Sydney Rear Extension — DA vs CDC, Setbacks, Overshadowing, BASIX

A Sydney rear extension sits squarely at the intersection of two assessment pathways. Under the Housing Code of SEPP (Exempt and Complying Development Codes) 2008, a single-storey rear extension can proceed as Complying Development via a private certifier in 10-20 business days — if it meets the prescriptive standards: site area, height, setbacks, landscaped-area percentage, building-line, and BASIX. Fail any standard and the project falls out of CDC and must be lodged as a Development Application through council.

Most inner-Sydney sites (terraces, semis, small cottages in Paddington, Surry Hills, Balmain, Newtown) cannot make CDC because of the landscaped-area minimum or the side-setback rule. Most outer-suburban sites can. Knowing this before you draw is the difference between a 10-day approval and a 14-week DA assessment.

AskBaily routes your Sydney rear extension to a NSW-licensed builder who has done both CDC and DA approvals in your neighbourhood and knows which pathway fits your site.

What a Sydney rear extension involves

• Pathway. CDC (prescriptive, 10-20 days) or DA (merit, 8-16 weeks). Heritage Conservation Area typically withdraws CDC.
• Setbacks. Rear setback min 3 m on lots under 900 sqm; side setback 0.9 m under Housing Code. DCP overlays may increase these.
• Overshadowing. CDC allows up to 3 hrs mid-winter shadow on a neighbour's living areas or principal private open space. DA is merit-based.
• BASIX. Certificate required. Glazing U-value and SHGC, insulation, ventilation, water fixtures.
• Sewer. Sydney Water build-over-sewer approval where the sewer main runs under the rear yard — common in terraces and semis.
• Structural. Engineer's drawings for footings, slab, steel, and wall plate. Footing design often driven by reactive-clay soil in the Inner West.

Frequently asked questions

Can my rear extension fit under CDC? Depends on site area, landscaped area percentage, setbacks, height, floor-space ratio, and BASIX. A compact inner-Sydney site rarely fits. A freestanding home on a 600 sqm+ suburban lot often does.

Do I need a Heritage Impact Statement? If your property is on the State Heritage Register, LEP schedule-5, or a Heritage Conservation Area — yes. A heritage consultant prepares the HIS and council's heritage adviser reviews.

How much does a Sydney rear extension cost? A$180,000-A$280,000 for a modest single-storey rear addition. A$320,000-A$480,000 for a kitchen-and-living rear extension with high-spec finishes. A$550,000+ for a two-storey rear addition with structural alterations.

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