Passivhaus Wall Details
The following article contains excerpts, details and information from our book Understanding Passivhaus – The Simple Guide to Passivhaus Detailing and Design.
Windows perform a variety of functions in any building. They provide natural light, ventilation, a connection to the outside, sunlight, sound insulation and so on. In a Passivhaus, the windows also play a key role in the overall performance of the building. Thermal performance of the windows is a required standard of the Passivhaus.
The windows in a Passivhaus play a vital part in reducing energy demand by taking advantage of passive solar design strategies. High performance windows still have heat and energy losses much higher than the surrounding building envelope.
A U-value is used to measure the thermal efficiency of the window. The lower the U-value the better the thermal performance. A Passivhaus window must achieve a whole window U-value of 0.80W/m2k.
This low U-value keeps the internal temperature of the window at a comfortable level, removing any need to provide a heat source close to the window. The average temperature of the internal window surface should not fall below 17 ̊C on a cold day.
Be sure to double check manufacturer information with regards to U-values. Some refer to the U-value of the centre of the pane, while others will give an overall window U-value which includes the frame. Thermally, the weakest point of every window is the window spacer, usually made of aluminium. Designers are now specifying windows that have warm edge spacers made from thin stainless steel or thermoplastic material which considerably improve the overall window performance.
Installation and positioning of the windows within the building envelope is key to ensuring the windows perform at their optimum level. Thermal bridges can occur if a window is installed incorrectly. The Passivhaus method is to place the window within the insulation layer of the wall to minimise thermal bridging. This means that the insulation is extended so that it overlaps the window frame. This helps to prevent any heat loss and raises the internal temperature. The installation of airtight tapes must also be carried out correctly in order to ensure the airtightness layer remains continuous.
Due to the nature of the building envelope, the windows can have very deep reveals. This can benefit the building by reducing solar gains during summer and minimising overheating, however, it is important to make sure the reveals do not prevent solar radiation in winter.
Passivhaus Window Details Examples
Passivhaus Certified Windows
Comar Aluminium window – Comar 10
Green Building Store – Ultra Insulated
The image below shows a selection of validated installations from the Certified Passive House Component Certificate.
Of course there are many other Passivhaus certified windows available to the UK market from Europe and beyond.
You can find the full list on the Passivhaus Database here:
Other Passivhaus Window Details Resources
Excellent article by Elrond Burrell all about the Passivhaus Window
Passivhaus Window U-Values
How to Build a Passivhaus – Passivhaus Trust
You might also be interested in: