Dual occupancy · Hornsby Shire Council
Duplexes in Hornsby
What a house block in Hornsby Shire Council's area needs before it can carry two homes: the LEP minimum (700 m²), whether the state 450 m² / 12 m Low and Mid-Rise rule reaches here, and how the two homes can be titled. Read from the LEP text; the address check applies it to your lot.
The minimums under the LEP
Attached dual occupancy 700 m² (detached 800 m²), 16 m frontage; 800 / 900 m² inside a heritage conservation area; since 31 October 2025.
Low and Mid-Rise
Inside the state Low and Mid-Rise area — within about an 800 m walk of a listed town centre or station — the Housing SEPP overrides the LEP: a dual occupancy on a lot of 450 m² with a 12 m frontage at the building line, FSR 0.65:1, 9.5 m high, in any R2 zone. Block Checker reads the centre layer on the Planning Portal and tells you which side of the line your lot is on. Bushfire-prone, flood-control and heritage land is carved out and the LEP figures come back.
Can I split it into two titles?
Inside the Low and Mid-Rise area (an 800 m walk of the listed centres), the state rule (Housing SEPP s 169) lets a duplex approved on or after 28 February 2025 be split onto two Torrens lots of at least 225 m² each, 6 m wide at the front building line — one home on each, both fronting the street, no battle-axe lots. So the 450 m² / 12 m minimum lot splits side by side into two 225 m² / 6 m lots. It does not cover strata subdivision.
Outside that area, or on bushfire-prone or heritage land, the council decides. The LEP's Lot Size Map sets the smallest lot a split can create, and strata title is the usual alternative. The address check tells you which applies to your block.
What the blocks here actually measure
We ran 25 real addresses in each of these Hornsby suburbs through the engine. Median lot and frontage, and how many of the blocks we checked could carry two homes today. A spread of the addresses the NSW geocoder returns, not a census of the suburb.
| Suburb | Median lot | Median frontage | Two homes | Granny flat |
|---|---|---|---|---|
| Pennant Hills | 889 m² | 19.6 m | 24 of 25 | 23 of 25 |
| Beecroft | 854 m² | 20.1 m | 22 of 25 | 24 of 25 |
| Cheltenham | 934 m² | 21.3 m | 22 of 25 | 22 of 25 |
| Mount Colah | 843 m² | 19.2 m | 18 of 25 | 22 of 25 |
| Berowra | 763 m² | 19.7 m | 17 of 25 | 24 of 25 |
| Berowra Heights | 783 m² | 18.0 m | 17 of 25 | 22 of 25 |
| Asquith | 760 m² | 16.8 m | 16 of 25 | 19 of 25 |
| Hornsby Heights | 923 m² | 18.1 m | 15 of 25 | 20 of 25 |
Getting it approved
A DA to Hornsby Shire Council is the universal route and the only one on heritage or constrained lots. A CDC from a private certifier under the Low Rise Housing Diversity Code fast-tracks a code-compliant pair (the greater of 400 m² and the council minimum, and 15 m at the building line — 12 m only where the parking comes off a lane or secondary road, no heritage, no bushfire). The Pattern Book pathway uses a pre-approved NSW design on a level lot that meets its tests — subject to survey (slope). Splitting the pair onto two titles is covered above.
What catches owners out here
- Frontage at the building line — the state rule measures width where the homes sit, not at the kerb; a splayed block can lose a metre.
- Just under — 449 m² is not 450 m². The area shown is the deposited-plan area; a registered survey settles it.
- Constraints — bushfire-prone, flood-control and heritage land takes the lot out of the state rules and the fast-track routes and back to the LEP figures and a DA.
- Easements and sewer — not on the public maps; order the section 10.7 certificate and the sewer diagram before you design.
Questions owners ask
What is the minimum lot size for a duplex in Hornsby?
700 m² under the LEP, with a 16 m frontage. Inside the state Low and Mid-Rise area, within about an 800 m walk of a listed centre or station, the test is 450 m² with a 12 m frontage at the building line instead.
Can I build a duplex on a 450 m² block in Hornsby?
Only inside the Low and Mid-Rise area, on R2 land that is not bushfire-prone, flood-controlled or heritage, and only with 12 m of frontage at the building line. Outside that area the council minimum applies.
Can I subdivide a duplex in Hornsby into two titles?
Inside the Low and Mid-Rise area, yes, for a pair approved on or after 28 February 2025: Torrens lots of at least 225 m² each with 6 m of frontage, no battle-axe. Outside it, the LEP and its Lot Size Map decide.
Do I need a DA for a duplex in Hornsby?
A DA to Hornsby Shire Council is the universal route. A code-compliant pair on a clear lot can go through a private certifier as a CDC under the Low Rise Housing Diversity Code, and a level lot that meets the tests can use a Pattern Book design, subject to survey.
More: the Hornsby Shire Council guide (granny flats, C4, links) · granny flats in Hornsby · duplex rules across NSW · the Low and Mid-Rise policy · the Pattern Book.
Enter the address — lot, frontage, zone, the Low and Mid-Rise line and the LEP minimum, in about ten seconds.