Passive House refers to a high standard of energy efficiency in a building. Fundamentally about design, Passive House uses a fabric first approach to construction. This means that the materials used during construction are specifically chosen to maximize the overall performance of the building, rather than rely on additional features like mechanical heating and cooling devices.
Buildings that are constructed to the Passive House Standard are incredibly energy efficient, almost entirely self-reliant in terms of achieving an optimum internal climate, which makes them much cheaper to run. They also have a much cleaner and healthier internal environment than the average building and achieve a much lighter carbon footprint. The Passive House concept relies on 5 key principles of design and a building must meet a stringent list of criteria in order to be certified Passive House.
The 5 Key Design Principles of Passive House
Airtightness: Achieving an airtight building envelope is essential to meet the Passive House Standard. Ensuring there are only a very limited number of gaps and cracks within the envelope means there are no drafts and gives full control over the internal thermal climate, ensuring year-round comfort and better indoor air quality.
Thermal Insulation: Providing the appropriate level of high quality insulation between the building envelope and the outdoor environment ensures a high level of control over the internal thermal climate. Adequate thermal insulation will also reduce the risk of condensation, which as we know, can lead to respiratory issues caused by the growth of harmful mildews.
High Performance Windows: Using double or triple glazed windows is an important step in constructing a Passive House building. These specialised windows are low emissivity, with thermally broken or non-metal frames and their size is dependent on their orientation, so that they may allow solar radiation to penetrate the building during winter for heating purposes, but not so large as to let in too much sun during the hotter months.
Mechanical Ventilation Heat Recovery: Buildings that rely on one of these systems have a much better indoor air quality than a standard building. While you certainly can open the windows on a Passive House building, you do not need to rely on this to bring fresh air into the internal environment. The Mechanical Heat Recovery System continuously circulates fresh, filtered air throughout the building. The system also harnesses the heat from the stale air it extracts from the building and uses it to maintain an optimum internal thermal climate. Massively reducing the chance of condensation and filtering out dusts, pollens and other pollutants means that not only is the internal thermal climate always at an ideal level, but the indoor air quality is far superior to that of a standard building, which in turn leads to a much healthier indoor climate.
Thermal Bridge-Free Construction: Continuous, sufficient insulation with no gaps and minimal penetrations means that there are no “thermal highways” for heat or condensation to penetrate. Where the use of heat conductive materials is unavoidable, then thermal breaks must be created by placing non-conductive material between the two materials that would otherwise react conductively to heat. If these measures are not taken, then control over the internal climate will be greatly reduced, leading to higher energy consumption, increased condensation risk and a building that is more expensive to heat or cool.
Passive House Criteria
A series of quantifiable minimum performance requirements make up the criteria that must be met to achieve Passive House Certification. These requirements are as follows:
Indoor Air Quality: The absolute indoor air humidity levels must not exceed 12 g/kg for more than 20% of the occupied time.
Airtightness: In order to control the internal thermal climate, the building envelope must have an airtightness set at = 0.6 ach (+/- 50 Pascals). Alternatively, air permeability is set at = 0.6m3/hr.m2 (+/- 50 Pascals) for larger buildings.
Occupant Comfort: The air temperature must not exceed 25o C for more than 10% of the occupied time. This ensures that the internal climate stays at the most comfortable level throughout both the warm and cool months.
Annual Space Cooling/Dehumidification Demand/Load: Annual space cooling/dehumidification demand is set at = 15kWh/m2.yr. Alternatively, space cooling load is set at 10W/m2. This represents the demand on the cooling system to maintain a consistent comfortable indoor temperature throughout the year. It is a function of the building fabric thermal performance, the air permeability and the outside air ventilation required for maintaining ideal indoor air quality. It is independent of the proposed mechanical plant efficiencies.
Annual Space Heating Demand/Heating Load: Annual space heating demand is set at = 15kWh/m2.yr. Alternatively, space heating load is set at 10W/m2. As with annual space cooling/dehumidification demand/load, the demand on the heating system to maintain a consistent comfortable indoor temperature throughout the year is independent of the proposed mechanical plant efficiencies and is a function of the building fabric thermal performance, the air permeability and the outside air ventilation required for maintaining ideal indoor air quality.
Annual Primary Energy Demand: Annual primary energy demand is set at = 60kWh/m2.yr. Alternatively with renewables, it is set at = 60kWh/m2.yr. This represents the predicted total energy demand of the building, which includes hot water generation, ventilation, heating, cooling, equipment loads and lighting. It takes into consideration the efficiencies of mechanical plant and any renewable generation (if proposed).
What are the benefits of Passive House?
Health: Surely the most appealing and valuable benefit is in regards to the impact on health that a Passive House building has. With continuously filtered air being circulated throughout the home or building, the indoor air quality is exceptionally high, with little to no dust, pollens or external pollutants being able to penetrate the building envelope. This makes building to Passive House standards a great option for those who value the health of their family and home (all of us), and for those who suffer from respiratory illnesses, asthma and allergies, as well as other illnesses like fibromyalgia.
Financial: Energy costs in Australia are higher than ever and look to continue rising. This puts an enormous financial strain on Australians, as well as contributing to higher levels of stress as we worry how we will pay the electricity bill. A home or building that is built to the Passive House standard relies on a HRV (Heat Recovery Ventilation system) to keep the indoor thermal climate at a comfortable temperature year round, with minimal assistance from mechanical or electrical building service systems. This system runs off just 12 watts of power, around the same amount as the average lightbulb. Combined with the building fabric thermal performance, this system ensures that a Passive House building runs at a fraction of the cost of a standard 6 Star Australian home or building.
Environmental: Due to the nature of its fabric first construction and minimal heating and cooling requirements, the carbon footprint of a building with a Passive House certification is significantly lighter than that of a standard 6 Star home or building. Not only is it better for the people who occupy it, but it is better for the environment too.
Can a Granny Flat be built as Passive House Certified?
Any building that must be transportable cannot be built to Passive House standards. The nature of Passive House is that there are minimal penetrations and no breeches in the external thermal membrane. The building technique is vastly different to that of a transportable building and is simply unable to be applied. Any fixed, solid structure can, however, be built to the Passive House standard. This includes homes, businesses, schools, halls, hospitals and function centers.
Passive House and Premier Homes
As of 2019, Premier Homes and Granny Flats became Certified Passive House builders. We are one of the few building companies in Victoria that have the Certification to build to Passive House standards. We have the only Passive House building on permanent display at our Bayswater North display village. Named Genesis, the display home marks the beginning of an exciting new chapter in Premier Homes’ history and showcases the “inner workings” of a Passive House Certified home. We are enormously proud of this achievement and look forward to our future as a diverse company with a strong commitment to Sustainable Housing. At Premier Homes, we are about keeping families together, now and for the future.