Published · Clear Vision Glass & Glazing
A significant part of the Cardinia hills — Emerald, Cockatoo, Avonsleigh, Clematis, Gembrook, Beaconsfield Upper and Pakenham Upper among them — sits within designated bushfire-prone areas. If your property is in one, the glazing in your home is not simply a matter of preference. It is governed by AS 3959, and the requirements step up with your bushfire attack level.
This catches people out most often at exactly the wrong moment: a window breaks, they call for a replacement, and the answer is more complicated than matching what was there.
What BAL actually is
Bushfire Attack Level is an assessment of how much radiant heat and ember attack a building is likely to face, based on vegetation type, distance from that vegetation, and slope. It runs from BAL-LOW through BAL-12.5, 19, 29 and 40 up to BAL-FZ, the flame zone.
Windows matter disproportionately in a bushfire because glass fails from radiant heat well before a wall does, and once a window fails, embers get inside. Most homes lost in bushfires are lost to ember attack rather than to a wall of flame.
What it means for glazing
The requirements tighten progressively. At lower BAL ratings the emphasis is on screening and on protecting the lower portion of the glass. From BAL-29 upward, toughened glass becomes a requirement for the exposed portions of windows, and at BAL-40 and flame zone the specification extends to the framing, the seals and the screens as an integrated system.
Screens are part of the specification, not an accessory. Where screening is required it generally has to be a corrosion-resistant mesh with a specified aperture, fitted to the whole opening — an ordinary fibreglass flyscreen does not satisfy it.
Framing matters too. At higher ratings, unprotected timber framing is not compliant, and there are requirements around gaps and seals to prevent ember entry around the window rather than through it.
The practical situation when a pane breaks
If a window breaks in a bushfire-prone property, replacing like for like is not automatically the correct answer. Where the original glazing was installed to a BAL specification, the replacement needs to maintain it — putting ordinary annealed glass back into a window that was specified as toughened quietly removes protection the house was designed to have.
Where the home predates the current mapping, there is generally no obligation to retrospectively upgrade. But a broken pane is the cheapest opportunity you will ever get to improve it, because you are already paying for the labour.
What we do on a hills job is ask whether the property has a BAL assessment, look at what is actually in the window, and give you a straight answer about what the replacement should be. If you are unsure of your rating, your council or a bushfire assessor can confirm it — and if the property was built or extended in recent years, the rating will be in the building approval documents.
Worth doing at the same time
- Check the seals. Gaps around a window frame are an ember entry path, and perished seals are cheap to replace while the glass is out.
- Look at the screens. Corrosion-resistant mesh screening is a genuine ember defence and one of the more cost-effective improvements available.
- Consider toughened glass on the most exposed elevations even if your rating does not strictly require it. The cost difference on a pane you are already replacing is modest.
- Deal with what is stacked against the house. Firewood, mulch and outdoor furniture under a window increase the radiant load on that glass considerably.
Want this looked at?
We’re glaziers based in Pakenham servicing Cardinia Shire and the City of Casey. Free quotes, and for most jobs a photo is enough to get a price.
