Secondary dwelling · Blue Mountains City Council
Granny flats in Blue Mountains
How big a granny flat can be on a house block in Blue Mountains City Council's area — the LEP's cl 5.4(9) size rule (the greater of 60 m² or a share of the house), the state fast-track that gets one approved by a certifier in weeks, and what stops it. Read from the LEP text; the address check applies it to your lot.
The size rule under the LEP
Blue Mountains LEP cl 5.4(9) — the greater of 60 m² or 25% of the house’s total floor area, parking excluded. In the C4 Environmental Living zone a secondary dwelling is permitted.
The fast-track
Under the Housing SEPP a secondary dwelling is permitted wherever a house is. The complying-development route needs a lot of 450 m² and 12 m wide, a flat of up to 60 m², single storey on most lots, 3 m rear and side setbacks and a 1 m path from the street — issued by a private certifier without a DA. Smaller lots, larger flats up to the LEP percentage, and constrained land go by DA to Blue Mountains City Council. The flat stays on the house's title — it cannot be subdivided or strata-titled; that is what separates it from a duplex.
What stops it here
- Trees — a protected tree in the backyard can stop the fast-track; Blue Mountains City Council's tree controls apply before the footprint is drawn.
- Bushfire — most of the city is mapped; a BAL assessment is routine and the fast-track is usually off.
- Sewer — the main often runs across the back of the lot; building over or near it needs the water authority's approval.
- Floor area — 60 m² is internal floor space; a verandah does not count, a carport can under some readings. Confirm before designing to the limit.
More: the Blue Mountains City Council guide · duplexes in Blue Mountains · granny flat rules across NSW.
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