"Stay Safe"
If you are building or renovating in a bush fire prone area you will require a site assessment to determine the hazard level of your site. Harper Timber can advise you on the correct timber species to utilise if your site falls under any of the bush fire hazard levels.
Summary
In many parts of Australia, the construction of new buildings and additions to existing buildings will be assessed as being in a Bushfire-prone Area. The relevant Australian Standard - AS 3959 - provides six different Bushfire Attack Levels for proposed construction:
- BAL - LOW
- BAL - 12.5
- BAL - 19
- BAL - 29
- BAL - 40
- BAL - FZ (Flame Zone)
Each level is based on the assessed threat dependant on the relevant Fire Danger Index, the surrounding type of vegetation (e.g. forest, woodland, shrubland etc), the distance from the site to the vegetation and the 'effective slope' under the vegetation.
As the assessed threat increases, so do the restrictions on the building materials that may be used. Where there are restrictions on the building materials, timber is permitted in many applications as the tables on pages 3 through 6 'Simplified Bushfire Standard Complying Timber Construction in NSW' show.
Fire Retardent Timber Species
The type of timbers that are allowed are dependent on the Bushfire Attack Level of the site. These timber can be summarised as
- BAL12.5 and 19
- General Timber - Timber with density of 750 kg/m or greater, are timbers density at 12 percent moisture content. Suitable timbers are listed in AS 3959 Table E1.
- Joinery Timber (window and doors only) - Timber with density of 650 kg/m or greater, are timbers density at 12 percent moisture content. Suitable timbers are listed in AS 3959 Table E2.
- BAL29 - Bushfire resisting timber
- Can be timber with an inherent resistance to fire or fire retardant treated.
The following timber species have been tested and found to meet the required parameters without having to be subjected to fire retardant treatment:
| Image | Species | Durability Class (above ground) | Origin |
|---|---|---|---|
 |
Blackbutt | 1 | Australia |
 |
Ironbark Red / Grey | 1 | Australia |
 |
Spotted Gum | 1 | Australia |
 |
Merbau | 1 | Indonesia |
 |
River Red Gum | 1 | Australia |
 |
Turpentine | 1 | Australia |
 |
Silver Top Ash | 2 | Australia |
It should be noted that AS 3959 does not replace any other standards which might set out minimum requirements for construction in a particular area but rather AS 3959 sets out requirements which are dependent upon the degree of assessed threat posed by the Bushfire Attack Level (BAL) and which are additional to the requirements of those other standards.
Further Information
The external use of building materials in houses built in declared bushfire prone areas is controlled under the Building Code of Australia (BCA) Parts P2.3.4 and 3.7.4. Before the BCA requirements apply, the local authority must declare the area, in which a house is to be built, to be a bushfire-prone area.
Compliance with Australian Standard AS 3959 Construction of Buildings in Bushfire Prone Areas is 'deemed to satisfy' the BCA requirements for Class 1 Buildings along with the NSW Rural Fire Services - Planning for Bush Fire Protection 2006.
Simplified Bushfire Standard Complying Timber Construction in NSW
In NSW building regulations vary from the requirements in the Acceptable Construction Manual within the Building Code of Australia (BCA) which is AS 3959 Construction of Buildings in Bushfire-prone Areas standard. The table below incorporates the requirements of both AS 3959 Construction of Buildings in Bushfire-prone Areas 2009, as well as Planning for Bushfire Protection - Addendum: Appendix 3, NSW Rural Fire Service - Planning for Bush Fire Protection.
Although every effort was taken to reflect regulations of AS 3959 Construction of Buildings in Bushfire-prone Areas standard it is recommended this information sheet is used in conjunction with AS 3959, especially where in doubt.
Stairs Decks & Ramps
| Building Element | Subfloor Space | BAL - 12.5 and BAL - 19 | BAL - 29 | BAL - 40 | BAL - FZ |
|---|---|---|---|---|---|
|
Wall enclosing subfloor space |
Enclosed |
Less than 400mm from the ground or an external horizontal surface1 use timber framing providedthe framing is clad with non-combustible material such as fibre cement, bushfire-resisting timber2 or timber with density of 750 kg/m3 or greater. 400 mm or more above the ground there are no construction requirement any timber can be used4. |
Timber framingprovided the framing is clad with non-combustible material or bushfire-resisting timber2 |
Timber framingprovided the framing is clad with non-combustible clad, i.e. masonry or min 9 mm fibre cement |
NSW building regulations do not recognise deemed-to- satisfy construction solution within this BAL. Building designs will require an alternative solution |
|
Subfloor supports (posts, stumps, columns, stair stringers etc) |
Enclosed |
Any timber4 |
|||
|
Open |
Bushfire-resisting timber |
Metal |
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|
Deck/ramp bearers and joists |
Enclosed |
Any timber4 |
|||
|
Open |
Bushfire-resisting timber2 |
Metal, concrete or brick |
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|
Decking and stair treads |
Enclosed |
Bushfire-resisting timber2 |
Tiled or concrete decks |
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|
Open |
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|
Balustrades and Handrails |
Enclosed |
Less than 125 mm from any glazing or any combustible wall handrails and balustrades shall made from non combustible material or bushfire-resisting timber2 125 mm or more from the building handrails and balustrades have no requirement any timber can be used4 |
Less than 125 mm from any glazing or any combustible wall handrails and balustrades shall made from non-combustible material |
||
|
Open
|
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Elevated Floors & Subfloors
| Building Element | Subfloor Space | BAL - 12.5 and BAL - 19 | BAL - 29 | BAL - 40 | BAL - FZ |
|---|---|---|---|---|---|
|
Wall enclosing subfloor space |
Enclosed |
Less than 400mm from the ground or an external horizontal surface1 use timber framingprovided the framing is clad with non-combustible material such as fibre cement, bushfire-resisting timber2 or timber with density of 750 kg/m3 or greater. 400 mm or more above the ground there are no construction requirement any timber can be used4. |
Timber framingprovided the framing is clad with non-combustible material or bushfire-resisting timber2 |
Timber framing provided the framing is clad with non-combustible clad, i.e. masonry or min 9 mm fibre cement |
NSW building regulations do not recognise deemed-to- satisfy construction solution within this BAL. Building designs will require an alternative solution |
|
Subfloor supports (posts, stumps, columns etc) |
Enclosed |
Any timber4 |
|||
|
Open |
Bushfire-resisting timber |
Brick, steel or concrete stumps |
|||
|
Bearers and joists |
Enclosed |
Any timber4 |
|||
|
Open |
Less than 400 mm above the ground use Bushfire-resisting timbers2 or line the underside of the floor framing with fibre cement or sheet metal (roofing) 400 mm or more above the ground there are no construction requirement any timber can be used4 |
Any timber provided the underside of the lowest joist or bearer is protected with a non-combustible material such as a metal roof sheet or fibre-cement sheeting |
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|
Flooring |
Enclosed |
Any Timber4
|
|||
|
Open |
Less than 400 mm from the ground the underside is lined with sarking or mineral wool or Bushfire-resisting timbers2 400 mm or more above the ground there are no construction requirement any timber can be used4 |
Any timber provided the underside of the lowest joist or bearer is protected with a non-combustible material such as a metal roof sheet or fibre-cement sheeting |
|||
Walls
| Building Element | BAL - 12.5 and BAL - 19 | BAL - 29 | BAL - 40 | BAL - FZ |
|---|---|---|---|---|
|
External Wall Surface |
Less than 400mm above the ground or an external horizontal surface1 , the cladding is to be timber with density of 750 kg/m3 or greater3, bushfireresisting timbers2 or with noncombustible material 400 mm or more above the ground or an external horizontal surface1 there are no construction requirement: any timber can be used4 |
Bushfire-resisting timber and sarking required between cladding and framework. |
Non-combustible clad, i.e. masonry or min 9 mm fibre cement |
NSW building regulations do not recognise deemed-to- satisfy construction solution within this BAL. Building designs will require an alternative solution |
|
External Wall Framing |
Any timber4 |
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|
Internal Wall surface |
Any timber4 |
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|
Internal wall framing |
Any Timber4 |
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External Mouldings & Internal Timbers
| Building Element | BAL - 12.5 and BAL - 19 | BAL - 29 | BAL - 40 | BAL - FZ |
|---|---|---|---|---|
|
Internal wall framing |
Any timber4 |
NSW building regulations do not recognise deemed-to- satisfy construction solution within this BAL. Building designs will require an alternative solution |
||
|
Internal Timber (Doors, joinery, wall lining, ceiling linings, staircases, flooring over concrete slab etc) |
Any timber4
|
|||
Roof Framing
| Building Element | BAL - 12.5 and BAL - 19 | BAL - 29 | BAL - 40 | BAL - FZ |
|---|---|---|---|---|
|
Roof framing under compliant noncombustible roof covering5 |
Any timber4 |
NSW building regulations do not recognise deemed-to- satisfy construction solution within this BAL. Building designs will require an alternative solution |
||
Framing for Roofed Structures like Verandas, Garages, Carports
| Building Element | BAL - 12.5 and BAL - 19 | BAL - 29 | BAL - 40 | BAL - FZ |
|---|---|---|---|---|
|
Where attached structure separated from the building by a fire rated FRL 60/60/60 wall that extends to the underside of a noncombustible roof covering5 |
Any timber4 |
NSW building regulations do not recognise deemed-to- satisfy construction solution within this BAL. Building designs will require an alternative solution |
||
|
Where the roof of an attached structure is separated from the roof space of the main building by a masonry veneer wall, 90 mm thick |
Any timber4
|
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Notes
- An external horizontal surface or a ledge includes decks, carport roofs, awnings and similar elements or fittings having an angle less than 18 degrees to the horizontal and extending more than 110 mm in width from the wall or window or door.
- Bushfire-resisting timbers include Blackbutt, Merbau (Kwila) and Red Ironbark, River Red Gum, Spotted Gum, Silver top Ash and Turpentine.
- Timber with density of 750 kg/m3 or greater, are timbers density at 12 percent moisture content. Suitable timbers are listed in AS3959 Table E1.
- Consideration such durability, strength and appearance need to be considered in addition to bushfire requirements. These issues are not dealt in this guide.
- Complying roof systems include conventional non combustible roof and materials (tile, metal sheet) ensuring any gaps over 3mm are protected by ember guards. For further detail on sealants, skylights, etc refer to AS 3959.
- Wood Solutions Guide 04: Building with Timber in Bushfire-prone Areas is available for free at www.woodsolutions.com.au
Please also refer to the NSW Rural Fire Service for further details ››