Triple-glazed windows and insulated frames ensure that interior window surfaces are never cold to the touch.

Low-Emissivity (Low-E) glass, with argon or krypton gas between the panes, is used. Learn more about Low-E glass here. The Passive House Institute (PHI) also specifies a U-value of 0.80W/(m²K) or less – a specification easily met by most of our triple-glazed range. You can download full PHPP for our Passive House product range here.

Thermal insulation is usually considered the most important requirement in the design and building process of a Passive House.

All opaque surfaces of a building must have u-values of 0.15 W/(m²K) or less. This keeps warmth in during winter and heat out during summer.

Adequate ventilation - with heat recovery - circulates fresh air through the building and ensures that it remains at or near room temperature.

This prevents the kind of stuffiness you’ll remember from the wintertime years of closed windows in school classrooms and avoids a heat-trap situation in warmer temperatures. A Mechanical Heat Ventilation Recovery (MHVR) system helps to keep both excessive heat and cold very firmly to a minimum.

Passive houses are designed to have a continuous airtight outer shell. Leakage through any gaps must be less than 0.6 of the total house volume, per hour, at 50 Pascals pressure.

This rate is known as Air Changes per Hour (ACH50) and is measured in a process known as a blower door test. It requires airtightness to be around 20x that of a standard build – allowing for clear comfort benefits that include reducing draughts and cold spots.

Crucially, the longevity of a building is also improved. Indoor air always has a higher water vapour content than outdoor air – and so, when draught spots are not eliminated, the condensation caused by air cooled as it leaves the building can cause moisture problems that weaken the building components. 

Passive Houses are designed to reduce or eliminate thermal bridging, especially in cooler climates.

Thermal bridging refers to an area or object that is more conductive than the materials around it. Heat follows the path of least resistance, so thermal bridging generally means that we have more heat loss and colder interior surface temperatures. An example of a classic thermal bridge spot: insufficient insulation is detailed below a door or window frame.

The interior surfaces are barely separated from the cold exterior face of the building and all manner of cold and damp spots ensue. How do Passive House requirements tackle this? Detailed planning is required to eliminate thermal bridging wherever and minimise their impact where some thermal bridging is unavoidable. Technical details of the thermal bridging requirements can be found here.