Outline specification for a PassivHaus in the UK
Please note that the following information is for guidance only, compliance with the PassivHaus standard must be assessed using the PassivHaus Planning Package. The PassivHaus Institut also has an informative checklist which outlines the typical process undertaken to achieve PassivHaus.
| PassivHaus Standard | UK new-build common practice | |
| Compact form and good insulation: | All components of the exterior shell of a PassivHaus are insulated to achieve a U-Value that does not exceed 0.15 W/m2/K | Limiting U-values of approximately 0.25-0.35 W/m2/K |
| Southern orientation and shade considerations: | Passive use of solar energy is a significant factor in PassivHaus design. | Some consideration is given with regard to north/south orientation, but the improved energy savings resulting from passive site design are often overlooked. |
| Energy-efficient window glazing and frames: | Windows should have U-values not exceeding 0.80 W/m².K for both glazing and frames - this requires the window frame to incorporate insulation and the glazing to be triple. Solar Heat Gain Co-efficient through the glazing should be at least 50%1. | 1.8-2.2 W/m2K typical |
| Building envelope air-tightness: | Air leakage (n50) through unwanted gaps and cracks in the building fabric must be less than 0.6 times the house volume per hour under negative and positive pressurisation. | Design air permeability of 7 to 10 m2/hr/m3@ 50 Pa. This is approximately a factor of 10 poorer than the PassivHaus standard. Research has also shown that air permeability values for completed dwellings frequently exceed these design limits. |
| Passive preheating of fresh air: | Fresh air may be brought into the house through underground ducts that exchange heat with the soil. This preheats fresh air to a temperature above 5°C (41°F), even on cold winter days. | The majority of new-builds do not achieve good enough air permeability values to warrant the incorporation of a whole house ventilation system - thus trickle vents, extract fans, or passive stack ventilation is commonly used. |
| Highly efficient heat recovery from exhaust air using an air-to-air heat exchanger: | Most of the perceptible heat in the exhaust air is transferred to the incoming fresh air (heat recovery rate over 80%). | |
| Energy-saving household appliances: | Low energy refrigerators, stoves, freezers, lamps, washers, dryers, etc. are indispensable in a PassivHaus. | Dedicated low-energy lights are provided in a number of rooms in a new dwelling - if appliances are supplied they will be generally C-rated or perhaps 'Energy Saving Recommended' in some instances (as these are widely available). |
| Total energy demand for space heating and cooling | Less than 15 kWh/m2/yr | Typically 55 kWh/m2/yr |
1The Solar Heat Gain Co-efficient (SHGC) is provided as a guide, it can be adjusted for glazing on different facades. This can help either reduce heat loss on sheltered sides/ north facing glazing, or alternatively help to reduce the likelihood of overheating when specified in conjunction with other features/strategies (please note that the SHGC of a window usually decreases as the U-value improves).
PassivHausUK is registered with the PassivHaus Institut Darmstadt as their official UK certifier for PassivHaus projects.