Suburb guide · 2088
Can I build a duplex or granny flat in Mosman?
Mosman sits in Mosman Council's area under Mosman Local Environmental Plan 2012. We ran 25 real Mosman addresses through the checker: the typical block is 574 m² with 12.4 m of frontage, 21 of the 25 could add a granny flat, and 8 could carry two separate homes today.
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The typical Mosman block
The middle block of the 25 we checked is 574 m² with 12.4 m of street frontage. The smallest was 225 m² and the largest 1,182 m². Zones in the sample: R2 (10), C4 (10), R3 (5).
The 25 blocks we checked, by land size.
What homes sell for in postcode 2088
Median sale prices for the whole of postcode 2088, January to March 2026. These cover every suburb sharing the postcode, not Mosman alone, and they are not a value for any one block.
- Houses: $5.73m (36 sales)
- Units and apartments: $1.25m (94 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
21 of the 25 blocks we checked could take one. Mosman LEP cl 5.4(9) — the greater of 60 m² or 43% 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 Mosman
8 of the 25 blocks we checked could carry two or more separate homes today.
cl 4.1B — a lot at least the Lot Size Map minimum for your land; no LEP frontage minimum (Council's DCP applies)
Low and Mid-Rise
7 of the 25 blocks sat inside the state Low and Mid-Rise area — within about an 800 m walk of a listed centre or station. Inside it the Housing SEPP overrides the LEP minimums: a dual occupancy on 450 m² with a 12 m frontage, terraces on 500 m² / 18 m, townhouses on 600 m² / 12 m and a manor house on 500 m² / 12 m, up to 9.5 m. That is what lifts the two-homes figure above; a block one street outside the line gets the LEP figure instead.
What else turned up
5 of 25 were on bushfire-prone land; 3 of 25 carried a heritage listing or conservation area. 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 Mosman 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 Mosman. Your own block is the only one that answers for itself — that is what the box on the right is for.
Enter the address — lot, frontage, zone, constraints and what it can carry.