide by 2.88 to determine the number of boards required, allowing for offcuts and waste.
- Single board area: 2.88 m²
- Board dimensions: 1200 x 2400 x 100mm
- Fits standard timber frame spacing
- Add 5-10% for cutting and waste
Pre-installation checks
Before fixing, ensure the cavity or void is clean and free from debris, dust and moisture. Check that cavity widths are suitable for 100mm boards and that structural supports (studs, joists or rafters) are sound and properly spaced. Inspect the boards on delivery for any damage to edges or faces that could compromise performance. Store boards flat and dry on site, protected from weather and direct sunlight until installation.
- Verify cavity dimensions match 100mm thickness
- Check structural supports are sound and correctly spaced
- Inspect boards for damage on arrival
- Store flat, dry and protected from weather
Fixing and installation
PIR boards are typically fixed using mechanical fixings such as cavity wall ties, insulation board fasteners or friction fit between studs and joists. In cavity walls, boards should be supported on wall ties or cavity battens and secured with appropriate fixings at 400-600mm centres. In floors and roofs, boards can be friction-fitted between joists or secured with adhesive and mechanical fixings. Ensure boards are fitted tightly together to minimise thermal bridging, and seal any gaps with expanding foam or appropriate sealant. Always follow the specific fixing recommendations provided by the board manufacturer.
- Use mechanical fixings at 400-600mm centres
- Fit boards tightly to minimise gaps
- Seal joints with expanding foam or sealant
- Follow manufacturer fixing guidance for your application