Can I build a duplex or granny flat in Allambie Heights?

The typical Allambie Heights block

The middle block of the 25 we checked is 697 m² with 18.3 m of street frontage. The smallest was 463 m² and the largest 1,011 m². Zones in the sample: R2 (24), RE1 (1).

What homes sell for in postcode 2100

Median sale prices for the whole of postcode 2100, January to March 2026. These cover every suburb sharing the postcode, not Allambie Heights alone, and they are not a value for any one block.

• Houses: $2.50m (37 sales)
• Units and apartments: $1.05m (11 to 30 sales, a small sample)

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

A granny flat

24 of the 25 blocks we checked could take one. Warringah LEP cl 5.4(9) — the greater of 60 m² or 11% 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 Allambie Heights

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

Under Warringah Local Environmental Plan 2011 a dual occupancy needs 800 m² — this LEP sets no frontage minimum, so Council's DCP governs width.

Of the 19 ordinary R2 blocks in our sample sitting outside the Low and Mid-Rise area, 6 had the 800 m². There is no LEP frontage test to pass here, but Council's DCP still judges width, setbacks and private open space, so clearing the area alone does not settle it.

Low and Mid-Rise

5 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

11 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 Allambie Heights 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 Allambie Heights. Your own block is the only one that answers for itself — that is what the box on the right is for.