Can I build a duplex or granny flat in Westleigh?

The typical Westleigh block

The middle block of the 25 we checked is 698 m² with 21.1 m of street frontage. The smallest was 391 m² and the largest 16,905 m². Zones in the sample: R2 (24), E1 (1).

What homes sell for in postcode 2120

Median sale prices for the whole of postcode 2120, January to March 2026. These cover every suburb sharing the postcode, not Westleigh alone, and they are not a value for any one block.

• Houses: $2.01m (42 sales)
• Units and apartments: $1.37m (49 sales)

Source: NSW Government Rent and Sales Report (Department of Communities and Justice), sales tables by postcode, NSW Government. Updated each quarter.

A granny flat

19 of the 25 blocks we checked could take one. Hornsby LEP cl 5.4(9) — the greater of 60 m² or 33% of the house’s total floor area, parking excluded. Separately, the state Housing SEPP allows a granny flat of up to 60 m² through the ten-day complying-development route on a lot of 450 m² or more with a 12 m frontage, where the land is not flood, bushfire or heritage constrained.

Dual occupancy (duplex) rules in Westleigh

8 of the 25 blocks we checked could carry two or more separate homes today.

Under Hornsby Local Environmental Plan 2013 a dual occupancy needs 700 m² and 16 m of frontage.

Of the 24 ordinary R2 blocks in our sample sitting outside the Low and Mid-Rise area — where that minimum is the only test that applies — 16 had the frontage and 11 had the land. 8 had both.

So in Westleigh it is the area that stops a second home more often than the frontage. A block short on land cannot be stretched, but two neighbouring blocks together clear it easily — which is why duplex sites here tend to be assembled in pairs rather than found.

Low and Mid-Rise

None of the 25 blocks we checked fell inside the state Low and Mid-Rise area, so in this part of Westleigh the LEP minimums are what count. The boundary is a walking distance from a listed centre, so it can cut through a suburb — the checker reads which side of it your own address sits on.

What else turned up

15 of 25 were on bushfire-prone land. Any of those takes a block out of the fast-track routes and into a full DA, so it changes the answer more than the lot size does.

How we got these numbers

We took 25 real Westleigh street addresses from the NSW geocoder and ran every one through the same engine this site runs for you, reading the planning controls live. Nothing here is modelled or estimated.

It is a sample, not a census. The addresses are a spread across what the geocoder returns, so treat these as "of the 25 blocks we checked" rather than a figure for every block in Westleigh. Your own block is the only one that answers for itself — that is what the box on the right is for.