A Passive House requires very little energy to maintain a constant, pleasant temperature. In this sense, such buildings are almost “passive” as they need hardly any active heating or cooling to stay comfortable year-round. Excellent insulation and highly efficient heat recovery systems make this possible. Passive design principles are well known in engineering as effective strategies to achieve a goal with little to no input. Passive security, passive filters, passive cooling and Passive House are examples of the successful implementation of this idea.

Of course, none of the aforementioned applications are completely passive in the strict sense of the term as they each require a minor amount of input to guide the respective processes along the desired course. The concept is not as much about letting things happen without using any energy, though, as it is about intelligent design: reaching the desired goal with minimal use of complex systems and non-renewable resources.

The air infiltration through gaps and joints in a conventional building is perceived as draughts. Such “ventilation” is unreliable and uncomfortable. It is also insufficient to ensure healthy indoor air quality on its own, thus necessitating the opening of windows regularly and for extended periods of time. An airtight building envelope ensures that the ventilation system works as efficiently as possible. Perhaps more importantly, it is also key to preventing moisture damage and mould growth: in conventional buildings, gaps in the building structure allow air to pass through and thereby cool down. This can result in condensate that can put the building at risk. Due to the high level of airtightness, this is not a concern in Passive House buildings!

Windows not only allow daylight to enter the rooms, they also make use of the sun’s energy to warm the building. In cool temperate climates, Passive Houses have noble gas filled, triple-glazed window panes with well-insulated frames. During the winter, such high quality windows let more of the sun‘s thermal energy into the building than they let out. During the warmer months as well as in warmer climates closer to the equator, the sun sits higher in the sky resulting in reduced solar heat gains just when they’re less needed. In most climates, large glazing areas should ideally be oriented towards the equator; windows facing east or west can more easily lead to overheating and provide fewer overall solar gains during the heating period.
Windows need careful planning and, where necessary, appropriate shading. The window specifications needed to achieve the Passive House Standard depend on the local climate conditions.

Of course you can! In a Passive House though, you probably won’t feel the need to do so and it is not necessary throughout most of the year. In conventional buildings, occupants must often open the windows, even if it is particularly cold, windy or wet outside, to tackle stale air as well as odours and moisture arising from used towels, plants and wet clothes among other things. To ensure air quality on par with that of a Passive House, windows in conventional buildings would need to be opened at regular intervals day and night, even during the occupants’ absences. This is simply not feasible and as a result, most homes, schools, and offices are insufficiently ventilated.

Passive Houses are different. The ventilation system provides for high quality indoor air, automatically extracting moisture and thereby clearly improving comfort. The result is a building with no draughts, no cold corners, and a constant supply of fresh air. Fine filters keep dust, pollen, and other particulate materials out, an invaluable advantage for people who suffer from asthma or allergies.

A Passive House building’s very well-insulated walls and roof also serve its occupants well in hot summer conditions by keeping the outdoor heat from entering the building. For the windows, shading in the form of external blinds or sunscreens is critical, as it helps keep the heat from the sun outside. In many cases, cross ventilation through opened windows during cooler periods of the day or night can help passively cool the indoor space. Heat recovery is often not needed during the summer months, and most ventilation systems therefore have a summer-bypass, which helps keep indoor temperatures cool through the summer.

Passive House also functions well in hot and humid climates. In such conditions, many of the same general components and passive strategies, optimised for local conditions, are employed. Ventilation with energy recovery effectively reduces heat and humidity inside the building. In areas where active cooling is a necessity, the application of Passive House principles can dramatically reduce cooling needs.