Net-zero energy homes use natural energy sources and are designed to consume less energy and as such are considered important in the fight against climate change. To be considered a passive house, a building must meet the following criteria:

1. Energy consumption for space heating must not exceed 15 kWh per square meter of net living area (treated floor area) per year or 10 W per square meter of peak consumption.

In climates where active cooling is required, the energy consumption requirement for space cooling roughly matches the higher heating requirements, with an additional contribution for dehumidification.

2. Renewable primary energy consumption from renewable sources (PER according to the PHI method) – the total energy to be used for all domestic applications (heating, hot water and domestic electricity) must not exceed 60 kWh per square meter of treated floor area per year for a Passive House Classic.

3. Airtightness – maximum 0.6 air changes per hour at a pressure of 50 Pascals (ACH50), as verified by on-site pressure testing (in both pressurized and unpressurized conditions).

4. Thermal comfort must be met for all living spaces in both winter and summer, with no more than 10 % hours in a given year being above 25 °C.

Passive House buildings are planned, optimized and verified using the Passive House Planning Package (PHPP).

All of the above criteria are achieved through intelligent design and implementation of the five passive house principles:

1. Design without thermal bridges

2. Top-notch windows

3. Ventilation with heat recovery

4. Quality insulation

5. Airtight construction

The following five basic principles apply when building passive houses:

1. Thermal insulation

All opaque building elements of the external envelope of the house must be very well insulated. For most cold and warm climates this means a heat transfer coefficient (U-value) of maximum 0.15 W/(m²K), i.e. maximum 0.15 watts are lost per degree of temperature difference and per square meter of external surface.

2. Windows for passive houses

Window frames must be well insulated and fitted with low-energy glass filled with argon or krypton to prevent heat transfer. For most cold and warm climates this means a U-value of 0.80 W/(m²K) or less, with g-values around 50 % (g-value = total solar transmittance, the proportion of solar energy available to the room).

3. Heat recovery from ventilation

The key is effective ventilation with heat recovery, which enables good indoor air quality and saves energy. In a passive house, at least 75 % of heat from the exhaust air is transferred back to the fresh air using a heat exchanger.

4. Airtightness of the building

Uncontrolled air leakage through gaps must be less than 0.6 air changes per hour during a pressure test at 50 Pascal (in both pressurized and unpressurized conditions).

5. Absence of thermal bridges

All edges, corners, connections and transitions must be planned and implemented with great care to avoid thermal bridges. Thermal bridges that cannot be avoided must be minimized as much as possible.

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