Air Tightness and Smoke Infiltration

The Situation

Living in the harsh climate of Australia, we are vulnerable to the many wiles of nature. Flash flooding, hurricanes, even earthquakes and of course, bushfires. Two years ago, across late 2019 and early 2020, we saw the worst bushfire season South East Australia has ever experienced, now colloquially known as “Black Summer”. Not just Black Saturday, Black Summer. This fire season extended from July 2019, to March 2020, and reached its peak in December / January.

  • 18.6 million hectares of land was scorched
  • Nearly 6,000 buildings were destroyed
  • At least 34 people died.

The immediate impacts of the fires were devastating for thousands of Australians, however the impacts of the smoke are long lasting and far reaching. By early January, 2020 the smoke had moved across the ocean and turned glaciers in New Zealand brown (below left) and smoke particles had even reached Argentia (below right).


Health Impacts of Smoke Inhalation

Common side effects of smoke exposure are::

  • Shortness of breath
  • Wheezing and coughing
  • Burning eyes
  • Running nose
  • Chest tightness
  • Chest pain
  • Dizziness
  • Psychological distress

Although the above symptoms present with differing levels of severity, even minor discomfort associated with smoke exposure is unpleasant and when our buildings are so leaky, in the case of fire there’s nowhere we can go to get away from the smoke. Further to this, carbon monoxide particles can linger in the air for up to a month. Particles smaller than 2.5 micrometres (PM2.5) can penetrate our lungs and bloodstream making them extremely dangerous, attaching themselves to our red blood cells and essentially suffocating us. Inhalation of these particles is the primary reason people die from smoke inhalation, particularly the vulnerable or elderly.

The Situation

As members of society, we want to protect our community and our families from the devastating impacts of bushfires. When we think about what we can do to help, our immediate surroundings are the first thing we think about. Clearing debris from our properties, installing sprinkler systems on our roofs, having a bushfire plan to get out quickly when necessary. One thing that doesn’t get properly considered is the air tightness of our homes. In AS3959:2018 Construction of buildings in bushfire-prone areas (AS3959) there is a strong focus on resistance to ember attack at every BAL level between 12.5 to FZ (Flame Zone). This is incredibly important as many fires start due to embers and not the fire front itself. But another important consideration is smoke. Smoke travels thousands of kilometres from the fire front and affects people and buildings on the other side of the world. There is not much that can be done about the smoke in the atmosphere, so to try to escape that smoke we go inside our houses. Inside our buildings. Only to find there’s smoke in there too. The only way smoke is kept out of buildings is to seal them up tight. To get rid of the gaps and cracks that shouldn’t be there, however building sealing is only loosely mentioned IN AS3959 in the General requirements at Clause 3.6.2 Gaps to door and window openings:


“Gaps between doors including jambs, heads or sills (thresholds) shall be protected using draught seals and excluders or the like”


“Windows conformant with AS 2047 will satisfy the requirements for gap protection. Screens fitted to window openings shall have a maximum aperture of 2.0 mm and these shall be tight fitting to the frames”

What I’m getting at is that building sealing and air tightness is barely mentioned, is very loosely defined and is only for new buildings. What about the older buildings, built before even the current, loose standards? To the left is a snapshot of a Facebook status update from a friend of mine from Canberra during Black Summer that says it all.

This house was built in the early 1980s and is representative of many houses across the entire bushfire front and surroundings. Her house was so poorly sealed that she and her husband were having to tape their windows and doors to prevent smoke ingress.


“It’s red brick, with wind out windows and ducted heating through the ceiling. It was so hard to keep the smoke out…. Even with every window shut and towels pushed up against every door it found ways to get in. We had to run our split system 24/7 just to try and filter some of it out. “

Natalie Graham, Canberra, ACT


They ended up with a fine layer of ash over everything within their house and had a lengthy clean up process afterwards.


[We had] “…a fine layer on everything – we had to wipe down all of our blinds and wash curtains that we had to have closed to have as a barrier against the smoke”

Natalie Graham, Canberra, ACT


You could say they were lucky to not have been directly affected by the flames, but within that luck they were also negatively impacted by the quality of their home and to add to the stress, at the time they had a young baby and were very concerned about protecting his health.


It was pretty scary with *******, just because **** and I could wear masks but he was only 6 months old so couldn’t … we almost left to come to one of the hotels because of him….. I can tell you breathing in that much smoke makes you feel sick all day

Natalie Graham, Canberra, ACT


Natalie and her husband were not at the fire front. They lived about 2.5 hours drive away, or about 250kms. As stated in the introduction to this piece, smoke from Black Summer travelled all the way to South America, some 11,150km. It turned the glaciers in New Zealand brown. Smoke isn’t just an issue in the local area of the fire and it gets into our homes. Into our places of safety and protection.

“Staying indoors might provide some protection against bushfire smoke, but this depends on building quality and ventilation. In general, most residential houses are not equipped with air purifiers or air conditioning systems with high-efficiency filters. Hence, outdoor pollutants can still penetrate into houses, if they are in bad conditions or equipped with air conditioning systems without air filters. Therefore, indoor and outdoor concentrations of fine particles are often very close.”

Below is an extract from the Canberra Times during the bushfires from Canberra resident Jonathan Milford stating exactly that:

The current AS3959 standard does not require any form of air tightness testing to ensure smoke infiltration is kept to a minimum and that air is filtered.

Below are the results of some research carried out by the CSIRO in 2015 on the current housing stock in Australia; currently the only official air tightness data released in Australia. Around 130 houses were blower door tested. They were no more than 4 years old and the results varied drastically across the country, from 3ACH to up around 40ACH.

The average Australian household experiences an air tightness score of 15.4 ACH @ 50Pa. To put that into perspective, the Passive House standard requires 0.6ACH so the current Australian standard is nearly 26 times as leaky as Passive House and the air coming in is unfiltered.

What Can Be Done

As explored in this article, embers and smoke affect homes far from the fire front and we certainly can’t stop the spread, however we can reduce the health impacts of smoke infiltration into private dwellings fairly simply. In the fire zone to start with, and expand from there. It starts with education.

  • Correct education of the general public so they understand the problem and how to reduce their exposure and what the retrofit options are
  • Correct education of trades, builders and architects so that the buildings are built correctly from the outset

And continues with a change in the regulations to ensure that, on top of the combustibility measures, sufficient building sealing is also taken into consideration:

  • A blower door test is completed on every house in a bushfire zone aiming for 3ACH or below
  • Mechanical ventilation is installed in every house in a bush fire zone

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