Suburb guide · 2084
Can I build a duplex or granny flat in Duffys Forest?
Most of Duffys Forest is land this tool does not answer for. 25 of the 25 blocks we checked sit in rural, conservation, industrial or special-purpose zones rather than a residential one, and Block Checker covers residential zones only. The counts below are what it could assess — they are not a finding that nothing can be built. For land like this, a planner reads the LEP for the zone directly.
Duffys Forest sits in Northern Beaches Council's area under Warringah Local Environmental Plan 2011. We ran 25 real Duffys Forest addresses through the checker: the typical block is 20,199 m² with 110.2 m of frontage. Most of them are not residential land, so see the note below before reading the counts.
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The typical Duffys Forest block
The middle block of the 25 we checked is 20,199 m² with 110.2 m of street frontage. The smallest was 2,096 m² and the largest 125,253 m². Zones in the sample: RU4 (25).
The 25 blocks we checked, by land size.
A granny flat
0 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 Duffys Forest
0 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.
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 Duffys Forest 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
19 of 25 were on bushfire-prone land; 1 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. 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 Duffys Forest 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 Duffys Forest. 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.