"Passivhaus" or "Passive House" buildings are designed to provide occupant comfort while using very little energy for heating or cooling. They are designed and built according to principles developed by the Passivhaus Institute in Germany, and are certified through a rigorous quality assurance process.
Passivhaus designed buildings can reduce space heating requirements by 75%, compared to standard practice new builds in the UK. Designing your new home to the Passivhaus standard will reduce your carbon emissions and save you money on heating bills.
Passivhaus construction is a voluntary low-energy standard. There are three main aims to Passivhaus design;
1. minimise heat loss through the building fabric
2. minimise ventilation heat loss by controlling the ventilation
3. Optimise solar heat gain to warm the building in winter
The Passivhaus standard
To achieve the Passivhaus Standard the building must meet the technical criteria set by the Passivhaus Institute.
1. Super insulation of the building fabric. The ground floor, external walls and the roof, must be designed to limit the heat loss to a much higher standard than the current building regulations in the UK. Fabric U-values (thermal resistance) must be 0.15 W/m²·K or better.
2. High Performance Glazing is required which is typically triple glazing with low-E coatings and warm edge spacers.
3. The construction must be Thermal Bridge free to eliminate heat loss through the external envelope.
4. The shape and form of the building should be compact to reduce the extent of external envelope and reduce heat loss.
5. A continuous air tight layer is required around the external envelope to achieve an airtightness of 0.6 air changes per hour (at 50 Pascals pressure) or better.
6. Mechanical Ventilation with Heat Recovery (MVHR) is required to provide high quality fresh air without heat loss. MVHR systems must be at least 75% efficient.
7. Orientation of windows should maximise solar heat gain in winter.
8. Thermal comfort must be achieved for all living areas, all year-round, with not more than 10% of the hours in any given year reaching a temperature over 25°C.
Image by passipedia.org
Simply designing to the Passivhaus standard alone is not enough to achieve Passivhaus Certification.
Accurate design modelling, using the Passive House Planning Package (PHPP), is required to demonstrate the energy use of the building.
The Passivhaus Standard requires a predicted space heating demand of 15kWh/m² per annum per square meter of usable floor area. The average existing UK house uses around 200kWh/m² per annum and a new-build house may range from 50-100 kWh/m² per annum.
The Primary Energy demand should not exceed 120kWh annually for all domestic applications (heating, cooling, hot water and domestic electricity) per square meter of usable floor area.
A Classic Passivhaus is a low energy building, but if the building can also generate as must energy as it uses, using PV panels for example, then is becomes a Passivhaus Plus.
A Passivhaus Premium building is for the more ambitious client who wants a building to generate far more energy than it will use.
The Passivhaus standard can also be applied to retrofit projects to achieve similar savings in space heating requirements. The EnerPHit standard is for the refurbishment of existing buildings which cannot achieve Passivhaus Standard due to the existing building form, existing orientation or existing context.
If you would like to live or work in a Passivhaus building we would approach the design, the technical detailing and construction with this aim in mind. The Passive House Planning Package (PHPP) is used to model the building to verify that the Passivhaus Standard will be met.
A Passivhaus Certifier is required at an early stage in the process. Design and technical information and the PHPP are submitted to the Passivhaus Certifier to assess the detailed design. Supporting information, such as air test results, ventilation commissioning, construction photographs, are also required for Certification of a Passivhaus building.
We must by law comply with the Building Regulations but we can build to a better standard than this.
The building regulations requirements include minimum thermal insulation levels, maximum air leakage levels and state that buildings must have a permanent source of heating and hot water supply. But there is evidence that completed new buildings don't perform as well as anticipated. There is a Performance Gap.
Studies have shown that building to the Passivhaus Standard will result in a better quality construction and reduce the building Performance Gap. A significant number of Passivhaus buildings have been monitored and have demonstrated that they perform, in terms of energy consumption, as predicted. The certification of a Passivhaus building using an accredited Passivhaus Certifier will provide assurance to clients that new buildings are built to a higher standard.