Building with timber in a bushfire zone

Building with timber in a bushfire zone

Jul 14, 2020

 

Following the recent bushfires that ravaged much of the country and destroyed more than 2,779 homes, you’d be forgiven for thinking the only way to live safely near the bush is in a concrete bunker. But by following the relevant design principles and regulations, you can still build a beautiful and bushfire-compliant home using timber. Here’s how...

Know your bushfire risk

Bushfires have always been a part of the Australian landscape, and in response there now exists a set of risk-averse guidelines under Australian Standard AS 3959-2018 Construction of Buildings in Bushfire-prone Areas. These specify the way in which homes should be built and the types of materials they should be constructed with to minimise their bushfire vulnerability.

Every new home or renovation in a bushfire-prone area must undergo a Bushfire Attack Level (BAL) assessment to attain a building permit. Your home’s BAL rating will be based on the local climate, slope of the land and its proximity to vegetation. There are six levels, ranging from BAL-LOW (very low risk) to BAL-40 (very high) and even BAL-FZ (flame zone; extreme risk), each with their own set of requirements regarding the construction and materiality of your home.

People living in suburbs or built-up areas will most likely fall under the BAL-LOW category, which means there is such a low level of risk from bushfire that these homes can use any standard construction materials and methods they like, including timber. The next level up, BAL-12.5, is deemed to have a low risk of ember attack, and as such, requires the use of fire-resistant timber types for external doors, windows, cladding and decks. At the other end of the scale, properties classed as BAL-FZ are usually surrounded by bush and have a high predicted risk of direct exposure to flames from a fire front or ember attack. Even so, specifications allow the use of some durable timber species and suitably treated timbers for enclosed subfloor spaces, internal framing and internal joinery.

Safe ways to build with timber

Timber is an ideal choice in a bushland setting. It’s a renewable resource, offers visual and textural appeal and is extremely durable. You can stain it, paint it or leave it to weather naturally to blend in with its setting. Thankfully, Australia has several high-density timbers that possess an inherent natural bushfire resistance, known as bushfire-resisting timbers (BRTs). These include blackbutt, merbau, red ironbark, river red gum, silvertop ash, spotted gum and turpentine, all of which are permitted for some uses in bushfire-prone areas up to BAL-29.

The building standards place no restrictions on framing materials, given it’s not generally exposed to direct ember attack or flame contact, so regardless of your rating, you can still work with soft or hardwood timber frames. Likewise, there are no limitations regarding internal joinery, such as doors, wall linings, ceiling linings, staircases and floorboards.

You’ll face more restrictions around the outside of your home, but in a range of situations, appropriately treated timber products and high-density Australian hardwoods are still suitable, when applied in a way that minimises fire danger.

A holistic approach to bushfire safety

It can be a complicated process building in a bushfire-prone zone, but calling in the professionals will alleviate a lot of stress and confusion. Engage an architect to help with your building design, and work with your builder and architect when selecting construction materials to ensure they meet with Australian Standards.

And remember, using the recommended materials alone can’t guarantee your home’s survival should a fire come through. A combination of good design, careful construction and sensible maintenance are essential to producing a house that can withstand the threat of a bushfire. Installing a water tank with fire brigade fittings or roof sprinklers may be required, and most importantly you should have an up-to-date bushfire plan and be well-versed in the correct procedures for protecting yourself and your property.

Photos:

Port Sorrell Community, Recreation and Performing Arts Centre – ARTAS Architects

Davenport Wilson House – Shane Thompson Architects