When the Heats on It Gets Complex


Summer, heat and bushfires go together. And when they arrive they’re either bad or they’re catastrophic.

As we enter into bushfire season yet again we must not lose sight of what happened this time last year. We must not become complacent and risk life and property unnecessarily again.

Whilst my expertise is not in putting out bushfires or determining what the weather will do, my expertise allows me to look at the properties that we build and the design codes that are legislated to protect us. My expertise also enables me to look at things with common sense developed over 40 years in my industry.

If it can go wrong it will is a great way of looking at designing against disastrous events. Bushfires, cyclones and floods are classic examples of this. But today we are focusing on bushfires.

In Australia we have BAL ratings for designing in bushfire prone areas. BAL means Bushfire Attack Level and provides a measure for the different designs required for various levels of BAL. Australian Standard 3959 titled “Construction of buildings in bushfire-prone areas” is the major document we use to design for bushfire.

The major issues that affect the BAL rating for a house site are the type of vegetation surrounding the proposed house, the distance from the proposed house to any classified types of vegetation, and the slope of the land between the proposed house and the classified type of vegetation. Sound complex? Believe me, this is the simplified version.

Once a BAL rating has been determined the designers are able to select the types of construction materials and methods of construction. Whilst the Australian Standard is quite comprehensive, the designer must also comply with assorted other Australian Standards and the National Construction Code (formerly the Building Code of Australia).

Now we really are talking about something very complex. And this is where I see things getting lost in translation. When the designers try to design in everything that all these various Standards and Codes require, combined with a client’s functional design needs and budget constraints, there are bound to be problems.

Bushfire resistant construction is very expensive. The higher the BAL rating the more expensive it becomes and the less functional a design can be if budget is a constraint; and let’s face it, very few people have an unlimited budget. Yes, this means problems.

When you look at a typically designed house in a BAL-LOW location there are no specific requirements other than complying with the NCC and various other Australian Standards. This means no flyscreens are required and various gaps and penetrations around the building have no specific limits. In BAL-FZ (meaning flame zone) the flyscreens must be fire resistant screening material with an aperture size of no more than 2mm, to prevent ember attack, and any gaps and penetrations must have a maximum size of 3mm to reduce the penetration of radiant heat. Just writing this makes me feel how complex this actually is.

And now let’s add the human factor to the construction and supervision activities. Have you ever seen a house with gaps around and under doors of only 3mm maximum? It’s almost impossible to make this happen, and that’s just the doors. Every junction of one material to another, one wall to a window or to the eaves, roof tiles, flashings, cappings, absolutely everything has gaps. Trying to prevent gaps larger than 3mm and covering openings with 2mm mesh is difficult and time consuming. There goes the budget yet again.

Now let’s look back on the catastrophic bushfires from last summer and think about whether the above BAL-FZ construction requirements would have made any difference. The fire storms that were being reported and shared around the world via the internet were more ferocious than BAL-FZ would have been able to protect. So what do we do? How do we protect life and property? Do we forbid people from building a home in the bush? Do we clear 100m all around a house (that’s more than 3 hectares of land for one house)? If we are truly committed to saving lives then we must not only be concerned with the occupants of the house but also the emergency services crews who should not be required to put their lives at risk to save others from inappropriately designed homes. It’s complex!