Key points
- Our research has found new Australian homes are 50 per cent more airtight than those tested in 2015.
- Increasing your home’s air tightness is a simple and affordable way to lower energy bills, increase comfort, and improve air quality.
- Poor air tightness can cause draughts, increasing energy bills by up to 20 per cent. Overly airtight homes, without controlled ventilation, can lead to condensation and mould.
Australians are no strangers to extreme weather conditions – many of us are familiar with the discomfort of outdoor air infiltrating our homes during cold snaps or heatwaves.
This highlights the importance of air tightness, which is the practice of sealing our homes to prevent indoor air from escaping and unwanted outdoor air from entering. Improving air tightness is one of the easiest, and most affordable, ways to lower energy bills and stay warmer in winter and cooler in summer.
Our research confirms homes that meet recommended air tightness levels are more comfortable, have lower energy bills, and provide healthier indoor air quality.
Poor air tightness can lead to draughts, which can increase energy bills by up to 20 per cent. However, as air tightness increases, controlled ventilation (such as exhaust fans and ventilation systems) becomes vital to avoid condensation and mould.
Blower door test detectives
Our senior experimental scientist Michael Ambrose recently completed Australia's most comprehensive study on air infiltration rates PDF (5 MB)or "leakiness" in new homes. Until his previous study in 2015, there was little available data in this area.
The study, funded by the Department of Climate Change, Energy, the Environment and Water (DCCEEW), investigated the air tightness, insulation quality and heating/cooling ductwork of 233 Australian homes. These were apartments and houses in Melbourne, Sydney, Canberra, Brisbane and Adelaide. Homes specifically designed for air tightness were excluded.
The research team used a blower door test to analyse a home's permeability, which is how easily air can pass through a structure. The higher the permeability, the leakier the home.
During a blower door test, equipment first sucks air into the home and then blows it out. This creates a pressure differential of 50 Pascals (a unit that measures internal pressure). This pressure mimics a breeze blowing through the home on a windy day. Blower door tests find potential leakage points such as downlights, exhaust fans, floorboards, and door and window weather sealing.
Ideal air tightness for Australian homes
Michael's research found a permeability rate of about 5m³/hr/m²@50Pa is ideal for a new dwelling.
“You want to seal tight and ventilate right," Michael said.
"Very tight homes need a controlled ventilation system, otherwise you can get problems like headaches and nausea from the high carbon dioxide and monoxide levels in the home."
The report found:
- New Australian homes are 50 per cent more air tight than those built nine years ago
- Leakages were found in most new homes, with an average permeability rate of 6.9 m³/hr/m²@50Pa
- Common leakage points included poorly sealed exhaust fans, missing window and door seals, and leaks through heating and cooling ductwork
- Some homes, particularly apartments, were found to be very airtight. This can result in resident health issues if controlled ventilation is not included.
Michael confirmed there are simple and affordable ways to rectify these issues and preventatives measures that can be implemented during construction.
"It’s worthwhile highlighting that the study only tested new homes," Michael said.
"Leaky houses tend to go with age - the older the home, the leakier it is. If older homes were included in this study, the level of leakiness would have skyrocketed.
"Older homes are often around 30m²@50Pa. This is equivalent to changing all the conditioned air in a home every 40 minutes."
What do regulations say about 'leakiness'?
Australia’s National Construction Code (NCC) does not specify an air leakage rate, but it does require that buildings efficiently achieve thermal performance by sealing against air leakage.
The Nationwide House Energy Rating Scheme (NatHERS) provides an energy efficiency star rating for residential buildings, but does not account for air tightness.
"If NatHERS awarded higher star ratings to top performing homes, it could increase the adoption of air pressure testing for new homes and reduce energy requirements," Michael said.
"Increased uptake of blower door testing could improve the residential constructions industry's understanding of air tightness and lead to simple construction practices that result in homes that are more airtight."
The report includes a range of recommendations for Australian building codes:
- Establishing air tightness standards in the NCC
- Requiring controlled ventilation in new buildings, particularly apartments to reduce indoor pollutants and moisture
- Making air barriers, such as buildings wraps mandatory in all new residences
- Providing on-site training and educational resources to connect builders with cost-effective solutions that improve building performance.
Airtight homes are trending
Michael's research shows that when it comes to air tightness, new Australian homes are performing better than ever before.
"Even though there aren't specific regulations or requirements, some homes performed really well with permeability rates below five," Michael said.
"Some homes were unintentionally very tight. We have to be careful when we build very tight homes, we also include controlled ventilation.
"Overall, we saw better building practice and good attention to detail, which is leading to positive results.
"Our message for the building industry is that constructing a well-sealed home is neither new, nor daunting. It's manageable, and plenty of builders are already achieving great results for homeowners."