What This Requirement Covers
Passivhaus (Passive House) is a voluntary energy performance standard developed in Germany that achieves extremely low energy consumption through a fabric-first approach. While not a Building Regulations requirement, Passivhaus principles increasingly influence UK building design and align with the direction of the Future Homes Standard.
Key Requirements
Passivhaus Performance Targets
- Space heating demand: Maximum 15 kWh/m²/year (approximately 90% less than a typical UK new-build)
- Primary energy demand: Maximum 120 kWh/m²/year (total energy including heating, hot water, lighting, and appliances)
- Airtightness: Maximum 0.6 ACH at 50 Pa (approximately 10 times more airtight than the Part L 2021 maximum of 8 m³/(h.m²))
- Overheating: Indoor temperature must not exceed 25°C for more than 10% of the year
Key Design Principles
- Superinsulation: U-values of 0.10-0.15 W/m²K for walls, 0.10 W/m²K for roofs, and 0.08-0.12 W/m²K for floors
- Triple glazing: Window U-values of 0.6-0.8 W/m²K with high-performance frames
- Extreme airtightness: Careful detailing and rigorous testing to achieve 0.6 ACH
- Thermal bridge-free design: All junctions designed to eliminate thermal bridges
- MVHR: High-efficiency heat recovery ventilation (90%+ recovery) providing all ventilation
- Solar orientation: Maximising passive solar gain in winter while controlling it in summer
Passivhaus vs Part L 2021
| Metric | Part L 2021 | Passivhaus |
|---|---|---|
| Wall U-value | 0.26 W/m²K | 0.10-0.15 W/m²K |
| Air permeability | 8 m³/(h.m²) | ~1 m³/(h.m²) |
| Glazing U-value | 1.6 W/m²K | 0.6-0.8 W/m²K |
| MVHR required | No (System 4 optional) | Yes (90%+ recovery) |
Practical Compliance Tips
- Passivhaus certification requires design and construction oversight by a certified Passivhaus designer and consultant
- The additional construction cost is typically 5-15% above standard Part L compliance, but running costs are dramatically lower
- MVHR is essential in Passivhaus buildings; the building is too airtight for natural ventilation alone
- Thermal bridge-free details are critical; a single thermal bridge can significantly increase the heating demand
- Consider Passivhaus principles even if not seeking certification; the fabric-first approach delivers long-term energy savings
- The Passivhaus Trust (UK) provides resources, training, and a directory of certified designers
- EnerPHit is the Passivhaus standard for retrofitting existing buildings, with slightly relaxed targets