The complete, plain-English guide to planning, approving, and building a secondary dwelling in New South Wales. From CDC vs DA to BASIX compliance — every step explained.
Follow this process in order. Skipping steps is the single biggest cause of delays and cost blowouts.
Zoning, lot size & constraints
CDC or DA?
Architect or designer
Sustainability compliance
Lodge the application
Builder & inspections
Water, sewer, power
Final sign-off
Before spending a single dollar on plans or a builder, you must confirm your land can legally accommodate a granny flat. Many homeowners skip this step and discover problems after paying for designs.
This document (obtained from your local council for ~$53) tells you your land's zoning, any bushfire, flood, or heritage constraints, and easements on the title. It is the single most important document before you start. Do not skip this.
A drainage easement running through your backyard can make your preferred build location impossible. Always check the title documents and your 10.7 certificate before engaging a designer.
A DA (Development Application) through council allows "merit-based" assessment. It takes longer and costs more, but it can approve a granny flat that CDC cannot. Don't give up.
This is the most important decision in the whole process. The pathway you choose affects how long approval takes, how much it costs, and how much design flexibility you have.
| Factor | ✅ CDC (Complying Development) | 📋 DA (Development Application) |
|---|---|---|
| Who approves it? | Private Accredited Certifier | Local Council |
| Timeframe | 10–20 business days | 40–120 days |
| Application cost | $3,000 – $5,000 | $5,000 – $10,000+ |
| Neighbour notification | Not required | Required — neighbours can object |
| Flexibility | Rules are strict — no deviations | Merit-based — some flexibility allowed |
| Best for | Standard lots meeting all criteria | Sloped, heritage, flood or bushfire land |
| Legal framework | Housing SEPP 2021 | Local Environmental Plan (LEP) + SEPP |
If your block meets the basic criteria, CDC is almost always the better choice. The time savings alone (months vs. weeks) often justify designing your granny flat to fit the CDC rules rather than seeking DA flexibility. Talk to a private certifier early — many offer free initial consultations.
Under the Housing SEPP (CDC pathway), the maximum internal floor area for a granny flat is strictly 60m². This is measured as Gross Floor Area (GFA) from the internal face of external walls.
What is NOT counted in your 60m²:
You must apply via a DA. Some councils (e.g., Wollongong, parts of the Hunter) allow larger secondary dwellings under local LEP rules — but this is the exception, not the rule.
| Boundary | Minimum Distance | Notes |
|---|---|---|
| Front | Behind building line of main house | Average of 2 nearest neighbours or 4.5m |
| Side | 900mm | Increases as wall height exceeds 4.5m |
| Rear | 3.0m | 5.0m+ for lots over 900m² |
| From main house | 1.8m | Or 0m with fire-rated walls (60/60/60 FRL) |
Any habitable room window (bedroom or living room) overlooking a neighbour within 3 metres must be either obscure-glazed, or have a sill height of at least 1.5m above the floor.
You must provide at least 24m² of dedicated outdoor space for the granny flat occupant, with a minimum dimension of 4 metres. This cannot be shared with the main house area.
The 2026 updates have tightened definitions of "permeable" surfaces to help manage urban heat islands. A minimum percentage of your lot must remain as green/permeable space — typically 20–30% depending on your lot size. Concrete and pavers used for driveways count against this.
As of 2025/2026, secondary dwellings in NSW must meet enhanced BASIX (Building Sustainability Index) targets. These are not optional — they are mandatory for approval. A BASIX Certificate must be obtained online before lodging your CDC or DA application.
Most new granny flats now require double-glazed windows as standard. Wall and ceiling insulation must achieve the required NatHERS star rating for your climate zone.
Mandatory use of energy-efficient heat pump hot water systems (replacing gas in most cases) and LED lighting throughout. Solar-ready wiring is increasingly expected.
A minimum 2,000L–3,000L rainwater tank must be connected to the toilet and laundry. Sydney Water connection is still required for drinking water.
Because granny flats are often built in close proximity to the main house, fire separation is critical. The 2026 NCC has increased focus on non-combustible cladding materials for all external walls.
If your property is mapped as BAL-40 or Flame Zone, you cannot use the CDC pathway at all. You must apply via DA and involve the NSW Rural Fire Service in the assessment process. Check the NSW RFS Planning Portal to find your BAL rating before doing anything else.
If you plan to house an ageing parent, the NCC 2022 requires "Livable Housing" features: a step-free entry, wider doorways (820mm minimum), and reinforced bathroom walls for future grabrail installation.
Connecting your granny flat to services is often the most complex and expensive hidden cost. Stormwater in particular catches many owners off guard.
Must connect to Sydney Water (or regional equivalent) sewer main. If the main is far away, a Sewer Service Diagram (SSD) is required to show how the granny flat connects into the main house's existing pipes. Budget $3,000–$8,000+ if extensive excavation is needed.
Water must flow via gravity to the street or an approved easement. If your block slopes to the rear with no easement, you may need a pump-out system. On some lots, this single item adds $15,000–$30,000 to the build cost.
A separate sub-meter is required so the tenant can be billed for their own electricity. In 2026, many owners are installing smart meters that allow tenants to pay bills via an app. Budget $1,500–$3,000 for electrical connection and metering.
Before you finalise your design, spend $500–$1,000 on a hydraulic (plumbing/drainage) engineer's report. It will tell you exactly how your block drains and flag stormwater issues before you're committed to a design — saving potentially tens of thousands in surprises.
All costs for a compliant 60m² granny flat in NSW. These are real-world 2026 figures — not builder marketing numbers.
From first conversation to occupancy certificate. CDC pathway, standard lot.
Obtain your Section 10.7 certificate, check zoning on NSW Planning Portal, confirm lot size and width. Get a hydraulic engineer's opinion on stormwater. Decide if CDC is feasible.
Engage a draftsperson or architect. Produce a design within the 60m² and setback rules. Commission geotechnical (soil) report. Obtain BASIX certificate online.
Submit plans, BASIX certificate, and supporting reports to your private accredited certifier. Certifier issues Construction Certificate (CC) — typically within 10–20 business days if all documents are in order.
Get at least 3 quotes from licensed builders. Check their licence on Service NSW, verify insurance, and review references. Negotiate a fixed-price contract.
Site clearing → footings → slab → frame → lockup → fitout → services. Your certifier conducts mandatory inspections at key stages (footing, frame, waterproofing, final).
Certifier conducts final inspection and issues Occupation Certificate. You can now legally occupy or rent the granny flat. Connect sub-meter, arrange tenant, and start earning.
Many builders advertise 4–6 months — that's construction only. When you add design, approval, tendering, and utility connections, 8–10 months is realistic for a smooth project. DA projects typically add 2–4 months to this.
Run through every item before signing anything with a builder.
The questions we get asked most often — answered honestly.
Go directly to the official sources. Always verify current regulations here — rules change.
Lodge your CDC or DA application online, check your zoning, and track your application status.
The official NSW Government tool to generate your mandatory BASIX sustainability certificate.
The primary legislation governing granny flat approvals in NSW. The legal source of all CDC rules.
Check your Bushfire Attack Level (BAL) rating and understand construction requirements for bushfire-prone land.
Always verify your builder's licence is current and in good standing before signing any contract.
Understand CGT implications, rental income tax obligations, and the specific granny flat interest rules.
The most important first step is a free 30-minute conversation with a private certifier or town planner — before you spend anything on designs.