Residential design
Granny flats and secondary dwellings
A self-contained dwelling on the same lot as the house. Its own chapter of the Housing SEPP, its own standards, and a CDC pathway that a surprising number of sites qualify for.
A secondary dwelling is a self-contained dwelling on the same lot as a principal dwelling. It is governed by Chapter 3 of State Environmental Planning Policy (Housing) 2021, with the complying development pathway in Schedule 1.
The point most people miss: a secondary dwelling is not a dwelling house for the purposes of the Housing Code (Codes SEPP cl 3.1(4)). The figures that apply to a new house do not apply here. Different lot requirements, different setbacks, and a floor area cap the house doesn't have.
It is permitted with consent on a lot in a residential zone where a dwelling house is permissible under another environmental planning instrument. If a house isn't permissible in the zone, a granny flat generally isn't either.
The standards that decide it
The 60 m² figure is the state default, not the answer. Many councils permit more in their LEP — commonly up to 100 m² — and checking that is one of the first things worth doing, because it is often the difference between a one-bedroom and a two-bedroom result. We never quote 60 m² without reading the LEP.
Minimum primary road frontage — Schedule 1 cl 2(1)(b)
Measured at the building line, for a lot that isn't a battle-axe:
| Lot area | Minimum frontage |
|---|---|
| 450 – 900 m² | 12 m |
| > 900 – 1,500 m² | 15 m |
| > 1,500 m² | 18 m |
A battle-axe lot needs an access laneway at least 3 m wide and a building area of at least 12 m × 12 m excluding the laneway (cl 2(1)(c)).
Side and rear setbacks — Schedule 1 cl 9 and cl 10
Side setback
| Lot area | Minimum |
|---|---|
| > 450 – 900 m² | 0.9 m |
| > 900 – 1,500 m² | 1.5 m |
| > 1,500 m² | 2.5 m |
Plus 25% of any building height above 3.8 m, for walls or structures over that height.
Rear setback
| Lot area | Minimum |
|---|---|
| 450 – 900 m² | 3 m |
| > 900 – 1,500 m² | 5 m |
| > 1,500 m² | 10 m |
Plus 3 × (building height − 3.8 m) where higher. It doesn't apply to a three-boundary or battle-axe lot, and a building line may abut a rear laneway for up to half its length.
On a corner lot, the secondary road setback is 2 m (450–600 m²), 3 m (600–1,500 m²) or 5 m (over 1,500 m²) — cl 7(3). A classified road takes the LEP figure for a dwelling house, otherwise 9 m (cl 8). A parallel road, 3 m (cl 7(2)).
Amenity, and the parking rule people get wrong
- Principal private open space — more than 24 m², more than 4 m wide, at a gradient no steeper than 1:50. It can be shared with the principal dwelling and it can be a balcony or deck (cl 17).
- Landscaped area — to the Schedule's standard, with a minimum dimension of 2.5 m (cl 16).
- Car parking — the number of on-site spaces must be the same as before the development (cl 53(2)(b)). No extra space is required for the granny flat. What you cannot do is delete the house's existing parking to make room for it, which is exactly what a lot of concept plans quietly do.
What closes the CDC pathway
Eligibility is cumulative — one failed test and it's a development application instead. The usual causes:
- Frontage under the Schedule 1 minimum, which is the single most common failure
- A lot under about 450 m², where the setback tables don't operate
- A heritage item, or land in an environmentally sensitive area
- Flood or bushfire constraints beyond what the Codes allow. Note that for a secondary dwelling on a flood control lot, the flood refuge level is the probable maximum flood level, not the 1% AEP — a materially higher bar that catches people out
- A rear setback that can't be achieved once the existing house and its open space are accounted for
A DA is still available where the CDC isn't. A granny flat on a 400 m² lot or a narrow frontage can be approved on merit — it just takes the longer route. That is a real option and worth pricing rather than abandoning.
What we do
We test the lot against Schedule 1 and the LEP, tell you the floor area you're actually allowed rather than the one you've read about, design the dwelling to fit the buildable band that's left, and document it for the certifier or the council.
Our fees are $4,300 + GST for a secondary dwelling CDC and $5,400 + GST via DA. The cost estimator covers the build, and note the service connections line — a granny flat usually needs separate metering, which runs materially higher than a normal connection.
Figures on this page are the Housing SEPP state baseline. LEP floor-area allowances and lot minimums vary by council and the SEPP is amended often — every figure needs confirming against your address and the in-force version.
Will a granny flat fit on your block?
Send us the address. We'll test it against the standards and tell you the size you can actually build.