What is a Passivhaus?
A Passivhaus is designed for ultra-low energy consumption combined with consistently good internal air quality.
A Passivhaus is not about lots of advanced technology; rather, it is about changing the way we build. This means integrating design for low energy into the plans from day one, designing with an awareness of the impact of form factor, eliminating thermal bridges and radically reducing air leakage compared with standard builds, incorporating additional insulation and making use of solar gain.
From early in the design process, special energy modelling software – the Passivhaus Planning Package – is used to calculate how the proposed design will perform and a proven track record stretching back over two decades shows that the predicted performance is achieved in real life. This is something non-Passivhaus low energy builds often fail to achieve.
A Passivhaus uses around 90% less energy for heating than a typical building and 75% less than typical new builds. The air leakage rate (expressed in air-changes per hour @ 50Pa -ach@50Pa) is 0.6 or less. In a typical UK building it is over 10 ach@50 Pa.
Fresh air is introduced via a heat recovery ventilation system (MVHR) which removes the heat from the stale outgoing air which would normally be lost in a leaky conventional build. MVHR systems typically save upto 16.5kWh of heat for every 1 kWh of electricity used to run the system.
Triple glazed timber windows which are Passivhaus suitable and continue to perform well into the future ensure that there is no cold radiant close to the glass. This means there are no drafts coming off the windows and allows the full extent of the floor space to be utilised even when the temperature outside is -10°C.
You can read more about the Passivhaus standard and how to achieve it in The Passivhaus Handbook
Less energy for heating than a typical building
The same block of flats before and after being upgraded to the Passivhaus standard. Energy loss shown by the bright colours is greatly reduced. Improved levels of insulation, installed without gaps to minimise cold bridges and the use of triple glazed windows has transformed this residential block, reducing CO2 emissions and the residents heating bills.
Passivhaus Certification is an independent quality control process that gives you assurance that your home will genuinely perform as claimed. Passivhaus Certification of your home is voluntary but will give you peace of mind and will, we believe, add value to your home in the future. Certification is a process that runs throughout the design and construction phases. It is always undertaken by an external, Passivhaus Institute accredited Certifier.
Certification applies to completed whole buildings. Components, such as windows and heat recovery ventilation (MVHR) units used within a building and people in the team that design a Passivhaus are also certified. However, it is not necessary that all components used within the build are certified so long as they are Passivhaus suitable. The exception is for heat recovery ventilation units (MVHR) units, where we recommend that only certified models are used, as the performance of the MVHR is critical to the performance of the whole building.
Likewise, it is essential that the people doing the design and energy modelling have demonstrated their competence. The best way to do this currently is through the Certified Passivhaus Designer qualification.
The Benefits of the Passivhaus Standard
ultra low fuel bills and much less exposure to energy price rises
unrivalled indoor comfort – no drafts or cold spots in winter
improved indoor air quality bringing many potential health benefits
quieter indoor space when the triple glazed windows are closed
lower maintenance costs – less technology to go wrong
greater building fabric durability
huge variety of styles, layouts and materials that can be employed