Eaves height (AS 4055)
AS 4055 applies to housing with eaves height up to 6.0 m above averaged ground level. Above that, design drops out of AS 4055 and into AS/NZS 1170.2.
Ask Chalkline about this →Eaves height is the vertical distance from averaged ground level to the underside of the eaves (the lowest point of the roof overhang at the wall line). The term is defined in AS 4055:2021, Wind loads for housing, and it sets one of the scope-limit gates for the Standard.
The 6.0 m eaves height limit.
AS 4055 only applies to housing where eaves height is ≤ 6.0 m above averaged ground level. Above 6.0 m, the build drops out of AS 4055 and the engineer must use AS/NZS 1170.2:2021 for wind design instead. Other AS 4055 scope gates that work alongside the eaves height rule:
| Scope gate | AS 4055:2021 limit |
|---|---|
| Eaves height | ≤ 6.0 m above averaged ground level |
| Roof apex height | ≤ 8.5 m above averaged ground level |
| Roof pitch | 1° to 35° (gable, hip, monopitch) |
| Floor area (each floor) | ≤ 300 m² |
| Plan length-to-width ratio | ≤ 5:1 |
| Site terrain | Categories TC1 through TC4 |
When ANY of these gates fails, the design must go to AS/NZS 1170.2.
Why builders need to know:
- Two-storey + raised slab on a sloping block: a 2,400 mm slab edge + two-storey wall plate + soffit drop can easily push eaves height over 6.0 m on the downhill side.
- Attic conversion: lifting the roof for an attic dormer can push the eaves of the dormer over 6.0 m.
- Highset Queenslander: a traditional highset on stumps with a raised floor and gable roof can be on the line.
- Skillion roof with high low-end: the eaves on the high side count, not the low side. A 1.5 m skillion drop adds 1.5 m to one eaves vs the other.
How to measure:
- Survey averaged ground level (the average of the natural ground level at the four building corners after any cut-and-fill works are completed).
- Measure from that datum to the bottom of the eaves at each corner.
- The highest eaves height is the controlling value.
On a sloping block, the downhill eaves is typically the controlling value because averaged ground level sits below the downhill natural ground level.
Consequences of crossing the 6.0 m line:
- AS 4055 wind classification (N1, N2, N3, etc.) no longer applies. The engineer issues a site-specific wind design under AS/NZS 1170.2.
- Bracing schedules in AS 1684 are written around AS 4055 wind classifications. A 1170.2 site needs custom bracing design.
- Truss design charts in manufacturer catalogues are typically AS 4055 zones; custom design needed above 6.0 m.
- Cost impact: site-specific engineering typically adds $1,500 to $4,000 to a residential job.
For builders:
- Measure eaves height at concept stage before lock-in. Discovering at the structural certificate stage that the build is 200 mm over the limit forces a redesign.
- On sloping blocks, ask the engineer early whether the eaves height is comfortably within scope, marginal, or out of scope. Marginal builds are at risk of crossing the line with normal construction tolerance.
- Don’t confuse with overall building height: planning rules typically cap overall height at 8.5 m (Housing Code NSW, similar elsewhere). AS 4055’s 6.0 m eaves height is a structural-engineering scope gate, not a planning-height gate. Different rules.
Also known as: roof eaves height, wall plate height.
Category: Structural / wind design / AS 4055.
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Last updated: 2026-05-15. Verified: 2026-05-15.