Bushfire construction requirements

Homeowners with builder in home being built.jpg

This is general advice and may not apply specifically to your property. For more detailed information on your personal circumstances please contact the Rebuilding Planning Team on 9294 6594.

AS 3959 is the Australian Standard that applies to bushfire requirements when building properties in Victorian. 

As BAL ratings increase, the use of non-flammable materials and methods of construction becomes more important.

Ember risk

Embers can enter through gaps as small as two millimetres. It’s important that the products and materials used are high quality so there are no gaps or holes left through which embers can enter the roof space, walls or underfloor. At higher BAL ratings, both the underside of the roof as well as above the ceiling should be covered and sealed with non-flammable insulating blankets to minimise ember entry.

Glass and windows

Glass and windows become more expensive at higher BAL ratings (e.g. BAL 40 & BAL FZ), so think carefully during the design phase about where glass is going and whether you will use window fire shutters.

Materials

Manufacturers have developed a wide variety of building materials, products and systems of construction that are suited to building in bushfire prone areas. Your designer or builder can recommend products that best suit your needs.

Some common materials used for external cladding or primary construction include corrugated and other steel profiles, fibre cement sheet or moulded panels of the correct thickness, brick, cement, rammed earth, and some timbers in lower BAL categories. Fire resistant sarking, roof and wall insulation products and sealants are also available.

Piping

Plastic pipe may be exposed to heat and melt creating an entry point for embers. The construction standards regulate these materials at higher BAL levels.

Sprinklers

Fire sprinkler systems can be considered, but they do not replace the need for the basic construction to be suited to the level of bushfire risk. This is particularly the case for a new build where eliminating combustible materials from the exterior of the building will generally be more effective and cheaper than a sprinkler system.

There are a range of bushfire sprinkler systems that can be designed into the roof construction or retrofitted to an existing structure. Avoid any designs that can trap embers and other materials on the roof.

Shelters

Victorian planning and building requirements also allow landowners to construct a private bushfire shelter or bunker. The installation of a private bushfire shelter does not remove the need for the house to comply with all the other planning and building requirements.

Costs

At lower BAL ratings, there are no fundamental changes for materials and construction methods that go over and above a typical building project.

At higher BAL ratings (40 and FZ), glazing costs increase, as do costs if shutters or other methods are implemented. Siting your structure to achieve a lower BAL exposure can have a big impact on costs for windows and glazing.

The table below lists what construction requirements there are for subfloor, floor, external walls and external walls and external windows. BAL - LOW has no special construction requirements and is therefore not included in this table:

BAL - 12.5
BAL - 19
BAL - 29 BAL - 40
BAL - FZ
Subfloor supports No special
construction
requirements
No special
construction requirements
Enclosure by external wall or by steel, bronze or aluminium mesh, non-combustible supports where the subfloor is unenclosed, naturally fire resistant timber stumps or posts on 75mm metal stirrups If enclosed by external wall refer below ‘External Walls’ section in table or non- combustible subfloor supports or tested for bushfire resistance to AS1530.8.1 Subfloor supports – enclosure by external wall or non-combustible with an FRL of 30/-/- or be tested for bushfire resistance to AS1530.8.2
Floors No special
construction
requirements
No special
construction
requirements
Concrete slab on ground, enclosure by
external wall, metal mesh as above or
flooring less than 400mm above ground
level to be non-combustible, naturally fire resistant timber or protected on the underside with sarking or mineral wool insulation
Concrete slab on ground, enclosed by external wall or protection of underside with non-combustible material such as fibre cement sheet or be non-combustible or be tested for bushfire resistance to AS1530.8.1

 

Concrete slab on ground or enclosure by external wall or an FRL of 30/30/30 or protection of underside with 30 minute incipient spread of fire system or to be tested for bushfire resistance to AS1530.8.2

 

External walls As for BAL - 19 External walls - Parts less than 400mm above ground or decks etc to be of non-combustible material 6mm fibre cement clad or bushfire resistant/ naturally fire resistant
timber
Non-combustible material (masonry, brick veneer, mud brick, aerated concrete, concrete), timber framed, steel framed walls sarked on the outside and clad with 6mm fibre content sheeting or steel sheeting or bushfire resisting timber

 

Non-combustible material (masonry, brick veneer, mud brick, aerated concrete, concrete), timber framed, steel framed walls sarked on the outside and clad with 9mm fibre content sheeting or steel sheeting or be tested for bushfire resistance to AS1530.8.1 Non-combustible material (masonry, brick veneer, mud brick, aerated concrete, concrete) with minimum thickness of 90mm or an FRL of -/30/30 when tested from outside or be tested for bushfire resistance to AS1530.8.2
External windows As for BAL-19 except that 4mm Grade A safety glass can be used in place of 5 mm toughened glass

 

Protected by bushfire shutter, completely screened with steel, bronze or aluminium mesh or 5mm toughened glass or glass blocks within 400mm of ground, deck etc. Openable portion metal screened with frame of metal or metal reinforced PVC-U or bushfire resisting timber Protected by bushfire shutter, completely screened with steel, bronze or aluminium mesh or 5mm toughened glass or glass with openable portion metal screened and frame of metal or metal reinforced PVC-U or bushfire resisting timber and portion within 400mm of ground level screened Protected by bushfire shutter or 5mm toughened glass. Openable portion screened with steel or bronze mesh

 

Protected by bushfire shutter or FRL of -/30/- and openable portion screened with steel or bronze mesh or be tested for bushfire resistance to AS1530.8.2