PIR (Polyisocyanurate) is a rigid board insulation material with one of the lowest lambda values on the market (0.023 W/m·K). This means you achieve a high insulation value with a thin board. PIR boards are rigid, lightweight, and widely used for roof, floor, and wall insulation.
Properties
| Property | PIR |
|---|---|
| Lambda (λ) | 0.023 W/m·K |
| R-value at 100 mm | 4.35 m²·K/W |
| Moisture resistant | Yes (closed cell structure) |
| Compressive strength | Good (walkable) |
| Fire class | B-s1, d0 (difficult to ignite) |
| Weight | Light (~30 kg/m³) |
Where is PIR used?
| Application | Advantage |
|---|---|
| Flat roof | Tapered boards (with built-in slope) available |
| Pitched roof (above rafters) | Thin layer, high R-value |
| Floor insulation | Pressure-resistant, suitable under screed |
| Timber frame (supplementary) | Additional insulation on the outside of the studs |
| Cavity | Thin board, high R-value — ideal with limited cavity width |
PIR for DIY projects
Flat roof (garage, garden shed)
PIR tapered boards are ideal: insulation + slope in one product.
1. Vapour barrier on the roof deck
2. Glue PIR boards (with taper) using PU adhesive
3. EPDM membrane on top
Floor insulation
1. Foil on the subfloor
2. Lay PIR boards tightly together
3. Tape the joints
4. Screed or dry-build system on top
Wall insulation (from the inside)
1. Glue PIR boards to the wall
2. Tape joints (vapour barrier)
3. Glue plasterboard on top or mount on battens
Standard dimensions
| Board size | Thicknesses (mm) |
|---|---|
| 120 x 60 cm | 30, 40, 50, 60, 80, 100, 120, 140 mm |
| With aluminium facing | Standard (built-in vapour retarder) |
| With taper | Thickness varies across the board |
PIR vs. other insulation materials
| PIR | EPS | XPS | Mineral wool | |
|---|---|---|---|---|
| Lambda (λ) | 0.023 | 0.032 | 0.035 | 0.035 |
| R-value at 100 mm | 4.35 | 3.13 | 2.86 | 2.86 |
| Moisture resistant | Yes | Limited | Yes | No |
| Compressive strength | Good | Moderate | Very good | No |
| Price | High | Low | Medium | Medium |
| Fire resistant | Moderate | Poor | Poor | Excellent |
Related terms
- R-value
- Mineral wool
- Flat roof
- Roof slope
- EPDM