Residential design
Alterations and additions
The most constrained work we do. An existing house has already used part of the envelope, and what's left is what you get.
Renovation work in NSW doesn't have one approval pathway — it has four, and which one applies is decided by exactly what you're doing rather than by how big the job feels. Moving a wall and adding a room are governed by different codes.
The distinction that drives everything: does the work add gross floor area? If it doesn't, you are in the Housing Alterations Code. If it does, the addition is assessed as attached development under the Housing Code, and the existing house and the addition together have to satisfy the Housing Code standards. That second point is where renovations run aground.
Which pathway applies
| The work | Pathway | Instrument |
|---|---|---|
| Minor internal work, and minor external work inside the exempt limits | Exempt development | Codes SEPP Part 2 |
| Internal alterations, and external alterations that don’t add floor area | CDC — Housing Alterations Code | Codes SEPP Part 4 |
| Attic conversion within the existing roof | CDC — Housing Alterations Code | cl 4.5–4.6 |
| An addition that increases gross floor area — a rear extension, a first-floor addition | CDC — Housing Code, as attached development | Codes SEPP Part 3 |
| Anything in a heritage conservation area or on a heritage item, or failing a code standard | Development application | LEP + DCP, s4.15 |
The Housing Alterations Code, in the conditions that bite
Part 4 covers alterations that don't add floor area. The conditions that most often decide whether a job qualifies:
- No change to the building's BCA classification (cl 4.4B(1)(a))
- No effect on fire-resisting components or on egress (cl 4.4B(1)(d)–(e))
- External work must be at least 3 m from a side or rear boundary and behind the building line (cl 4.4B(1)(g)–(h)), with an exception for an access ramp
- External work only to the first three storeys (cl 4.4B(3))
- Height within the EPI limit, or no higher than the uppermost habitable floor (cl 4.4B(1)(f))
- Alterations to an existing balcony or deck can't increase its floor area or level (cl 4.4B(4))
Attic conversions
Converting the existing roof space is CDC under clauses 4.5 and 4.6, and the dormer rules are specific: a dormer no wider than 1.3 m, set in at least 500 mm, at least 200 mm below the ridge, and a total area of no more than 4 m² to the side and rear. A design that wants a wider dormer is a DA, and it is usually a better project as a DA.
Additions: the floor area cap is the real constraint
Where an addition increases gross floor area, the Housing Code applies and the cap is on all buildings on the lot, not on the addition. On a 600 m² lot the cap is 335 m² (cl 3.9). If the existing house is 280 m² and there's a 40 m² garage, the headroom is 15 m² — which is a bathroom, not an extension.
This is the calculation that decides most renovation projects, and it is almost never the one people start with. Working out the existing GFA properly, from the title and a measure rather than from a real estate listing, is the first thing we do.
The other binding constraints: 8.5 m maximum height (cl 3.8), and the side and rear setbacks (cl 3.10), which are formula-based and tighten as the building gets taller. A first-floor addition is where side setbacks usually fail — the ground floor may sit at 900 mm quite legally while a second storey above it cannot.
Heritage, which is the usual blocker
External alterations in a heritage conservation area are generally excluded from the Alterations Code. The exception at clause 1.19(1)(a) saves only detached outbuildings, detached development other than a studio, and pools — which is to say, not your extension.
In practice a heritage conservation area means external work goes to a DA with a heritage impact statement. Internal-only work may still be exempt or complying development, which is worth knowing because it changes the sequencing of a project considerably.
A lot of owners don't know they're in a conservation area. It is not always obvious from the street and it isn't always old houses. Checking it is thirty seconds of work and it changes the entire budget.
What we do
Establish the existing gross floor area properly, test the work against the right code, tell you the headroom you have, and design inside it — or tell you the addition you want needs a DA and what that costs in time.
Where the answer is that the block is effectively full, we say so. It's an unwelcome answer but it's cheaper at week one than at month five.
Our fees for alterations and additions start at $4,800 + GST via DA. The cost estimator has a second-storey option, which carries hidden items — roof removal, stair, BASIX retrofit — that a per-square-metre rate never includes.
Figures are the state baseline under the Codes SEPP. Councils vary the codes for their own areas through Schedule 3 and the SEPP is amended often — everything here needs confirming against your address and the in-force version.
Thinking about extending?
Send us the address and what you're planning. We'll tell you the pathway and the floor area you have left.