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Enclosing an alfresco in a bushfire-prone area: BAL ratings explained

What a BAL rating means for the glass and frames when you enclose an alfresco in a Victorian Bushfire Prone Area, and what to check before you order.

By Glassy Slide teamPublished 3 min read

A rendered alfresco on a timber deck enclosed with frameless glass, with trees beyond the back fence

Parts of Melbourne's outer north-east and east sit close to bushland. If your home is in a mapped Bushfire Prone Area, enclosing an alfresco comes with one extra step before the glass is ordered: a Bushfire Attack Level, or BAL, assessment.

What a BAL rating is

The BAL measures how much ember attack, radiant heat and flame a building could face in a bushfire. It is set from the vegetation near your home, its distance from the house and the slope of the land. The levels run from BAL-LOW, through BAL-12.5, BAL-19, BAL-29 and BAL-40, to BAL-FZ (flame zone).

The higher the level, the stricter the construction requirements in the Australian Standard AS 3959, which covers frames, glass, seals and screens for windows and doors.

When it applies to an alfresco enclosure

In a Bushfire Prone Area, building work that needs a building permit, including many extensions and patios, has to meet the bushfire construction rules, and the building surveyor works out the BAL for your site. Enclosing an alfresco is building work that needs a building permit (see do you need a permit to enclose an alfresco?), so the BAL is part of that process. The surveyor may look at the existing roof, posts and floor of the alfresco as well as the new glass and doors. Bushfire prone areas themselves are mapped by the state, not by your council.

In some areas a Bushfire Management Overlay also applies. It is a planning control that can bring a planning permit and a bushfire assessment on top of the building permit. Small alterations to an existing home can be exempt, but whether yours is depends on the work, including how much floor area it adds, so ask your council. VicPlan shows whether your address has an overlay. If a planning permit has already set a BAL for your site, the building surveyor works from that BAL.

Step 1: check your address

Bushfire Prone Areas are mapped property by property. Look up your exact address on VicPlan, or ask your council. Don't assume from the suburb: two streets apart can differ.

Step 2: get the BAL assessed

If you're in a mapped area, a building surveyor, or a bushfire consultant, assesses the site and gives you a BAL. For a building permit the building surveyor sets the BAL; a consultant's report is usually needed when a planning permit is involved. Do this before your glazier finalises the quote, because the BAL decides what the glass and frames must meet.

Step 3: specify the glass and frames to suit

At the lower levels the requirements are less demanding; at the higher levels, glass type and thickness, frame materials, seals and ember screens all become specific. The details sit in AS 3959 and are confirmed by your building surveyor. A quote for an enclosure in a bushfire area should say which BAL it's built to.

A rendered alfresco on a timber deck enclosed with frameless glass, an outdoor kitchen and barbecue visible inside
A real Glassy Slide job: a glass-enclosed alfresco. In a Bushfire Prone Area, the glass and frames are specified to the site's BAL.

Materials to think twice about

  • Polycarbonate roofing and panels can melt and drip in a fire, and many products don't meet the requirements at the higher levels. Near bushland, glass or metal is usually the better choice.
  • Timber decking and posts under or around the enclosure have their own AS 3959 requirements.
  • Gaps and seals. Embers get in through gaps. Well-sealed frames matter more here than anywhere.

Keep the rest of the plan the same

A BAL rating doesn't stop you enclosing an alfresco. It shapes the specification and can add to the cost of glass and frames at higher levels. For typical prices, see our alfresco enclosure cost guide.

We measure on site and quote in writing, with the glass and frames listed for each side. If your home is in a Bushfire Prone Area, tell us the BAL when you ask for a quote, and we'll tell you plainly whether we can build to it. See our alfresco enclosures or ask for a quote.

This guide explains the general rules. Your BAL assessment, building surveyor and council make the decisions for your property.

Questions

Is my suburb bushfire-prone?

Check your exact address on VicPlan. Bushfire Prone Areas are mapped property by property, so two streets in the same suburb can differ. Councils near bushland, including parts of Melbourne's outer north-east and east, have mapped areas.

Who does a BAL assessment?

For a building permit, the building surveyor sets the site's Bushfire Attack Level, based on the vegetation, its distance from the house and the slope of the land. A bushfire consultant usually prepares the assessment when a planning permit is involved.

What glass is needed at BAL-19 or BAL-29?

The Australian Standard AS 3959 sets the requirements for frames, glass, seals and screens at each level. They get stricter as the level rises. Your BAL assessment and building surveyor confirm what applies, and the glazing is specified to suit.

Is polycarbonate allowed?

It depends on the BAL and where it's used. Polycarbonate can melt and drip in a fire, and many products don't meet the higher levels, so it is often not a good choice near bushland. Ask your building surveyor.

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#alfresco enclosure#bushfire#bal rating#safety glass

Glassy Slide team

We supply and install double-glazed aluminium windows and doors, alfresco enclosures and glass partitions, and repair timber windows across Melbourne from our base in Bundoora. 5.0 ★ on Google.

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