What do we mean by Passive House?
Passive House (also known as Passivhaus) is a building standard that uses sustainable design and construction to create a building which is truly energy efficient, comfortable, affordable and ecological at the same time.
Passive houses have consistently good air quality and very low energy consumption. In the United Kingdom, an average new house built to the Passive House standard would use 77% less energy for space heating, compared to the circa-2006 Building Regulations.
There are three basic requirements for a passive house:
- needs to have heating demands lower than 15 kWh per square meter annually (kWh/m²a).
- needs to have primary energy demands (such as warm water, heating, house appliances) lower than 120 kWh/m²a.
- must pass a pressure test and the pressure must be limited to 50 Pascals with the pressure differential not exceeding 0.6 times a room’s volume per hour (n50 < 0.6 h-1).
What are the key features of a passive house?
Using solar gains
Using the building orientation and mass correctly allows for the maximisation of solar gains, by making solar radiation the primary heating source for the building. As a space is heated by the sun shining in through the windows, it reduces the need for heating via mechanical means (i.e. radiators).
Good daylight and shading
Natural light is free and good for you, as we outlined in a previous post. Passive House design makes use of windows and the orientation of the building to maximise natural light, therefore reducing the need for artificial lighting and reducing energy bills.
Natural ventilation and shading allow for natural cooling. Being able to open windows at night allows cooler air to flow into the building, naturally reducing the temperature and reducing the need for the use of fans, for example. In summer, solar shading can provide additional help for keeping a building cool.
High levels of insulation
Around 70% of heat loss occurs through the external walls and roof of a house. In Passive House design, high levels of insulation are used to minimise this heat loss and save energy.
Passive Houses are designed to be airtight, meaning that they are draught-free and prevent the build up of moisture in the building. This means lower heating bills and helps to eliminate damage caused by moisture and damp.
How much does a passive house cost?
In order for a passive house to be able to have such low energy demands, it needs to be built in a certain way. Passive Houses can often be more expensive than traditional houses due to the following reasons:
- Amount of insulation is required
- Addressing airtightness issues may require higher quality products to be specified
- Mechanical ventilation is often a requirement
That said, the difference in usage for heating, hot water, ventilation and overall household electricity usage are very clear to see: