Corner blocks in Australia: secondary street setbacks, truncations and driveways

A corner lot generally has one front setback, to the primary street, normally the street the lot is addressed to, plus a smaller secondary-street setback along the entire second street boundary. Under the NSW complying path, the secondary setback is 2 m for lots of 200–600 m², while the front setback on the same lot is 4.5 m¹.

What separates the secondary setback from a side setback is length. A side setback faces one neighbour; the secondary-street setback runs along the street-facing side of the lot. A 2 m rule along a 30 m boundary reserves 60 m² of ground.

Three corner-specific rules can apply to the same lot, the secondary street setback, the truncation which is the cut-off corner created at subdivision, and limits on where the driveway can meet the road.

A corner truncation is the cut-off corner created when a lot is subdivided, forming a triangular splay across the street corner that is shown on the plan of subdivision, the registered survey plan that creates the lot. The truncation helps maintain the width of the verge, the strip of public land between the kerb and the boundary, and preserves sight distance, the clear view a driver needs across the corner. Logan's planning scheme policy, one of the council documents reviewed here, states that truncations maintain the minimum verge width and minimum sight distance at an intersection⁵.

The size of the cut comes from the registered plan and relevant council standards. Peet's Village Green guidelines in Queensland refer corner lots to the stage's approved plan of development (POD) for truncations and setbacks⁶. Where the truncation forms part of the registered subdivision boundary, the lot boundary follows the cut and setbacks are measured from that boundary.

The Queensland code can also apply truncation rules where the plan created none. The QDC keeps fences, screens and retaining walls to no more than 1 m high within a truncation formed by three equal chords of a 6 m-radius curve at the corner of the two road frontages.² For shallow corner lots with an average depth of 24 m or less, reduced road setbacks apply only where nothing more than 2 m high stands within a 9 m by 9 m truncation at the corner. Estate guidelines can also apply their own dimensions: North Harbour's guidelines set corner truncation setbacks in their setback appendix and state that no separate truncation application is required where those dimensions are met⁴.

On the worked-example values used here, with a 4.5 m front and 2 m secondary setback, the splay itself removes little extra from the calculated buildable envelope. A splay of up to 4.5 m along each street sits wholly inside those two setback strips, based on the setback geometry used in the example. Its area is already outside the lot boundary where the truncation was created at subdivision, while driveway clearance rules can also be measured in relation to the same corner.

In a worked example using NSW complying-development setbacks for a 450 m² lot measuring 15 m by 30 m, the corner version has a calculated buildable envelope of 272.25 m², compared with 297 m² for the mid-block version. That is 24.75 m² less, or about 8% of the mid-block envelope¹. The whole difference comes from one substitution: a 2 m secondary-street setback where a 0.9 m side setback would otherwise apply.

The same substitution reduces the available buildable width. The mid-block 15 m lot offers 13.2 m between its side setbacks; the corner version offers 12.1 m, after allowing for one 0.9 m side setback and the 2 m secondary-street setback. A design 12.5 m wide would fit within the calculated mid-block envelope but not the corner-block envelope, before any truncation, driveway rule or easement is checked.

Builder-stated minimum block widths do not necessarily account for this difference. Among the 25 volume builders sampled, 1,027 of the 2,208 catalogue designs publishing a minimum width state 12.5 m or less, and on the worked-example values a design with a stated 12.5 m minimum fits the mid-block lot but not the corner version of the same lot¹⁰.