Passive House Design

The house must be well sealed. The building envelope creates a solid air barrier, so no air leaks in or out giving full control over the internal environment and significantly improving thermal comfort, (windows are still openable though).

Sufficient insulation is required within the building’s envelope, providing enough thermal separation between the heated, or cooled, conditioned inside environment and the outdoors. This improves thermal comfort and reduces the risk of condensation.

An airtight building needs reliable source of fresh air for both human comfort and building longevity. Good ventilation is essential as it prevents accumulation of handful contaminants such CO2, volatile organic compounds (VOCs) and excess moisture which can lead to mould growth. In traditional buildings, fresh air enters the building through a series of vents and through infiltration or draft. This system is uncontrolled and cannot guarantee even ventilation throughout the building. In a Passivhaus mechanical ventilation is combined with heat recovery, known as Mechanical Ventilation Heat Recovery (MVHR). It uses the thermal energy within the building to pre-heat or pre-cool (depending on the season) incoming fresh air, ensuring clean, filtered air is provided regardless of outdoor conditions.

The insulation not only needs to be sufficient in thickness but also needs to be continuous. This means keeping penetration through the insulation to an absolute minimum, and if unavoidable then using materials that are less conductive to heat (eg. timber instead of metal) and/or incorporating thermal break to avoid thermal bridges.

Thermal bridges are the points at which a conventional house loses energy. They are often unaccounted weak points in the building fabric, resulting in high local discomfort, moisture and mould, while providing a highway for energy loss between the interior and the exterior of the house that.