What is a Passive House?
Passive House is a concept of constructing buildings that are energy efficient and have a healthy and comfortable indoor environment. A comfortable building in Passive House terms, maintains constant temperature, humidity levels and indoor air quality in every area of the building throughout the year with very low energy use. A Passive House is also very quiet thanks to high performance design efficient windows and doors.
Any building can be designed to the Passive House standard including apartment blocks, offices, schools, hospitals and factories etc.
Passive House design
Passive House design is not prescriptive, meaning complete freedom of design, building form, size and materials used so long as the building meets the performance criteria.
Passive House takes into consideration more aesthetics or alternative power sources. It focuses on a healthy living environment and low energy use. Passive House Institute New Zealand is devoted to educating the public and construction sector about the impact of the indoor environment on human health and provides resources on how to design healthy and comfortable buildings by following Passive House standards.
The main principles of Passive House design are:
- Low energy consumption
- Excellent level of insulation
- High performance glazing
- Elimination of thermal bridging
- Heat recovery ventilation
Passive House Features
A Passive House building will not use more than 15kW per square metre, per year for heating and cooling to the recommended indoor temperature as recommended by WHO, 18-21°C. To put this in perspective, “that’s 81% less energy than is used to heat a typical single family home in Auckland to 20 degrees (and 92% less than a single family home in Christchurch)”, according to Jason Quinn, a leading Passive House designer and engineer.*
*Jason E. Quinn, CMEngNZ IntPE (USA), founder and director of Sustainable Engineering Ltd., author of many Passive House publications and a book “Passive House for New Zealand, the warm healthy homes we need” published in 2019 www.sustainableengineering.co.nz
High insulation levels
One of the key features of Passive House design is excellent insulation. The entire building envelope including floor, walls and roof needs to be suitably insulated to create a controllable indoor environment. The higher the level of insulation, the smaller energy loss, meaning that a well-insulated building will not lose heat in winter or gain any in summer. In the long-term, the benefits are low heating/cooling bills while maintaining a comfortable 18 - 25°C throughout the year in any given area of the building. The amount of insulation will vary depending on geographical location e.g. North Island or South Island.
It is important that insulation is installed properly and uninterrupted by any services running in cavities. There are well described methods to ensure the insulation maintains its full R-value for example, double layering insulation in ceilings and walls, also called ‘double skin construction’, which also helps to eliminate thermal bridging.
Elimination of thermal bridging
A thermal bridge occurs when an element of construction allows heat to freely travel from one side to the other side of a building material. Examples of thermal bringing are most commonly joints in floors and walls, walls and roofs and also framing elements, steel beams and other structural components. A thermal bridge results in an overall reduction in thermal performance of a building and can cause spots in construction where condensation occurs.
Passive House design calls for the elimination of any thermal bridging. This is achieved through the design process.
High performance glazing
Windows and doors can transfer a lot of heat in winter and cause unwanted heat gain in summer. It is very important that any glazed area in a Passive House uses high performance products. Windows must be at least double glazed and joinery must be suitable to minimise transmission of heat (high standard thermally broken).
Airtightness is another key feature of a Passive House design. Airtightness prevents air leakage through the building envelope. Airtightness helps insulation work properly by preventing unwanted air movement. It is also crucial in controlling indoor humidity.
Airtightness is achieved by use of smart building membranes or rigid air barriers.
Energy recovery ventilation
Once a building is airtight, mechanical ventilation is required to introduce fresh air and extract stale air. Passive House design requires a very efficient heat exchange ventilation system. Fresh air is drawn from outside (not attic space) and circulated around the house while stale air is extracted out, before this happens the energy (heat) is recovered in a special heat exchange device where it is used to preheat incoming air without mixing the flows. These systems are extremely efficient, recovering about 90% of heat and using only the tiniest amount of energy.