On today's small lots, your garage or house wall is often built on or close to the boundary. That wall has to be fire-rated, and if it's built wrong, it's a defect that's expensive to fix once the plasterboard is up and painted.

In Australia people call these walls firewalls, boundary walls, fire-rated walls or separating walls. Here's when you need one, how they're rated, and what to look for during your build.

When a house needs fire-rated construction

For houses (Class 1 buildings), the fire separation rules are in the NCC 2022 Housing Provisions, Part 9.2 for external walls and Part 9.3 for separating walls. The main situations are:

  • External walls close to a side boundary. An external wall within 900 mm of an allotment boundary, including a garage wall, needs fire-rated construction.
  • External walls close to another building. A wall within 1.8 m of another building on the same allotment (other than a small detached shed or garage) needs it too.
  • Walls between attached dwellings. Townhouses, duplexes and terraces need a fire-rated separating wall between each home.

Eaves, gutters and other parts of the roof close to the boundary also have rules, so ask your designer to show how the roof edge on the boundary side complies.

A common myth is that the NCC requires a fire-rated wall between a detached house and its own attached garage. It doesn't. The requirements come from how close the walls are to the boundary or to other buildings.

Queensland's boundary setback rules (in the Queensland Development Code and your local planning scheme) decide how close you're allowed to build. The NCC then decides how that wall must be built.

How fire-rated walls are rated

Walls are given a Fire Resistance Level (FRL), written as three numbers in minutes, such as 60/60/60:

  1. Structural adequacy: how long the wall keeps carrying its load.
  2. Integrity: how long it stops flames and hot gases getting through.
  3. Insulation: how long it stops the far side getting hot enough to ignite things.

60/60/60 is the common rating for houses and the walls between attached dwellings.

What fire-rated walls are made of

The most common systems in Queensland homes are:

  • Masonry, such as brick or block walls of the required thickness.
  • Lightweight framed systems using fire-rated plasterboard, often with mineral wool insulation, built exactly to the manufacturer's tested system.
  • Shaftliner or intertenancy systems between townhouses, where a fire-rated panel sits in a steel track between the two frames.

The key point is that a fire-rated wall is a system. The board type, number of layers, screw spacing, insulation, joint treatment and the way the wall meets the roof all have to match the tested design. Swapping one product for a cheaper one can void the rating.

timber framed construction with firewall shown
The dividing barrier between dwellings with mineral wool either side is the firewall/
Section through the head of a masonry fire wall below a concrete slab, with mineral wool in the deflection gap, fire-rated sealant both sides, steel angles fixed to the slab each side, and grouted reinforced cores.
Masonry construction is not immune to fire separation (mineral wool)

Penetrations are where it goes wrong

Every hole in a fire-rated wall is a weak point. Power points, pipes, cables, exhaust ducts and downlights all need fire-rated collars, sealants or covers that suit the wall system.

Renovations are the most common way these walls get compromised. Someone cuts in a downlight or runs a data cable through a boundary wall without sealing it, and the rating is gone. If you renovate later, tell your tradies which walls are fire-rated.

Can you design around it?

In rare cases a fire engineer can design a performance solution. Smoke alarms are required in every new home anyway, but they don't replace fire separation. For most new homes, the deemed-to-satisfy fire-rated wall is the simplest and cheapest path.

What to check during your build

  • At design: ask which walls are fire-rated, what FRL they need, and which system is specified. It should be on the drawings.
  • At frame stage: check the frame and any fire-rated elements match the system. My C7 Frame checklist covers this stage.
  • Before the walls are closed in: check the mineral wool, fire-rated board and penetration seals are in place, and that the wall continues right up to the roof sheeting or tiles as the system requires. The C11 Enclosed checklist helps here.
  • At handover: ask for the product details and any certificates for the fire-rated system, and keep them with your home's records.

Further reading

Timber vs Steel Framing: Choosing for Your HomeExplore the choice between timber and steel for lightweight framing in home construction. This guide compares their benefits, from environmental impact to cost and durability, helping you make an informed decision for your sustainable, efficient, and aesthetically pleasing home design.Framing Timbers: Choosing Between 90x35 MGP & LVL timberChoosing the right framing material is crucial in construction. This detailed guide compares the 90x35 MGP framing timber and the LVL laminated veneer lumber, to help you make an informed decision. We discuss the properties, advantages, and potential drawbacks of each option.Defining Plasterboard Finish Levels in ConstructionExploring the importance of specifying plasterboard finish levels for project builders to guarantee quality and client satisfaction.