The short answer
Most modest NSW decks need no approval at all: up to 25m², under 1m high, attached, behind the building line and clear of boundary setbacks = exempt development. Bigger or higher = CDC (private certifier, weeks, a certifier's fee). Complicated land = DA.
| Your deck | Path | Approval costs & time |
|---|---|---|
| ≤25m², <1m high, attached, setbacks met | Exempt — no approval | None — build when ready |
| Larger or elevated, standard block | CDC via private certifier | Certifier fee, typically 2–4 weeks |
| Heritage / bushfire / foreshore / easements | DA via council | Council DA fees, and months not weeks |
The honest fine print: exempt-development standards have more conditions than fit in a table (zone, lot size, total area of structures, drainage), and heritage conservation areas — common around Castlecrag, Mosman and parts of Northbridge — change answers. Treat this guide as the map, and get the site-specific answer confirmed before ordering timber. Timing note: a CDC runs happily in parallel with quoting and material lead times, so "needs approval" rarely delays a well-planned build by much.
We give every deck quote its approval answer in writing — exempt, CDC or DA — before you commit. See our deck building service or ask below with a photo of the space.
Why the 1m line matters twice
One metre is where two rulebooks meet: above it, a deck usually exits exempt developmentand enters balustrade territory (required at 1m+ falls under building standards). That's not bureaucratic coincidence — elevation is where decks hurt people, which is why elevated designs get engineered posts, bracing and compliant balustrades whatever the approval path. On the Lower North Shore's sloping blocks, "low deck at the door, high deck at the far rail" is common — the highest point sets the rules.
The CDC route, demystified
A Complying Development Certificate sounds bureaucratic and is actually the fast lane: a private certifier checks the design against the complying-development standards and issues approval without a council DA. You'll need drawings and site details — which a builder who does this weekly simply produces — then certification, build, and final inspection. The certifier's fee and the drawings are the main approval costs, and the few weeks of lead time can overlap with the quoting and material-ordering you'd do anyway.
The exempt checklist, spelled out
"Exempt development" is a conjunction of conditions — miss one and the deck isn't exempt. The ones that decide most Lower North Shore cases:
- Area: the deck itself ≤25m² — and councils also cap the totalarea of such structures on a lot, so an existing shed or patio counts against you.
- Height: no part more than 1m above existing ground level — measured at the lowest point, which is what catches sloping blocks.
- Position: attached to the dwelling, behind the building line, and meeting side/rear setbacks (commonly 900mm).
- Land: not heritage-conservation, foreshore, or otherwise mapped land — the constraint that quietly applies across parts of Castlecrag, Mosman and Northbridge.
- Drainage and structure: stormwater handled lawfully, construction to standard — exemption from approval is never exemption from building properly.
Score five ticks and you're building next month. Any misses simply route you to CDC — a detour of weeks, not a refusal — and your builder should be the one doing this scoring, in writing, before a dollar changes hands.
Building it right is the other half
Approval says a deck may exist; construction standards decide whether it should. Footings, spans, fixings, ledger flashing and balustrades all carry standards regardless of approval path — an exempt deck built badly is still a bad deck, just a legal one. Ourdeck building service covers what proper construction looks like and how we build to it.
And if you've inherited an unapproved deck with the house: don't panic, don't ignore it either. Sound structures can often be regularised through a certifier (a building information certificate is the usual instrument), and unsound ones are better discovered by your builder than by your insurer. We inspect and give the straight answer — keep, regularise, or rebuild — the same way we would for a deck we were quoting new.