Suburb guide · 2092
Can I build a duplex or granny flat in Seaforth?
Seaforth sits in Northern Beaches Council's area under Manly Local Environmental Plan 2013. We ran 25 real Seaforth addresses through the checker: the typical block is 692 m² with 14.9 m of frontage, 19 of the 25 could add a granny flat, and 22 could carry two separate homes today.
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The typical Seaforth block
The middle block of the 25 we checked is 692 m² with 14.9 m of street frontage. The smallest was 416 m² and the largest 1,378 m². Zones in the sample: R2 (21), C3 (2), SP2 (1), R1 (1).
The 25 blocks we checked, by land size.
What homes sell for in postcode 2092
Median sale prices for the whole of postcode 2092, January to March 2026. These cover every suburb sharing the postcode, not Seaforth alone, and they are not a value for any one block.
- Houses: $3.93m (11 to 30 sales, a small sample)
- Units and apartments: not published (10 or fewer sales this quarter)
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. Manly LEP cl 5.4(9) sets the size as the greater of 60 m² or 30% of the house’s floor area — not the 60 m² flat cap; cl 6.22 allows up to 75 m² where the flat sits entirely inside the existing house. 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 Seaforth
22 of the 25 blocks we checked could carry two or more separate homes today.
Manly LEP sets no minimum lot size or frontage for a dual occupancy — permitted with consent in R2, judged on Council's DCP controls (site coverage, setbacks, open space, parking)
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 Seaforth 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
6 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. Northern Beaches has no flood layer on the Planning Portal, so flood is checked against Council’s own study by hand.
How we got these numbers
We took 25 real Seaforth 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 Seaforth. 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.