Can you lower your BAL rating?

A BAL rating is not something an assessor can lower. It is a measurement of the site as it stands, calculated from three inputs: vegetation, distance and slope. What people are really asking is whether changing the site or the building position would produce a different measurement. Sometimes it would. This article explains the inputs so you can have that conversation with your designer or council, and be realistic about what is and is not possible.

The three levers

1. Distance from vegetation

The rating is calculated from the distance between the building and the nearest classified vegetation in each direction. A house positioned further from a forest edge will measure lower for that aspect than one closer to it. On a new build, building position is a design decision for you and your designer to make before plans are finalised.

2. Vegetation management

Under AS 3959, some vegetation can be excluded from the assessment if it is managed to a low-threat state. Maintained lawns, gardens, orchards and cleared areas kept to a low fuel load are treated differently to unmanaged bushland. Whether and how to manage vegetation is a decision for the landowner, made with council. Two important caveats:

• Native vegetation clearance in South Australia is regulated. Before removing anything beyond routine garden maintenance, check with your council and the Native Vegetation Council. Some clearing is permitted for bushfire protection; some is not. We do not advise on what to clear.
• The assessment reflects the vegetation as it is on the day. A promise to clear later does not lower the rating. Do the work first, then assess.

3. Slope

Slope cannot be changed, but it affects the result. A house downslope of forest is exposed to longer flame lengths than one on flat ground at the same distance, so different positions on the same block can measure differently.

What does not work

• Vegetation on land you do not own. If the threat is on a neighbour's property or a road reserve, it counts regardless of what you do on your side.
• Fences, walls and screens. These are not recognised as reducing radiant heat under the standard.
• Getting a second assessment hoping for a different number. The method is prescriptive. Two competent assessors looking at the same site should arrive at the same rating.

The practical approach on a new build

1. Get the assessment done early, before the plans are locked.
2. Ask for the rating by aspect. Often only one side of the house is driving the highest number.
3. Take that to your designer. They can tell you whether a different footprint is workable.
4. If the site or building position changes, the assessment needs to be redone. Build to the final rating.

Sometimes the rating stays where it is and you build to it. That is fine. The point is to have the information before the cost is locked in.