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When is a bunker not a bunker? Say hello to fire-resilient homes



The Bushfire Building Council of Australia (BBCA) on Thursday released free architectural drawings, specifications and handbooks that will make it easier, cheaper and faster to build sustainable houses resilient to bushfires, floods, storms, heatwaves and cyclones.

During an emergency, most people only have time to grab their dearest possessions, their pets and their passport, before running out the door. 

But what if this wasn’t the case? What if you could lock your door and head off, safe in the knowledge that your home would likely be fine when you returned? 

New schematic designs from the Bushfire Building Council of Australia (BBCA) aim to counteract this harsh reality, with the group releasing plans for homes that are resilient in a range of disasters including bushfire and flooding. 

The new home ideas are backed by insurers and government, and promise an affordable and fast delivery.

According to the BBCA, 2.5 million Australians live in high bushfire risk regions – and 90 per cent of buildings in high bushfire risk areas are not resilient, meaning that $1 trillion worth of property is at risk. 

The FORTIS project offers architectural drawings and specifications that were created through collaboration with experts in fires, cyclones and floods, as well as local community members. 

FORTIS House BBCAFORTIS House designs – the fire and flood proof home from the Bushfire Building Council of Australia. Image: BBCA

“FORTIS House will save time and money, fast-track the building process and help people create an affordable, sustainable, adaptable and highly resilient house,” said BBCA chief executive officer Kate Cotter.

A whopping 97 per cent of disaster funding is spent on recovery actions and only three per cent on mitigation or resilience measures, according to the Productivity Commission.

The design

During a bushfire, “flames can sustain temperatures upwards of 1200 degrees… The radiant energy can be upwards of 100 KW per square metre. That’s really, really hot,” CSIRO bushfire behaviour expert Dr Andrew Sullivan told The Fifth Estate in a recent interview.

According to Ms Cotter these conditions call for a “self-defending” home, meaning that the resident can close up the house and leave their property safely, expecting to return to their home in one piece. 

Fire resilience is achieved mainly through robust external steel screens that provide protection from embers and radiant heat, wind and water. Windows are set back internally to limit heat transfer, but to ensure that occupants can still maintain good visibility. 

It is important that the design does not feel like a bunker, Ms Cotter told The Fifth Estate, so protective design features were made for everyday use. Sliding steel screens are not just for an emergency. Shutters and screens can be used for shade everyday, and screens can be used for insect protection and airflow. Different door systems mean that people won’t be trapped in an emergency.

“It needs to behave like a bunker but still be able to be used every day.”

The Fortis home takes around 12 weeks to construct and costs upwards of $300,000 to build. Builders and prefab manufacturers were involved from the start to ensure that the design could be fast and affordable. The fast construction time was a critical requirement for the many people in bushfire-prone areas that haven’t been able to access emergency housing.

FORTIS House BBCAFORTIS House designs – the fire and flood proof home from the Bushfire Building Council of Australia. Image: BBCA

Large windows in the homes deliver natural light and connection to nature, but windows are a point of high heat transfer – and they are also more likely to shatter at high temperatures. That’s why the home has external steel screens for protection.

According to fire expert Dr Andrew Sullivan: “Radiant heat impinging upon a building means that glass and window frames will start to fail at about 12-15 KW per square metre. Usually, your fire must be some distance away from the house to be able to withstand that”.

Finally, landscaping guidelines ensure the fire is kept away and there is a safe evacuation point.

“The vegetation around the house plays a role in how the house will respond to the arrival of the bushfire,” explained Dr Sullivan. 

“If you can reduce the amount of available fuel, you decrease the chance of fire reaching the property.” 

FORTIS is 100 per cent electric, self-sufficient with solar power and energy efficient design. The guidelines stipulate recyclable materials. The buildings are built to last and withstand extreme weather and disasters, reducing landfill and rebuilding environmental impacts.

The process

Following the bushfires of 2019-2020, the organisation received many enquiries from homeowners wanting to know how to future-proof their homes from fire. It has been a two year process to bring the plan to fruition. 

The designs were made in collaboration with the community at Shoalhaven on the NSW South Coast who had lost their homes, and with the help of engineers, architects and disaster professionals to ensure that the design measured up. 

The Shoalhaven area has on average 600 bushfires a year according to the NSW Rural Fire Service, of which an average of 20 fires can be considered to be major fires. 

FORTIS House BBCABBCA chief executive officer Kate Cotter. Image: BBCA

“We wanted technical solutions to engineer resilience into what the community was asking for. That was the challenging part,” Ms Cotter said.

She said there were “challenges on how to bring different disaster types together in the design”. 

For areas that are both flood-prone and fire-risk, the specific internal features will be different. For example, to mitigate flood inundation the design specifies elimination of wall cavities below the water line. And the home is raised above the water line.

“There’s some tradeoffs you have to make.”

Build location

Having a fire resilient design isn’t the only important thing you can do to minimise the risk of losing your home. You should also consider the location when building.

The CSIRO recently unveiled a new $2.1 million bushfire behaviour research facility located at CSIRO Black Mountain Canberra, which will house its Pyrotron and Vertical Wind Tunnel, two instruments designed to aid scientists in researching bushfires in a controlled environment. 

CSIRO bushfire behaviour expert Dr Andrew Sullivan told The Fifth Estate that there are three factors that influence fire behaviour, called the “fire behaviour triangle”: topography, weather, and fuel. 

On the first factor, building on a slope increases the consequences of a fire, because fire accelerates exponentially when moving up or down a hill. 

CSIRO_Pyrotron Dr Andrew Sullivan Dr Andrew Sullivan overseeing the CSIRO Pyrotron experiment equipment. Image: CSIRO

The speed will double the “flat ground rate of spread” for every 10 degrees of slope, he explained. So, if your home is on a 20 degree slope, the fire will be moving at 20 km an hour – that’s twice as fast as the average person can run.

The other factor that you have control over is the fuel, or vegetation around your home. 

“If you can reduce the amount of available fuel, you decrease the chance of fire reaching the property. 

“One thing people aren’t aware of is that one kilogram of dry vegetation has the equivalent energy to power a lightbulb for 24 hours – but that energy can be used up by the fire in around 10-15 seconds.”

In an emergency situation, expert advice is to lock up and evacuate – even if you have a fire resilient home. 

But if something goes wrong and the evacuation route is cut off or it is too late to leave the property, Ms Cotter said that the Fortis home is “a place of last resort”.

“There’s resilience built in so that you can survive”. 

“It’s always better to be safe than sorry,” Dr Sullivan said.