Bushfire Protection
Understanding Bushfire Protection Requirements
In bushfire-prone areas, protecting buildings from a fire is a critical part of modern building design. While gutters often attract significant attention, embers can also enter buildings through roof cavities, ventilation openings, gaps, weep holes and other vulnerable penetrations.
The Australian Standard for construction in bushfire-prone areas, AS 3959-2018, establishes specific requirements for building elements based on the assessed Bushfire Attack Level (BAL) of the site.
Karben Guard® provides a range of different mesh solutions designed to assist builders, roofers, installers and specifiers in addressing bushfire protection requirements across gutter guard and ember guard applications.
Gutter Guard vs Ember Guard: Understanding the Difference
By far, one of the most common misconceptions surrounding bushfire protection is that Gutter Guard products and Ember Guard products are subject to the same requirements. In reality, AS3959-2018 clearly distinguishes between gutter guards and ember guards and demands separate requirements for each of them.
Another mistaken belief, particularly with metal roofing applications, is that the gutter guard needs to also perform the role of ember guard. Most commonly the ember guard requirements associated with the underside of roof corrugations or at ridge lines, is dealt with via a combination of sarking or foil-backed insulation or other mineral wool products as referenced in the Standard.
Gutter Guard Requirements Under AS3959-2018
For gutter guard applications, AS3959-2018 places only one requirement on gutter and valley leaf guards across all Bushfire Attack Levels (BAL):
“If installed, gutter and valley leaf guards shall be non-combustible.”
5.6.7 Gutters and downpipes
This Standard does not provide material requirements for:
- gutters, with the exception of box gutters; and
- downpipes.
If installed, gutter and valley leaf guards shall be non-combustible.
Box gutters shall be non-combustible and flashed at the junction with the roof with non-combustible material.
6.6.7 Gutters and downpipes
This Standard does not provide material requirements for:
- gutters, with the exception of box gutters; and
- downpipes.
If installed, gutter and valley leaf guards shall be non-combustible.
Box gutters shall be non-combustible and flashed at the junction with the roof with non-combustible material.
7.6.7 Gutters and downpipes
This Standard does not provide requirements for downpipes.
If installed, gutter and valley leaf guards shall be non-combustible.
With the exception of box gutters, gutters shall be metal or uPVC.
Box gutters shall be non-combustible and flashed at the junction with the roof, with noncombustible materials.
8.6.7 Gutters and downpipes
This Standard does not provide requirements for downpipes.
If installed, gutter and valley leaf guards shall be non-combustible.
Gutters shall be non-combustible.
Box gutters shall be non-combustible and flashed at the junction with the roof with non-combustible materials.
9.6.7 Gutters and downpipes
This Standard does not provide requirements for downpipes.
If installed, gutter and valley leaf guards shall be non-combustible.
Gutters shall be non-combustible.
Box gutters shall be non-combustible and flashed at the junction with the roof with non-combustible materials.
Importantly, AS3959-2018 does not prescribe a maximum or minimum aperture size for gutter and valley leaf guards. The requirement relates solely to the combustibility of the product used.
Karben Guard® aluminium mesh products have been tested in accordance with AS/NZS 1530.3 and achieved a Spread of Flame Index of 0. As a coated metal product, this satisfies the relevant provisions of the National Construction Code and allows Karben Guard® aluminium mesh to be deemed non-combustible for use as a gutter and valley leaf guard at all BALs.
Ember Guard Requirements Under AS3959-2018
An ember guard serves a different purpose. AS3959-2018 defines an ember guard as a cover inserted in or over an opening or cavity to prevent the entry of burning embers. These applications may include ventilation openings, eaves, roof spaces, wall cavities, weep holes and other building penetrations.
AS3959-2018 references ember guards in Clause 3.6 and states:
“The maximum allowable aperture size of any mesh or perforated material used as a screen shall be 2 mm.”
For ember protection applications, in BAL-12.5, BAL-19 and BAL-29 the Standard requires:
“a mesh or perforated sheet that conforms with Clause 3.6 and is made of corrosion-resistant steel, bronze or aluminium”.
However, for ember protection applications in BAL-40 and BAL-FZ the Standard removes aluminium as an option.
5.6.3 Sheet roofs
Sheet roofs shall:
- be fully sarked in accordance with Clause 5.6.2, except that foil-backed insulation blankets may be installed over the battens; or
- have any gaps sealed at the fascia or wall line, hips and ridges by:
- a mesh or perforated sheet that conforms with Clause 3.6 and is made of corrosion-resistant steel, bronze or aluminium; or
- mineral wool; or
- a combination of any of Items (i), (ii) or (iii)
C5.6.3 Sarking is used as a secondary form of ember protection for the roof space to account for minor gaps that may develop in sheet roofing.
6.6.3 Sheet roofs
Sheet roofs shall:
- be fully sarked in accordance with Clause 5.6.2, except that foil-backed insulation blankets may be installed over the battens; or
- have any gaps sealed at the fascia or wall line, hips and ridges by:
- a mesh or perforated sheet that conforms with Clause 3.6 and is made of corrosion-resistant steel, bronze or aluminium; or
- mineral wool; or
- a combination of any of Items (i), (ii) or (iii)
C6.6.3 Sarking is used as a secondary form of ember protection for the roof space to account for minor gaps that may develop in sheet roofing.
7.6.3 Sheet roofs
Sheet roofs shall:
- be fully sarked in accordance with Clause 5.6.2, except that foil-backed insulation blankets may be installed over the battens; or
- have any gaps sealed at the fascia or wall line, hips and ridges by:
- a mesh or perforated sheet that conforms with Clause 3.6 and is made of corrosion-resistant steel, bronze or aluminium; or
- mineral wool; or
- a combination of any of Items (i), (ii) or (iii)
C7.6.3 Sarking is used as a secondary form of ember protection for the roof space to account for minor gaps that may develop in sheet roofing.
8.6.3 Sheet roofs
Sheet roofs shall:
- be fully sarked in accordance with Clause 5.6.2, except that foil-backed insulation blankets may be installed over the battens; or
- have any gaps sealed at the fascia or wall line, hips and ridges by:
- a mesh or perforated sheet that conforms with Clause 3.6 and is made of corrosion-resistant steel, bronze; or
- mineral wool; or
- a combination of any of Items (i), (ii) or (iii)
C8.6.3 Sarking is used as a secondary form of ember protection for the roof space to account for minor gaps that may develop in sheet roofing.
9.6.3 Sheet roofs
Sheet roofs shall conform with:
- Appendix H; or
- a system tested to AS1530.8.2
While Karben Guard® 1.9mm Aluminium Mesh is suitable for use as gutter guard across all Bushfire Attack Levels, its use as an ember guard is limited to applications within BAL-12.5, BAL-19 and BAL-29.
Karben Guard® 1.9mm Stainless Steel Ember Guard Mesh
Manufactured from corrosion-resistant stainless steel with a durable powder-coated finish, Karben Guard® 1.9mm Stainless Steel Ember Guard Mesh has been developed specifically for ember protection applications requiring corrosion-resistant steel screening materials.
The product is suitable for ember guard applications within BAL-12.5, BAL-19, BAL-29, BAL-40 and BAL-FZ construction requirements where a corrosion-resistant steel mesh with a maximum aperture not exceeding 2mm is required under AS3959-2018.
While stainless steel mesh can provide a solution for the highest Bushfire Attack Levels, it is important to understand the implications of using stainless steel in contact with other building materials. BlueScope’s technical guidance on dissimilar metals identifies stainless steel and zinc/aluminium coated steel products as generally incompatible in direct contact due to the potential for galvanic corrosion of the less noble metal.
See extract from BlueScope Dissimilar Metals Technical Bulletin (CTB-12)
For this reason, Karben Guard® Stainless Steel Ember Guard Mesh is primarily intended for specialised ember protection applications where they are not in direct contact with other metals. Designers, builders and installers should carefully consider material compatibility and refer to the relevant manufacturer recommendations before specifying stainless steel mesh in conjunction with roofing and guttering products manufactured from galvanised steel, Zincalume® steel or similar coated steel substrates. The durable powder coating potentially offers some level of separation between dissimilar metals but Karben Industries does not in any way claim that this coating alone can provide the level of separation needed to ensure there is no reaction between dissimilar metals and does not recommend the use of this product in contact with any other metal materials.
