Energy efficient and healthy social housing with a 7-star rating

The case study explores 2 kinds of higher-performing homes that have been built through a social housing project in Sunshine, Melbourne.

This innovative project is a partnership between Homes Victoria – part of the Victorian Department of Families, Fairness and Housing (DFFH) – and Baptcare Affordable Housing, with Creation Homes as the builder. The project consists of 20 new homes, with 12 homes built to the DFFH Housing Design Guidelines and 8 built to a higher Passive House design standard.

By building to these higher levels of energy performance, this project is delivering homes that Geraldine Lannon, Baptcare CEO says will mean “social housing tenants will have lower power bills and a safer and cleaner environment”.

Reflecting industry best practice: the DFFH guidelines

The DFFH guidelines are a requirement for all new social and affordable housing projects in Victoria. They stipulate the required level of adaptability and accessibility to enable access and provide amenity for their clients and to facilitate modification if required in the future. The Housing Guidelines reflect best practice in the affordable housing construction industry and demonstrate care for the tenants regarding amenity, safety and vulnerability to rising energy and water costs.

Since 2018, Homes Victoria have outlined the sustainable design requirements for new low rise housing properties in Victoria to have the following:

• achieve a Nationwide House Energy Rating Scheme (NatHERS) rating above the minimum 6 stars required under regulation
• are all electric fuelled (no gas connection)
• have solar photovoltaic (PV) cells.

This currently equates to achieving a minimum rating of 7 stars under NatHERS for all new dwellings. In achieving this rating, Homes Victoria requires that good passive solar design and low costs building envelope features be prioritised over higher cost inclusions. The guidelines advise that designing effective cross ventilation and shading strategies and specifying energy efficient fixed appliances should be considered, in addition to the following:

• principal living area orientation to the north
• minimisation of west facing glazing
• protection of windows from direct summer sun
• utilisation of efficient insulation and construction systems in floors, walls and ceilings and utilisation of party wall construction
• building air tightness measures
• quality glazing and framing systems.

These sustainable design requirements mean that the homes built by Homes Victoria all meet the requirements of Sustainability Victoria’s 7 Star Homes program and were able to be tested for as-built verification. In the Baptcare Affordable Housing development, 12 out of the 20 homes were built to this standard and 8 exceeded this standard by meeting the requirements for Passive House.

Going a step further: the Passive House standard

Baptcare Affordable Housing chose to take 8 of the homes in this development to the Passive House or ‘Passivhaus’ standard with the intent to pilot the health benefits to its tenants and minimise the home’s energy requirement. The Passive House construction methodologies reduce the risks of poor air quality and mould in the home while also achieving thermal comfort for the residents which is ideal for residents with chronic health conditions.

Passive House sets an internationally recognised criteria for thermal comfort, minimum fresh air rates, and limits on energy consumption for heating and cooling. The Passive House standard is designed to ensure certified buildings perform as expected, providing higher levels comfort, air quality and efficiency, while also avoiding condensation. Passive House represents international best practice in building construction.

For a home to meet the Passive House standard it must address 5 key principles of healthy and efficient homes. It should focus on airtightness (under 0.6 ACH-1@50Pa), ventilation, continuous thermal insulation, thermal bridge free design and high-performance doors and windows designed to reduce the amount of heating and cooling required. Passive House buildings allow for energy savings of up to 90% compared with typical existing buildings and over 75% compared with average new best-practice constructions. Below is a table demonstrating the key differences between the Passive House standard and the 7 star homes standard.

Home features

Table 1: Comparing a 6-star baseline home to DFFH’s design standards for 7-star and Passive House standard.

Air tightness

Uncontrolled air leakage can significantly reduce the energy efficiency of a house. Decreasing uncontrolled air leakage can prevent heat loss in winter and the entry of warm air in summer. The air leakage rate of a house is measured by the number of times in an hour the air inside the house is replaced with outside air – air changes per hour or ACH-1. These air leakage rates are measured using a blower door test. The test involves mounting a large fan in a door to pressurise a house and measuring air leakage rates at a range of different pressure levels. External doors and windows must be closed during the test.

The National Construction Code (NCC) does not currently quantify an air leakage rate for new buildings or major renovations. Instead, new single dwellings that are constructed to NCC performance requirements and assessed using Nationwide House Energy Rating Scheme (NatHERS) software are assumed to achieve a permeability rating of 10m³/hr.m² (a measure of air leakage through a square metre of building envelope). This is broadly equivalent to 10 air changes per hour (ACH^-1) at 50 Pa when applied to detached homes.

Sustainability Victoria collaborated with Baptcare Affordable Housing and Homes Victoria to engage an as-built verification assessor to test the 7-star NatHERS rated homes through airtightness testing and thermography; the results are shown below:

The 8 units built to the Passive House standard also received independent as-built verification in order to meet the rigorous certification standard. A Passive House needs to be airtight, so a blower door test was undertaken at both the lock up and completion stages. The homes needed to attain an air tightness result of less than 0.6 ACH-1 at 50Pa to meet the Passive House criteria. During the test the building was checked for trace points of potential air leakage using theatrical smoke and the homes successfully achieved the Passive house airtightness target.

Within Sustainability Victoria’s 7-star homes program there are also a handful of homes being built to the Passive House standard which have achieved air tightness results between 0.26 to 0.50 m3/h/m2 @50Pa.

Ventilation strategies

Ventilating a home can typically be achieved by creating air movement through the house, called natural ventilation. When high levels of air tightness are achieved, generally reaching below 5ACH-1 @50Pa adequate ventilation strategies are of vital importance to ensure the internal air quality of the home.

NCC 2022 H6V3(2) requires mechanical ventilation “Where an air permeability of not more than 5 m3/hr.m2 at 50 Pa reference pressure is achieved”.

Natural ventilation is a key requirement of the homes built in the 7 Star Homes program, allowing for windows to be opened to capture breezes and exchange the air in the home. Additionally, all exhaust fans venting from the kitchen and the wet rooms are ducted directly to the outside rather than into the roof cavity. This requirement will avoid the risks of mould and mildew building up in the homes. The Master Builders Association of Victoria have developed an informative brochure on avoiding condensation.

The ultimate solution to indoor air quality is to use a Mechanical Heat Recovery Ventilator (MHRV) and these systems are required in all homes which are achieving the Passive House standard. A MHRV draws fresh air from outside through a heat exchange system that warms (in winter) or cools (in summer) the incoming air with air from within the house. This means that fresh air can be introduced with much lower net heat loss. MHRV systems can also contain filters to eliminate contaminants from outdoor air such as pollen and pollution and dehumidifiers to help eliminate mould.

While MHRVs are not cheap, they are an excellent solution for highly efficient houses and cases where the occupants suffer from allergies and respiratory conditions. The Sunshine passive house units have a mechanical heat recovery ventilation system installed which supplies fresh tempered air to the living areas and bedrooms with extraction vents to draw out stale and unhealthy air from the home.

Conclusion

These efficient and healthy 7-star and Passive House homes will ensure maximum, long-term energy efficiency for their residents and minimise the impact of energy costs. There are also additional benefits for these social housing tenants than just cost savings – their homes will have comfort, quality and durability for a long time to come.

More information

Learn more about Insulation installation and air tightness

The Australian Passive House Association (APHA) has a FREE guide to Passive House building in Australia available to download.