Guide
Renovating and extending in NSW
Four possible pathways, and the one you're on is decided by whether the work adds floor area.
Start with one question
Does the work add gross floor area?
If it doesn't — internal reconfiguration, a new bathroom, re-cladding, replacing windows, an attic conversion inside the existing roof — you are in the Housing Alterations Code, and a lot of it is straightforward complying development.
If it does — a rear extension, a first-floor addition, an alfresco under roof — the addition is assessed as attached development under the Housing Code, and here is the part that surprises people: the existing house and the addition together have to satisfy the Housing Code standards. You are not being assessed on what you're adding. You are being assessed on the total.
The calculation that decides most extensions
The Housing Code caps the gross floor area of all buildings on the lot. Worked through on a common case:
- Lot area 600 m² → floor area cap 335 m²
- Existing house 280 m², existing garage 40 m² → 320 m² already used
- Headroom: 15 m²
Fifteen square metres is a bathroom and a hallway. It is not the extension anyone had in mind, and this arithmetic is why a great many renovation projects change shape in the first week rather than the fifth month.
Working out the existing floor area properly — from the title and a measure, not from a real estate listing — is the first thing worth doing. It is cheap, and it is the number everything else depends on.
The other constraints
Height — 8.5 m, which is rarely binding on a two-storey addition but occasionally is on a sloping block where it's measured from existing ground level.
Side and rear setbacks — formula-based, and they tighten as the building gets taller. This is where first-floor additions fail. A ground floor at 900 mm from the boundary may be perfectly legal while a storey above it is not.
External work under the Alterations Code carries its own conditions: at least 3 m from a side or rear boundary and behind the building line, and only to the first three storeys.
Attic dormers have specific limits — no wider than 1.3 m, set in at least 500 mm, at least 200 mm below the ridge, and no more than 4 m² total to the side and rear. A design wanting a wider dormer is a DA, and often a better project as one.
Heritage is the usual blocker for external work, and the most commonly unknown constraint.
Where to go next
- Alterations and additions — the full pathway table and the code conditions
- CDC or DA — which route applies and what closes the fast one
- What it costs — the estimator has a second-storey option, which carries hidden items a per-square-metre rate never includes
- If work was already done without approval
Common questions
Do I need approval to renovate?
It depends entirely on what the work is. Minor internal alterations and small external work can be exempt development needing no approval at all. Larger internal work and external alterations that add no floor area generally run under the Housing Alterations Code as complying development. Anything that adds floor area is assessed under the Housing Code, and heritage or a failed standard sends it to a development application.
What is the difference between an alteration and an addition?
Whether it adds gross floor area. That single question decides which code applies, and it is not the same as whether the job feels big — moving a wall and adding a room are governed by different instruments.
How much can I extend?
The Housing Code caps the floor area of all buildings on the lot, not the addition. So the headroom is the cap for your lot size minus what is already there, including the garage and any shed. On a block with a large existing house that number can be very small.
Can I add a second storey as complying development?
Sometimes, but the side setbacks are where it usually fails. Setbacks are formula-based and tighten as the building gets taller, so a ground floor sitting legally at 900 mm may not be able to carry a storey above it.
What if my house is in a heritage conservation area?
External alterations in a conservation area are generally excluded from the Housing Alterations Code, which means a development application with a heritage impact statement. Internal-only work may still be exempt or complying development. Many owners do not know they are in a conservation area — it is worth checking before budgeting.
Do I need approval for a deck, a pergola or a carport?
Often these fall within exempt development if they stay inside the size, height and setback limits, and within complying development if they do not. The limits are specific, and going slightly over any of them changes the pathway.
General information about NSW planning, current at September 2026. Not advice on a particular site — the instruments are amended often and councils vary them locally.
Thinking about extending?
Send us the address and what you're planning. We'll tell you the pathway and the headroom you have.