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UK Vapour Resistance Values Reference
Vapour resistivity and vapour resistance values for common building materials including plasterboard, OSB, PIR, breather membranes and VCLs.
Vapour Resistivity of Common Building Materials
Higher values = more resistant to vapour flow. Vapour resistance of a layer = resistivity x thickness (m).
| Material | Vapour Resistivity (MNs/gm) | Notes |
|---|---|---|
| Aluminium foil | Very high (effectively infinite) | Used as VCL when sealed at joints |
| Polythene sheet (250 mu) | ~110,000 | Common VCL/DPM material |
| PIR/PUR insulation (foil-faced) | ~100–150 | Foil facings add significant vapour resistance |
| XPS insulation | ~150–600 | High vapour resistance, used below ground |
| EPS insulation | ~25–100 | Moderate vapour resistance |
| OSB/3 (9-11 mm) | ~30–80 | Acts as partial vapour check in timber frame |
| Plywood (softwood) | ~15–50 | Moderate resistance |
| Plasterboard (standard) | ~4–8 | Low — does not serve as VCL |
| Plasterboard (foil-backed) | High (foil-dependent) | Foil backing acts as VCL if joints sealed |
| Mineral wool insulation | ~5 | Very low — vapour passes through readily |
| Brick (engineering) | ~25–100 | Dense, moderate resistance |
| Brick (facing, common) | ~15–40 | Variable by type and porosity |
| Dense concrete block | ~15–30 | Moderate resistance |
| Aerated concrete block | ~8–15 | Lower resistance due to air cells |
| Cement render | ~25–50 | Moderate resistance |
| Lime render / lime plaster | ~8–15 | Breathable — suitable for heritage buildings |
| Breather membrane (standard) | ~0.3–0.6 | Very low — allows vapour to escape outward |
Typical Vapour Resistance of Specific Layers
| Layer | Thickness (mm) | Vapour Resistance (MNs/g) |
|---|---|---|
| 250 mu polythene VCL | 0.25 | ~25–50 |
| 12.5 mm plasterboard | 12.5 | ~0.06–0.10 |
| 9 mm OSB/3 | 9 | ~0.27–0.72 |
| 100 mm mineral wool | 100 | ~0.50 |
| Breather membrane | ~0.5 | ~0.03–0.06 |
Related Calculators
See the Insulation Lambda Values for thermal conductivity, or the Insulation U-Values for Part L compliance targets.
Frequently Asked Questions
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Part L 2021 U-Value Targets
Part L 2021 target U-values for all building elements with notional dwelling values.
Part B Fire Resistance Ratings
AD-B fire resistance periods: 30, 60, 90, 120 min ratings by building type for walls, floors, doors and structural elements.
UK Brick Types
Facing, engineering (Class A, B), common, London stock and Fletton bricks with strength and frost resistance.
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Last updated: April 2026
Verified against UK standards · estimates only, confirm with your supplier.