This updates the previous Interim Practice Note 2009-42 issued August 2009
Reference to the BCA in this Practice Note means Volume One and Volume Two of the National Construction Code Series.
Building in bushfire areas requires careful planning, siting and design. Class 1, 2 or 3 and associated Class 10a buildings must be designed and constructed to reduce the risk of ignition from a bushfire while the fire front passes. The building requirements are set out in the Building Code of Australia (BCA).
Following the 2009 bushfires in Victoria, the Regulations were amended with effect from 11 March 2009 and subsequent further amendments coming into affect from 9 March 2010. The Regulations as amended have the effect that a reference to a ‘designated bushfire prone area’ in AS 3959 – 2009 (the Standard) and Volumes One and Two of the BCA means the whole of Victoria.
As a result of the amendment all proposed Class 1, 2 or 3 buildings and associated Class 10a buildings throughout the state are subject to the site assessment provisions required by the Standard, though many sites will be assessed as BAL-LOW and will not be required to comply with additional construction requirements.
The Standard sets out construction requirements for a building determined according to the highest Bushfire Attack Level (BAL) of the site.
The BALs for which specific construction requirements
are set out in the Standard are:
There are no additional construction requirements for an assessment of BAL-LOW.
(3) DETERMINATION OF BAL
The applicant must arrange an assessment of the site and provide the Relevant Building Surveyor (RBS) with his or her analysis of the BAL. The BAL can be determined using either the simplified procedure set out in Clause 2.2 (Method 1) of the Standard, or the detailed procedure set out in Appendix B (Method 2).
Method 1 can be used for sites that have an effective ‘downslope’ under the classified vegetation between 0º and 20º.
Method 2 can be used for sites where the effective downslope under the classified vegetation is between 21º and 30º and the slope of the land between the site and the classified vegetation is no more than 20º regardless of slope type.
Method 2 should only be used to determine the BAL by a person with appropriate bushfire expertise, such as a fire safety engineer.
The Standard does not apply where the slope under the classified vegetation exceeds 30º downslope and where the slope of the land between the site and the classified vegetation is more than 20º regardless of slope type. In these instances the site assessment and design of the building’s construction requirements will need to be undertaken by a suitably qualified and experienced person such as a fire safety engineer. When a site is beyond the scope of the Standard, a site analysis will not result in a BAL being determined under the Standard.
(4) SITE ASSESSMENTS AND THE ROLE OF THE RBS
The role of the RBS is to independently determine compliance of a design with the Building Act 1993 (the Act) and the Regulations prior to issuing a building permit. As the site assessment is part of the design process, the RBS must not undertake the site assessment for the purposes of an application for the building permit. The RBS may carry out an on site checking process for the purpose of verifying the BAL and adequacy of design. The site assessment should include the appropriate information to enable the RBS to verify the assessment.
The application should include a site plan and other information that clearly identifies all the information regarding predominant vegetation and exclusions, slope location and direction, and relevant distances as set out in Clause 2.2.1 or Appendix B.
A pro-forma site assessment report for Method 1 is available on the Building Commission’s website. The pro-forma has been endorsed by the Australian Institute of Building Surveyors.
In some cases where the allotment is clearly in an area that can be easily designated as BAL-LOW, less detailed information may be acceptable to the RBS.
(5) SIMPLIFIED PROCEDURE (METHOD 1)
The Standard sets out a process using Method 1 in a sequential order for determining the BAL for sites where the effective slope under the classified vegetation does not exceed 20º downslope.
(5.1) Clause 2.2.1
Step 1 – Determine the relevant Fire Danger Index (FDI). In Victoria the FDI is 100 except for Alpine areas where it is FDI 50.
(5.2) Clause 2.2.3
Step 2 – Vegetation classification
The classification process is set out in Clause 2.2.3. The intention is to identify the predominant risk vegetation that may impact on the building in the event of a bushfire. In the majority of cases, the predominant risk vegetation will consist of naturally occurring formations of the groups of vegetation identified in figure 2.3 of the Standard (such as forests or woodlands). There will often be a definitive and identifiable ‘line’ of the edge of the vegetation.
Isolated trees that are forward of this line can be disregarded when measuring the distance from the building site to the line below the canopy of the predominant risk vegetation. Following classification of the vegetation, some vegetation groups may be excluded by being classified as BAL-LOW under Clause 126.96.36.199. Appendix 1 demonstrates the exclusions under Clause 188.8.131.52.
(5.3) Clause 184.108.40.206
Clause 220.127.116.11 requires vegetation to be classified by Reference to Table 2.3 and Figures 2.4(A) to 2.4(G). This requires assessment of all vegetation to at least within 100m of the buildings including garages and carports within 6m of the Class 1, 2, or 3 building.
Note: Where predominant risk vegetation extends beyond 100m of the building it should be taken into consideration along with vegetation within 100m of the site.
After the vegetation has been classified, low threat vegetation and non vegetated areas can be classified as BAL-LOW in accordance with Clause 18.104.22.168.
(5.4) Clause 22.214.171.124 – (see Appendix 1)
Exclusions – Low threat vegetation and non-vegetated areas
Clause 126.96.36.199 sets out vegetation that is regarded as low threat and non-vegetated areas that can be ‘excluded’ from the classification of the predominant risk vegetation.
This is achieved by classifying the types or groups of vegetation identified by the Clause as being BAL-LOW. Sub-clauses 188.8.131.52 (a) to (e) are self explanatory. Subclause (f) refers to ‘cultivated ornamental gardens’. This exclusion will apply to trees on private allotments where they are part of a garden, whether on a suburban, township or even lager rural allotment. The heat energy release of a bushfire is generated mostly by ground fuel and the understorey.
The canopy of a tree is regarded as low risk where there is not enough fuel in the understorey to promote ignition of the canopy. Generally, maintained gardens on private properties, where there is little or no understorey under trees to fuel a fire, are considered to be an exclusion under sub-clause (f).
(5.5) Clause 2.2.4
Step 3 – Distance of the site from classified vegetation
The distance is to be taken from the nearest part of the building, excluding the allowable encroachments listed in Note 1 of Figure 2.1, to a vertical line below the canopy of the classified (non-excluded) vegetation determined under step 2. For each vegetation type classified in Clause 2.2.3, determine the distance of the site (building) from the classified vegetation, measured in the horizontal plane. As stated in Note 2 of Figure 2.1, the area between the building(s) and the classified vegetation may contain vegetation that can be excluded in accordance with Clause 2.2.3.
(5.6) Clause 2.2.5
Step 4 – Effective slope of land under the classified vegetation
The ‘slope’ refers to the slope under the classified vegetation in relation to the building, e.g. a ‘downslope’ is sloping downwards as it runs away from the building. For each vegetation type classified in Clause 2.2.3, the effective slope (in degrees) of the land under the classified vegetation and whether it is an ‘upslope’ or ‘downslope’ in relation to the site must be noted.
(5.7) Clause 2.2.6
Step 5 – Determination of Bushfire Attack Level
Using the information obtained from steps 1 to 4, the BAL can now be determined for the site by selection from the relevant row and column from Table 2.4.2 for FDI 100 and Table 2.4.4 for FDI 50. This should be done for all classified vegetation from each part of the site, the highest BAL determining the design and construction requirements of the building.
(5.8) Clause 2.2.7
Step 6 – Determination of the appropriate construction requirements
Having determined the appropriate BAL, it is the responsibility of the designer to incorporate the appropriate construction requirements in the design from the relevant Clauses 3 and 5 to 9 of the Standard. These should be clearly indicated in plans and specifications provided to the RBS in the documents lodged for a building permit.
(6) CLASSIFICATION OF VEGETATION IN FIRE EFFECTED AREAS
Some concern has been raised about the assessment of areas that have been burnt during recent bushfires. The Standard requires vegetation to be classified into one of seven groups dependant on vegetation type, not on current fire load. Foliage cover is an element of the classification system but not the sole determinant of vegetation type.
For example, an area of more than 1ha of trees with a height greater than 30m should be classified as Group A Forest, even though the foliage cover may currently be less than 30 per cent. Having identified the height of trees and density of trunks and allotting the vegetation to a Group in accordance with Figure 2.3, the Standard assigns the appropriate fuel load to that Group when the BAL is determined under Table 2.4.2 or 2.4.4.
(7) ROLE OF THE BUILDING APPEALS BOARD
The Building Appeals Board (BAB) can deal with applications for modification or determination of compliance in the usual manner (refer to Practice Note 2006-39). An application could be made to the BAB to modify or vary certain requirements of the regulations, the BCA or the Standard, or for confirmation that a design complies with the BCA.
(7.1) Modification or variation of a building regulation
Section 160 of the Act provides that the BAB has the statutory jurisdiction to determine that a provision of the Regulations does not apply or applies with the modifications or variations specified in the application to a building or land specified in the application.
It is unlikely that the BAB would consider that all the provisions of AS 3959-2009 do not apply where the site is assessed as being in one of the five Bushfire Attack Levels that require a construction response.
However, there may be circumstances where an application for a modification or variation of the Regulations relating to the construction of buildings in bushfire areas is a valid alternative where it is considered that the building design or a component of the design need not fully comply with the relevant deemed-to-satisfy provision.
As is customary, the BAB will scrutinise applications for modifications or variations of a provision of the Regulations diligently in relation to the particular design and the circumstances applying to the site.
Any application to the BAB to modify the Regulations applying to construction requirements in bushfire prone areas should include a clear and well considered discussion as to the reason the particular regulation should be modified or varied.
The application should also include statistics, data, or other material that supports the discussion seeking the modification or variation and if applicable, it should clearly indicate any additional measure that is proposed that may substitute or mitigate the modified or varied regulation.
(7.2) determination in respect of building design
Section 160A of the Act provides that the BAB has the statutory jurisdiction to determine that a particular design of a building or an element of a building complies with the Act, the Regulations or any document applied, adopted or incorporated in the building regulations.
This provides an opportunity for an applicant to seek confirmation from the BAB that a design of a building or an element of the building that does not necessarily comply with the requirements of AS 3959-2009, still complies with the Regulations by meeting the relevant performance requirement/s of the BCA.
As with an application for a modification or variation of a Regulation, the application provided to the BAB to assess a determination under section 160A must clearly articulate a convincing case supported by statistics, data, or other material that will assist the BAB in making a determination that the design or element of design meets the relevant performance requirement.
(7.3) Alternatives to the deemed-to-Satisfy provisions – Alternative Solutions
There are a number of design solutions that may be used to achieve compliance with the Performance Requirements GP5.1 in BCA Volume One or P2.3.4 in BCA Volume Two as amended by the Regulations.
External Water Sprinkler/Drencher Systems
An Alternative Solution may include the installation of an external water sprinkler or drencher system. An EWSS should only be considered as one part of an entire property fire management plan. Other considerations include:
- Deciding to stay and defend the property, or evacuate early
- Building improvements, e.g. fire-retardant treatment
- Siting and access considerations
- Fuel management
- Water supplies
- Ongoing maintenance.
As there is no approved standard for such a system, it is recommended that verification of its suitability should be sought from the Building Appeals Board (BAB).
(8) WILDFIRE MANAGEMENT OVERLAYS
In some areas a Wildfire Management Overlay (WMO) may apply in a planning scheme. The WMO identifies areas where the intensity of wildfire is significant and likely to pose a threat to life and property.
The purpose of a WMO is to ensure that building development in areas subject to high fire risk includes appropriate fire protection measures.
These measures include:
- Adequate water supply
- Building siting design
- Fuel reduced areas around buildings.
A planning permit is required in an area covered by a WMO for buildings and works associated with specific land uses, including a new dwelling or a dwelling extension of more than 50 per cent of the existing floor area. An application for a planning permit must demonstrate how it will meet the fire protection measures.
(8.1) Interaction of Wildfire Management Overlays and bushfire building controls
The CFA document Building in a Wildfire
Management Overlay – Applicant’s Workbook 20101
provides a set of tools for the assessment of bushfire risk and management requirements, standard planning permit conditions that could be applied and guidance for Alternative Solutions if the standard conditions are not appropriate.
While managing for bushfire risk is complex, the workbook provides tailored solutions for less complex sites. In more complex sites applicants may need to seek professional assistance. The workbook will help you to identify if further professional assistance is necessary.
The workbook takes you through the necessary steps to apply for a planning permit in an area covered by a WMO, and provides instructions to help:
- Assess the bushfire risk
- Choose the most appropriate dwelling site, and
- Choose management actions to address bushfire risk by either:
» Selecting from a set of standard permit conditions which in less complex situations meet the requirements of the WMO, or
» Developing an Alternative Solution where the standard permit conditions cannot be implemented due to site constraints, or are not acceptable to the applicant or the council. The Alternative Solution will need to demonstrate that fire protection objectives will be met to the satisfaction of the CFA.
The workbook contains three options to obtain a planning permit in a WMO.
The appropriate option will depend on the features of the land, the risk of bushfire and other land management constraints that may apply. The CFA workbook prescribes minimum levels of construction (AS 3959-2009) of BAL 12.5 for Option One and BAL 29 for Option Two. Option Three requires an alternative means of addressing the requirements of the WMO.
The information required to assess a permit application is different for each. For further details refer to the CfA website.
Regulation 804 provides that where a planning permit is required for the construction of the building, and a site assessment for the purpose of determining the bushfire attack level for the site has been considered as part of the application for the planning permit, then the relevant building surveyor must accept that site assessment for the purpose of determining the construction requirements that are applicable to the building.
Appendix 2 provides an outline of the implementation process under planning and building controls.
If you have a technical enquiries please email email@example.com or phone 1300 815 127
Building Commission 733 BourKe Street Docklands VIC 3008
1 The CFA Applicants Workbook 2010 will be updated as recommendations of the Victorian Bushfires Royal Commission are implemented through the remainder of 2011. This Practice Note will be updated as these changes occur.
EXPLANTION AND EXAMPLE:
This diagram also demonstrates exclusions considered under clause 184.108.40.206 and the distances (where relevant) between the excluded vegetation and other excluded vegetation or classified vegetation, and the distances to the building.
Building site Road (see 220.127.116.11 (e) Less than 0.25 ha, less than 20m width, ≥20m from site
Vegetation more than 100m or other classified vegetation (see 18.104.22.168 (c) & (d))
from site (see 22.214.171.124 (a)
Less than 0.25 ha, ≥20m from site or other areas less than 0.25 ha (see 126.96.36.199 (c)) Allotment boundary
Implementation process for Bushfire Building and Planning Controls