Low Carbon Design
Low carbon design is now the corner stone of all new building work within the UK. Part L and SAP provide a platform in which regulations can be tightened, amended and brought into mainstream, so that we can produce more energy efficient buildings. PassivHaus is a similar set of standards, already in existance and out performings Part L and SAP in many areas.
A comparison between the two sets of regulations is below. Information taken from www.PassivHaus.org.uk.
| PassivHaus | UK Part L | |
| 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 |