Designing to survive devastating bushfires has three directions: designing the bush, designing houses, and designing protection.

Designing the bush

Bush politicians (mostly Nationals and One Nation) often say the problem is the bush itself: too much, too close, in the wrong place, and not enough hazard reduction. This is an attempt to ‘redesign’ the bush to make it safer (and defy climate change).

They want to ‘design the bush’ to manage the risk by advocating:

Hazard reduction: smaller window of opportunity, AND ineffective in severe fire, ineffective over time;
Increased logging: seen as a way to reduce the problem but can actually make bushfires worse;
Bush clearing, does assist but is not “living in the bush”, a tree change with no trees is pointless;
Removing green tape: code for easier legislation to assist the above (including privatising the forests).

Some of these processes may have worked in the past but are now quite ineffective at protecting lives and houses in severe fires. Better design practices for the bush would be:

Looking to indigenous practices outlined in recent research;
Redesigning building surrounds: a mix of better bush clearing and fire-resistant landscapes;
Both approaches will help to create a ‘defendable perimeter’.

Designing houses

Considerable research has been done in the last 25 years on the ‘safe design’ of buildings in bushfires by the CSIRO and the ABCB (Australian Building Codes Board, in charge of the BCA Building Code of Australia).

The Codes and Advice:

Designing to the BAL (Bushfire Attack Level); determines likely risk, in 5 levels from ‘Low’ to ‘Flame Zone’.
Have comprehensive requirements for each of the BAL’s for all parts of a house, including infrastructure.
Can be complicated, contrary to ‘current best practice', and 20-30% more expensive.
Can make houses less pleasant to live in: less sunlight, less cross ventilation, less shade, etc

BUT a building built to the ‘Flame Zone’ standard may still burn down in severe bushfires, even if the ember attack is resisted. The radiant heat of fires at 800-1,000°C+ will melt many materials and explode covered glazing.

Codes only apply to new buildings and won’t improve the overwhelming number of existing houses. Since we add only about 2% new buildings to our building stock every year, even if we could immediately change the construction of all our house designs to the highest standards, it would take 35 years for 50% of buildings to meet that best-practice standard.

Designing protection

An alternative approach for all buildings, existing and new, is to design bushfire protection to protect both lives (in a shelter) and buildings (with sprinklers).

Shelters

The safest protection for humans at a house site is a ‘private bushfire shelter’. After exhaustive research these shelters, sometimes referred to as ‘bunkers’, were codified by the ABCB in 2014. Compliant designs most often have concrete floors, walls and roofs, are partially or wholly earth protected (underground or in an embankment) and are usually fitted with compressed air in tanks to keep the smoke at bay.

Whilst shelters offer the best chance of survival for those who choose to stay and defend, the Codes warn they are only intended as a refuge from fire intensity at its height and are not a foolproof or certain solution.

Sprinklers

One very effective protection against bushfires, for all buildings old or new, is external wetting sprinklers. In the same way that fire suppression inside buildings is by automated sprinklers (increasingly mandatory across a wider range of buildings), they can be used to prevent or suppress fire on the outside.

Sprinklers are mounted to protect key areas such as ridges, eaves, gutters, and windows and door glazing and may be automatically operated or manually controlled when the fire approaches.

There is an Australian Standard, AS 5414-2012 (Bushfire water spray systems) (originally developed in 2012). The standard governs the general design, installation, and maintenance of exterior water spray and sprinkler systems meant to defend buildings against ember attack and limited radiant heat exposure (up to BAL 19).

AS 5414-2012 has existed for years, historically operating as an auxiliary or performance-based design standard rather than being universally mandated or fully integrated into the core AS 3959 building construction rules. Its current status is “pending revisions”, with a public comment draft circulating through industry groups. The ongoing revision aims to update requirements, water demand calculations, and wider adoption.

It has been criticised over technical issues; for not addressing all BAL levels; and that like all Australian Standards it should be free, rather than costing $155. Nevertheless, a niche industry has developed solutions using the standards and adapting the technology to differing house types and forms.

The system has costs: the sprinklers themselves can be $10,000-15,000, the pumps and controls another $5,000, and the water tanks are large in size and may run to tens of thousands. The system needs between 400 and 1,000 litres/min; to work for an hour while a fire rages, the system would require up to 40-60,000 litres; that’s a water tank of 5-6 metres in diameter and 2 metres tall. Collecting all that water and keeping it clean and available is a considerable task given the drought.

The system is ideal for protecting existing buildings, particularly heritage-listed or venerated traditional buildings in towns and villages. As bad as the destruction of individual buildings was in Cobargo, NSW, during the Black Summer Bushfires (December 2019), it is all the more distressing that, as a suite of buildings, they made an ensemble that provided the essence of the town.

Governments should consider subsidies or loans for both shelters and sprinklers, and this should be part of any future bushfire plan or a protection authority. Owners should be able to protect every building they want, with or without government subsidies or loans.

We need better bushfire planning policies. Better tree management based on Indigenous principles and better building codes for all new buildings for more severe fires, but more importantly, our focus must be on people in existing buildings. Whether it is at the edge of towns, in villages, or deep in the bush, we need to develop a way to store water in a dry, drought-ridden landscape and be able to ‘drown the house’ when the fire comes.

Note: The author and others will discuss these issues in a seminar at this year’s Sustainability Summit.

Cross-Sections are Friday musings from Tone Wheeler, formerly of Tone on Tuesday. Amateurs draw plans; professionals draw sections – never at cross purposes.

Tone Wheeler

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