The setback math. 4 numbers that decide what you can actually build.
Front, rear, side, and side again. Four setback numbers from the LEP determine the build envelope on your lot. Here is the worked example for a 600 square metre Brisbane corner lot.
The buildable area of a lot is not the same as the lot area. Council setback rules carve away a margin from every boundary, and what is left is the "build envelope" within which any new structure must sit.
Four setback numbers do the work. Front, rear, side (north or east), side (south or west). Get these four right and you know the maximum footprint your dwelling can occupy. Get them wrong and your architect bills you for the redesign.
This post explains where each number comes from, how to find it for your lot, and a worked example for a 600 square metre Brisbane lot.
The four numbers
Number 1: front setback
The minimum distance from the front lot boundary to the front face of the building. Typically 6 metres in most residential zones in Australia.
Variations:
- Some councils require an "averaged" front setback equal to the average of the two adjoining houses, to maintain streetscape character. Inner-Sydney heritage areas use this rule.
- Corner lots often have two front setbacks (one to each street frontage), with different rules for the "primary" and "secondary" frontage.
- Front setbacks may be reduced where the lot is shallow relative to depth. Some councils allow a 4.5-metre front setback if the lot is under 25m deep.
Number 2: rear setback
The minimum distance from the rear lot boundary to the rear face of the building. Typically 6 metres but with significant variation.
Variations:
- Some councils calculate rear setback as a percentage of the lot depth (e.g. 25% of depth, minimum 6m). On a 30-metre-deep lot this is 7.5m.
- Where the rear of the lot abuts public open space (a park, a reserve), the setback can be larger (often 9-12m) to provide a privacy buffer.
- Where the rear of the lot abuts a laneway, the setback can be smaller (3-4.5m) because the laneway already provides separation.
Number 3 and 4: side setbacks
The minimum distance from each side boundary to the side face of the building. Typically asymmetric: one side has a wider setback than the other.
Variations:
- The most common rule: 1.5m on one side, 1.0m on the other side, with the wider setback typically on the south or west to preserve solar access for the neighbour.
- For two-storey buildings, side setbacks increase: typically 1.5m at ground floor and 3m at first floor, or 1.0m at ground and 2.5m at first.
- For corner lots, the side that faces the secondary street is treated as a front setback (typically 3-4.5m), not a side setback.
Some councils use a "building envelope" calculation that prescribes an angled line from the boundary upward, which produces a different envelope than simple horizontal setbacks.
How to find the numbers
Three documents, in order of priority:
1. The zone provisions in the Local Environmental Plan (NSW) / Planning Scheme (QLD/VIC)
The LEP or scheme states the basic setback rules for each zone. For a "Low Density Residential" zone in NSW, the LEP refers to the DCP for setback specifics. For "Low-medium Density Residential" in Brisbane, the City Plan 2014 provides setbacks directly in the assessment criteria.
2. The Development Control Plan (DCP) for the zone
The DCP gives the specific numbers. Front setback, rear setback, side setbacks, and any conditions (corner lot, narrow lot, heritage character, etc.).
3. The lot's specific overlays
Some overlays modify the setbacks. Character areas may require a deeper front setback to match adjacent dwellings. Bushfire-prone areas may require additional rear setbacks for fire mitigation. Riparian overlays may require setbacks from waterways.
Worked example: 600 square metre Brisbane corner lot
A lot at the intersection of two streets, 20m wide on the primary street and 30m deep on the secondary street. Zone: Low-medium Density Residential. Lot area: 600 square metres.
Setbacks from Brisbane City Plan 2014:
- Front setback (primary street): 6m
- Front setback (secondary street): 3m (corner lot rule)
- Rear setback: 3m (because the secondary frontage substitutes for "rear")
- Side setback (remaining side): 1.5m at ground floor, 2.0m at first floor
Build envelope calculation:
- Lot is 20m wide, 30m deep.
- Subtract 6m primary front setback + 3m secondary frontage setback: 11m used
- Subtract 1.5m side setback: 1.5m used (the secondary frontage absorbs one "side")
- Subtract 3m rear setback: 3m used
Remaining width (east-west): 20m - 3m - 1.5m = 15.5m Remaining depth (north-south): 30m - 6m - 3m = 21m
Maximum single-storey footprint: 15.5m × 21m = 325 square metres Maximum FSR at 0.6:1 (typical for this zone): 360 square metres of total floor area
This is the buildable envelope. The actual dwelling will be smaller because internal walls, garages, and external features all sit within these limits.
The common mistakes
Three errors I see repeatedly:
Mistake 1: not checking corner lot rules
Many corner lots have an unexpected secondary-frontage setback. A buyer assuming a 1.5m side setback on the secondary frontage discovers, after architect engagement, that the actual setback is 3m and their planned garage no longer fits.
Mistake 2: ignoring averaged front setbacks
In streetscape-protected areas (heritage character, established suburbs), the averaged front setback rule can require a setback significantly more than the nominal 6m. If your two neighbours sit 9m and 11m back, your build must sit at the 10m average.
Mistake 3: treating two-storey setbacks as the same as ground-floor
The first-floor setback is typically 0.5-1.5m greater than the ground-floor setback. A buyer assuming "1.5m all the way up" loses 1m of buildable width on the upper floor and the architect has to redesign.
The two-minute check
Before you bid:
- Open the council DCP (or planning scheme equivalent).
- Look up the zone the lot is in.
- Read the four setback numbers (front, rear, side, side).
- Mentally subtract them from the lot dimensions.
The remaining rectangle is your build envelope. If it does not accommodate the size of dwelling you have in mind, the lot is wrong for your purpose.
The setback rules are public. Reading them takes minutes. The buyer who reads them buys a lot that fits the build they want. The buyer who does not reads them after exchange and pays the redesign cost.
