The second required element addressed in a Bushfire Management Plan (BMP) is siting, which is described in the bushfire protection criteria in the guidelines to planning in bushfire prone region. The intent of this element in the Bushfire Management Plan (BMP) is to ensure that the siting and design of the development poses the least bushfire risk possible. One of the key factors in declaring a Bushfire Attack Level (BAL) rating for a site is the distance from classified vegetation. As per AS3959, Table 2.4.3 (for Western Australia) gives you separation distance (measured perpendicular from the elevation of the building) from classified vegetation and the Bushfire Attack Level (BAL) rating your development is as a result of that. Imagine a scenario where you propose a development on a site that has classified unmanaged vegetation on it, any building you propose will be at a separation distance of 0 m from classified vegetation making your Bushfire Attack Level (BAL) rating a BAL-Flame Zone (FZ). Such a high rating will most probably not be granted developmental approval as it poses a high bushfire risk to both people, property and infrastructure. Therefore, the application is not supported unless accompanied with a Bushfire Management Plan (BMP) which is to meet the four elements of the bushfire prone criteria particularly Element 2; Siting.
Siting essentially means the site development and management of vegetation on the site itself to reduce the bushfire risk as much as possible. This is carried out by forming an “asset protection zone” around the proposed building within which all vegetation is managed in a low fuel condition. An asset protection zone (APZ) is of a preferred width of 20 m at least. So in the scenario we previously imagined, if the site had an asset protection zone of 20 m around the building, then the Bushfire Attack Level (BAL) rating of BAL-Flame Zone (FZ) may drop to BAL-19 as the separation distance is now 20 m instead of 0 m.
Now imagine a scenario where you are proposing a subdivision and your property boundary is at a separation distance of 14 m from a Group B Woodland, the Bushfire Attack Level (BAL) rating for your development would be BAL-40 (As per AS3959, Table 2.4.3). Again, a very high rating that is unlikely to be approved. In this case, it is advisable to propose a building envelope during the developmental process so an asset protection zone can be proposed around the building envelope to increase your separation distance from classified vegetation. The Bushfire Management Plan (BMP) will clearly detail the building envelope. Care must be taken however as you cannot build outside a building envelope already approved by the WAPC.
For larger subdivisions, the Bushfire Management Plan (BMP) can also propose a hazard separation zone (HSZ) which like an asset protection zone (APZ), proposes the management of vegetation, but can extend up till 80 m after the 20 m asset protection zone. This in turn can account for a Bushfire Attack Level (BAL) rating of BAL-LOW as the separation distance is now a 100 m.
An important factor to note is that both an asset protection zone (APZ) and a hazard separation zone (HSZ) can only be proposed as part of a Bushfire Management Plan (BMP) and only within the boundaries of the property of the proponent of the Bushfire Management Plan (BMP). Therefore element 1; Location must be optimised first to achieve a maximum separation distance from classified vegetation through Element 2; Siting.
Due to constantly evolving legislation the information provided within this blog may no longer be valid. The advice given on this site is general in nature and does not take into account your specific circumstances. Please email one of our building surveyors to check what is right for you