Roofing
Ember Guard Mesh Calculator
Calculates ember guard mesh area for vents and openings to AS 3959
Updated 26 June 2026 · Live
What this tool does
Calculates the ember guard mesh area required to screen vents, weepholes and openings in a bushfire-prone area, from opening sizes and count.
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How the ember guard mesh calculator works
This calculator multiplies each opening’s width by its height to get the net area in square metres, multiplies by the number of openings, and adds 10% for cutting and overlaps. It covers the screening of vents, weepholes, evaporative-cooler openings and subfloor vents required in bushfire-prone areas.
AS 3959 and BAL ratings
AS 3959 requires openings in the building envelope to be screened with corrosion-resistant mesh of aperture no greater than 2 mm — typically aluminium, steel or bronze depending on the Bushfire Attack Level (BAL). The higher the BAL, the more elements must be screened. This tool estimates the mesh area; it does not assign your BAL, which must come from a bushfire assessment.
Where ember mesh goes
Common locations are roof and eave vents, weepholes in brickwork, subfloor and underfloor vents, and gaps around evaporative coolers. Measure each opening and group similar sizes to total the area.
What this tool does not do
It estimates mesh area only. It does not determine your BAL, specify the mesh alloy, or certify compliance. Confirm requirements with your bushfire consultant or building surveyor.
Adjusting the defaults
Every input is editable. Enter your own opening sizes and count and the mesh area recalculates instantly. Run it once per size group and sum the results for a mixed set of openings.
On-site considerations
Ember guard mesh must be fixed so embers cannot bypass it — continuous behind vents and tight to weepholes, with corrosion-resistant fixings that suit the mesh alloy. Aluminium mesh is easy to work but lower-rated than steel or bronze; match the alloy to your BAL. Allow extra at junctions where the mesh wraps a corner or steps over a flashing.
Using this alongside other BuildMetricLab tools
Pair this with the bushfire static water and roof ventilation calculators when preparing a bushfire-compliant build, and with the material cost calculator to price the mesh and fixings. Every BuildMetricLab tool runs entirely in your browser — no sign-up, no data sent anywhere, and every formula is shown on-page so you can audit the maths.
Sources & methodology
Calculates ember guard mesh area as opening width × height (converted from millimetres to square metres), multiplied by the number of openings, with a 10% allowance for cutting and overlaps. Every result is calculated from the values you enter, and all inputs are editable.
Frequently asked questions
Are ember guard mesh calculator results accurate enough to order mesh?
Use them as a starting estimate only. Verifying the final quantity with your supplier or contractor before ordering is good practice — site conditions, wastage and cut-offs all affect the true figure.
What wastage percentage should I use?
The calculator defaults to the typical Australian trade allowance for windows & doors. Increase it for complex cuts, awkward shapes, or first-time DIY. The default wastage allowance reflects common trade practice; values lower than the default may underestimate offcuts.
Does this replace professional advice?
No. This tool is a planning estimator. For works that affect structure, the National Construction Code (NCC), boundary or dividing-fence, gas, electrics, drainage to a sewer, or similar, consult a suitably qualified professional.
Can I change the unit prices?
Yes — every price field is editable. Plug in your supplier's quote to get a total that matches your project.
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