Passive House (Passivhaus Certified Design Standard)
The proposed house was built towards the Passivhaus standard. This is a successful European ultra-low energy standard for buildings. Passivhaus buildings use only a fraction of the energy for heating (90% less) compared with houses built to the standards required by current building regulations, and deliver low carbon solutions without needing excessive renewable energy. Where Passivhaus differs from UK building regulations and CSH is the requirement for an absolute level of energy consumption instead of improvement over a more basic specification.
The Passivhaus approach has three main strands:
- Minimise heat loss – compact built form, super insulation and triple glazing.
- Minimise ventilation heat loss – airtight construction and heat recovery ventilation.
- Optimise solar gain for winter heat.
These factors combine to deliver a heating demand that can be met with a minimal heating system (it is recognised that to design a house that needs no heating at all is not economic). As well as very low heating bills, Passivhaus offers comfort and a healthy indoor environment. Attention to detail in design and construction ensures no draughts or cold spots wherever you are in the house. Heat recovery ventilation uses low power fans to provide ample fresh air day and night, warmed to room temperature by a heat exchanger transferring the heat from the exhaust air from kitchen and bathrooms to the incoming air.
Passivhaus is a rigorous energy standard; energy performance must be demonstrated through the use of the Passivhaus energy modelling software, which is specifically designed to model ultra-low energy buildings. This is backed up by air leakage tests and commissioning records of the heat recovery ventilation. The standard requires a predicted heating demand of 15kWh/m².a over the usable floor area, adapted for the local climate (average energy use for UK housing stock is around 200kWh/m².a and new-build ranges from 50-100 kWh/m².a). We have developed the design of the house as a compact plan. This form has minimised the heat loss from the house and enabled gains to be received from its share of winter and summer sunshine. Planning design shows that the house can achieve the certified Passivhaus standard. The insulation levels needed to do this can be met with traditional cavity wall construction or timber combined with triple glazed windows and airtightness provided by wet plaster and the roof vapour control layer.
The Passivhaus standard requires an airtightness of 0.6 ach (air changes per hour) @ 50Pa (current Building Regulations require 10.0 ach @ 50Pa). This high standard ensures draught-free comfort, protects the building fabric from condensation due to leakage of humid air, and ensures that the efficiency of the heat recovery ventilation is not bypassed by leakage ventilation.