New building standards for bushfire prone areas AS 3959 (Vic)

Following the recent bushfires the government has moved to introduce higher building standards in bushfire prone areas Victoria.

The Australian Building Codes Board (ABCB) endorsed the final draft version of the Australian Standards 3959 – Building in Bushfire Prone Areas, (AS 3959), which will be referenced by the Building Code of Australia (BCA) from May 2010. The ABCB has indicated it would assist any State that elected to adopt the new standard prior to 2010.

On the 6 March, the Victorian Government announced that it would adopt the new version of AS 3959, rather than an interim version that was initially considered. The new version of the Standard will apply in Victoria from 11 March 2009.

From that date, in Victoria, new building permit applications will be subject to the construction requirements under the new standard; the standard will apply to Class1 (houses) Class2 (apartments), Class 3 (residential buildings other than class 1 or 2) buildings and associated Class 10a buildings or carports, garages, sheds and the like.

Interim regulations have been introduced by the Victorian government to incorporate the new standard into Victoria’s legislation. The new regulations require that every new building permit in Victoria is subject to the new bushfire standard. This includes permits for new homes and renovations/additions.

The interim regulations can be accessed through:

http://www.dms.dpc.vic.gov.au 

The government has adopted a conservative approach and this may require a site assessment to be carried out subject to the discretion of the relevant building surveyor.

In most cases there should be no construction requirements for the majority of new designs as many areas in Victoria will have no or minimal risk of bushfire attack, the government estimate that around 80% of building permit applications will not be affected.

AS 3959 – 2009
The new standard is far superior to the existing 1999 version because it is easier to follow and is more realistic in approach.  Additionally, buildings at the lower levels of attack should be less costly to construct when compared to the existing standard, however buildings at the higher levels will be more costly.

The methodology for determining a given building’s construction requirements are:

1. Determine whether the building is in a designated bushfire prone area. (now all of Victoria)
2. Using the site classification procedure, determine the bushfire attack level (BAL)
3. Select the appropriate construction solutions for the BAL level

The ABCB Regulatory Impact Statement (RIS) on the standard to measure the cost versus the benefit offered three flame temperatures for consideration they were 960K, 1000K and 1090K.  The approved standard assumes a flame temperature of 1090K (approximately 816°C).

The site assessment procedure is based on scientific data and can be arrived at using either a simplified method within the body of the standard or fire engineering principles contained in Appendix B of the Standard.

The site classification process now includes a fire danger index (FDI) as well as factoring in more realistic slope aspects such as:

• the slope under the vegetation as well as the subject building;
• whether there is an upslope or downslope; and
• distance from the building to the vegetation.

There are now six levels of bushfire attack, compared to the existing three. The levels are based on heat flux exposure and range from Low to Flame zone:

• Low ＜12.5kW/m²
• 12.5 kW/m²
• 19 kW/m²
• 29 kW/m²
• 40 kW/m²
• Flame zone > 40 kW/m²

The standard goes onto to set out construction solutions for building within five of the six BAL levels from 12.5 kW/m² to Flame Zone. There are no construction requirements for the lowest level or BAL-LOW. These construction requirements increase in stringency as a direct relationship to the increase in BAL. 

AS 1530.8.2 Part 8.2 Tests on elements of construction for buildings exposed to simulated bushfire attack – Large flaming sources now provides methods for testing building materials, components and structures subject to bushfire attack. Many building components required in higher BALs are now required to be tested in accordance with this standard.

The new version of AS 3959 is available from the SAI Global bookstore – http://infostore.saiglobal.com/store/Details.aspx?ProductID=1101539.

Whilst HIA supports the introduction of the revised bushfire standard, HIA advocated the retention of a flame temperature of 1000K in preference to the 1090K option by the ABCB.  HIA also successfully argued for the retention of ‘deemed to satisfy’ building solutions for the more extreme bushfire classifications.

The new version of AS 3959 is not perfect; however it provides a significant improvement on the previous 1999 version. There are still some unresolved matters that the standards committee feel need to be included in the document.  These have been listed in the introduction to the standard and are expected to be resolved in due course.

Planning Permits

Currently there is what is referred to as Wildfire Management Overlays (WMO) in Victoria.

Generally when building in these areas a planning permit is required, this entails determining the BAL but also requires safety aspects such as provision of water and proper access for emergency vehicles.

The Victorian Government is streamlining the process for rebuilding homes destroyed by bushfire by removing the need for a planning permit where possible, where a house is being replaced on the same site.

Further interim bushfire regulations were introduced on 1 September 2009 to provide regulations around bushfire safety in relation to provision of water for fire suppression and access for emergency vehicles that would otherwise be covered under a WMO. It is now the responsibility of the relevant building surveyor to ensure that these measures are introduced in relation to bushfire safety matters.

The new further interim bushfire regulations can be accessed through: http://www.legislation.vic.gov.au/Domino/Web_Notes/

It is important to note that the exemption from planning only applies if rebuilding a home destroyed or damaged by the bushfires and does not exempt planning permits for other matters such as heritage, landslip or flooding overlays.

The government is unclear at this stage as to the actual siting of the home and if to avoid the need for a planning permit, if in a WMO; the house needs to be sited as before. The building surveyor would need to use his or her discretion in this.

Section 10 of the Building Act 1993

When applying for a building permit section 10(2) of the Building act 1993 will need to be considered. Section 10 allows that if substantial progress has been achieved on a particular design prior to the introduction of a new regulation and the building permit has not been issued then the relevant building surveyor can consider allowing the adoption of the previous regulations.

More details on Section 10(2) are set out in HIA's information sheet Transitional rules for new building regulations.

Finally it must be emphasised due to the nature of bushfires, construction in accordance with this standard will give no guarantee that the building will survive the fire.

For further information HIA members can contact HIA’s Building Services staff on 1300 650 620 or hia_technical@hia.com.au.   

If you would like to become a HIA member, contact 1300 650 620 or enquiry@hia.com.au

The above is intended to provide general information in summary form. The contents do not constitute specific advice and should not be relied upon as such. Formal specific advice should be sought by members with respect to particular matters before taking action. ABN 99 004 631 752