How to lower your BAL rating
Of the four things that set a BAL under Method 1, location fixes the fire danger index and what's growing fixes the vegetation class. A site plan can change distance and slope: where the building goes decides how far it is from the vegetation, and whether that vegetation sits on ground falling away from the building or rising towards it.
Distance: the main lever
The closer the vegetation, the higher the BAL. Moving the building further from a patch of vegetation lowers that patch's level once the building passes the distance where the next lower level starts. Because the building takes the highest level from any patch, what matters is the patch that sets the BAL: moving away from a patch that doesn't set it changes nothing.
Slope: where the building sits
Vegetation on ground falling away from the building is more dangerous than vegetation on flat or rising ground, because fire runs faster uphill. The slope of the ground under the vegetation can't usually be changed, but the building's position decides which way the ground runs between them. A building sited so that the nearest vegetation is upslope or on flat ground can get a lower level than one sited above a slope covered in the same vegetation.
A worked example
After you press Complete, BAL Buddy shows the indicative BAL and, for the patch that sets it, how far the building would need to move away from that patch to reach the next lower level. The figure is rounded up to the next 0.1 m, so moving that far always gets there.
Say the result is BAL-29, set by a patch of woodland on ground falling away from the building, and BAL Buddy says to move the building 4.3 m further from the woodland for BAL-19. (These figures are made up, to show how the result reads.) Three things to check before relying on that move:
- Other patches. If another patch also gives BAL-29, moving away from the woodland alone won't lower the result. BAL Buddy says what the building's BAL would then be.
- The new position. Moving the building changes the distance to every patch, and can bring it closer to another one. Redraw the building in its new place and run it again to see the new result.
- The slope. In a new position the ground under the vegetation may slope differently relative to the building. A rerun works the slope out again.
Changes on the same site, within 50 m of where the building was, are recalculated free for 30 days, so trying a few positions there doesn't use more runs.
The vegetation itself
A site's BAL depends on the vegetation around the building, so clearing, regrowth, new planting or a change in how land is managed can change it, in either direction. Whether vegetation can be removed is a separate question, and an indicative result doesn't answer it.
Checking the answer
An indicative result helps you compare positions early. Your building surveyor or council decides which BAL applies, usually on a BAL assessment by a suitably qualified person, and that assessment should be the basis for design decisions. How a BAL is worked out explains the inputs, and BAL levels explained what each level means.
BAL Buddy gives an indicative Bushfire Attack Level (BAL) only. It isn't a determination under any Act, and no council or building surveyor has to accept it. For a BAL you can rely on, use an accredited bushfire practitioner.
Questions people ask
Does moving the building always lower the BAL?
No. It lowers it only if the building moves far enough from the patch that sets the BAL, and no other patch gives the same level or higher at the new position.
Why is the move figure rounded up?
So that moving the building that far always reaches the next lower level. Rounding down could leave it just short.
Can I change the slope?
Not usually the slope of the land under the vegetation. Where the building sits decides whether that vegetation is on ground falling away from it or rising towards it.
Does trying another position cost another run?
Not within 30 days, while the building stays within 50 m of where it was.