20 Jan Blog

Building in bushfire prone areas

More than 3,000 properties were destroyed in the 2019-2020 bushfire season, and 33 people have lost their lives. There is hope that the unique weather patterns that created the perfect circumstances for the devastating bushfire season will not be seen again this year, but we cannot rely on the weather alone.

This article looks at some of the strategies that can be employed to make houses more fire resilient.

Apart from the emotional turmoil of losing a home, a property is usually our most important investment. 

While there will never be a guarantee that your house will survive a blaze under severe circumstances, there are certain strategies you can follow to improve the odds.

Please note: The State Rural Fire Service and other emergency services put out regular communication regarding fire updates during bushfire incidents and should be seen as the first point of information under all circumstances. Strategies to fire-proof a property may minimise the damage, but we do not advise using the home as shelter when emergency services indicate that leaving the area is advisable. The safest option is always to leave early! 

Fire resistance starts with design

To give a building a fighting chance of surviving a bushfire, fire resistant strategies need to be implemented from the design stage. Architects and bushfire experts agree that it is time to rethink how we design buildings in bushfire prone areas.

“Australians need to (re)think beyond the paradigm of the timber hideaway in the bush and realise that being able to inhabit such sites is an extraordinary privilege - and with that privilege comes the onus of building bushfire resilient homes - rather than modifying that landscape to suit their preconceived and outdated ideas,” said Dr. Ian Weir, a researcher at Queensland University of Technology who studies bushfire responsive architecture. (Read the full article here.)

The Australian Institute of Architects established a dedicated bushfire response website where a number of its Acumen practice notes relating to post-fire design is freely available.

“This is not a short-term crisis, and we need the support of the architectural profession to support us as we face this crisis together. When the fires clear, we will need to not only replace what has been lost, but build back better,” the Institute stated on the website during the 2019-2020 bushfire crisis.

Passive house design

Passive house design is gaining popularity in Australia due to its focus on sustainability and energy efficiency.

It relies on the adoption of a few key design principles to enable the creation of energy efficient buildings with healthy, dry indoor spaces that require little or no heating or cooling. Read more about it in our blog The 5 principles of passive house design.

A big win of this design trend is that many of the strategies employed in this type of sustainable construction can also help to make a property more fire resilient. This includes the use of triple-glazed windows and an airtight building envelope, which for instance prevents toxic gases and smoke from entering the building.

Knauf Australia supplied plasterboard to Sapphire HouseAustralia’s first passive house built to the highest bushfire rating (BAL-FZ). Read more about bushfire ratings (BAL) below.

Standards and codes

Over the last 25 years Australian building codes and standards have become considerably more comprehensive to include strategies to make buildings more fire resilient.

The codes include performance standards and appropriate materials to resist bushfire attack. 

The current standards related to bushfire issues are:

National building requirements for residences in bushfire prone areas were improved after the 2009 “Black Saturday” bushfires in Victoria, in which 173 people died and more than 2,000 homes were destroyed.

According to an article in published on The Conversation in January 2020, more can possible be done to make homes more fireproof, but that doesn’t necessarily mean Australia’s building regulations need reforming to ensure homes are made more fireproof.

"Appropriate building codes are about weighing costs and benefits. Only analysing the reasons buildings were destroyed will tell us if more needs to be done," the article states.

Fire Resistance Levels (FRL)

The Building Code of Australia (BCA) includes requirements for walls and ceilings to help ensure the safety of occupants in the event of a fire, regardless of whether the structure is built in a bushfire prone area or not.

The code defines the Fire Resistance Level (FRL) of a structure in terms of three criteria: structural adequacy, integrity and insulation.

  • Structural adequacy: The ability of a structure to maintain its stability and loadbearing capacity in the event of a fire
  • Integrity: The ability of a structure to resist the passage of flame and hot gases during a fire
  • Insulation: The ability to maintain a temperature over the whole of the unexposed surface below that specified by AS 1530.4

If the FRL requirement for a wall is 90/60/30 it means that the wall will maintain its structural adequacy for 90 minutes, resist the passage of flame and hot gases for 60 minutes and maintain its temperature (below set limits) on the unexposed side for 30 minutes.

A dash in FRL means that there is no requirement for that criterion. For example a wall that has an FRL of -/90/90 means that there is no structural adequacy requirement for that wall system (e.g. non-load bearing walls).

Read more about fire ratings in our blog How to select a fire rated wall or ceiling.

Bushfire Attack Level (BAL)

In addition to the provisions of the BCA, the Australian Standard for Building in Bushfire Prone Areas (AS3959) provides further requirements for residential dwellings built in areas that pose a high risk of bushfires.

The AS3959 divides bushfire prone areas into six bushfire attack levels (BAL), based on the severity of the building’s potential exposure to ember attack, radiant heat and direct flame contact in the event of an uncontrolled bushfire. BAL ratings are measured in increments of radiant heat expressed as kW/m2.

The most severe bushfire attack level is described in the standard as BAL-FZ and is primarily concerned with protection from flame contact together with ember attack and radiant heat of more than 40 kW/m2.

All new residential homes built in a bushfire prone area must undergo a BAL assessment as part of the application for a building permit.

The six BALs are:

  • BAL-LOW - very low risk
  • BAL-12.5 - low risk
  • BAL-19 - moderate risk
  • BAL-29 - high risk
  • BAL-40 - very high risk
  • BAL-FZ - extreme risk (Flame Zone)
    BALs

AS 3959 explains how the BAL for a property is determined and provides the construction requirements for each level of BAL, including for floors, roofs, external walls and windows, verandahs and carports.

All new homes built in a Bushfire Prone Areas must be built to a minimum of BAL- 12.5.

BALs may change due to environmental factors, such as when nearby cleared areas become forested.

At Knauf Australia we therefore recommend always building to BAL-FZ requirements because any solution that satisfies the requirements of BAL-FZ will also work for a lower BAL.

Also read A guide to accessing your property’s Bushfire Attack Level (BAL).

Existing buildings

While codes, standards and improved design strategies can go a long way to improve the fire resilience of new structures, it remains extremely difficult to protect older structures.

The NSW Rural Fire Service provides a few basic maintenance tips to prepare a property for a bushfire, including cleaning gutters of twigs and leaves, attaching a fire sprinkler system to the gutters and cutting back trees and shrubs overhanging the buildings.

Also refer to bushfire architect Dr. Douglas Brown’s recent blog, 12 simple ways you can reduce bushfire risk to older homes.

If you are interested in a CPD session on Fire Rated Internal Walls, please fill out this form and we will contact you.

For more information on Knauf’s fire resistant and BAL compliant solutions, contact our technical services team on 1 300 724 505.