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Owner guide · knockdown rebuild

Knockdown rebuild mistakes to avoid in Sydney: 12 checks (2026)

The mistakes that cost owners the most time and money in a Sydney knockdown rebuild, and what to do instead. Each check cites the NSW Government rule or the dated source behind it.

By XLGUpdated: 2026-10-28Every rule and figure is dated and sourcedPublished by AUD Build

Short answer

The most expensive knockdown rebuild mistakes are demolishing or moving out before the new home is approved, assuming a CDC without checking the lot, leaving asbestos, site costs, rent and council charges out of the budget, and paying a deposit before HBC insurance is in place. Check the lot with a section 10.7 planning certificate, get the survey, soil and asbestos reports before you compare fixed prices, and sign a large job contract only after the licence and HBC certificate check out.

1. Demolishing before the new home is approved

The mistake: Booking demolition, or moving out, before the approval for the new home is granted.

What to do instead: The Planning Portal says you cannot demolish your existing house until approval for your new home has been granted, and your council may require a security bond against damage to council property during demolition. Sequence the job as approval, then disconnections, then demolition. [1]

2. Assuming your block can use a CDC

The mistake: Designing for a fast complying development certificate (CDC) without checking whether the lot qualifies.

What to do instead: Complying development is excluded on heritage items, heritage conservation areas and other excluded land. Order a section 10.7 planning certificate and check the codes before design. If you need a DA instead, average council assessment times across Greater Sydney ranged from 41 to 122 days in the September 2026 league table. [3] [4]

3. Leaving asbestos to chance

The mistake: Getting a demolition price before anyone has checked the house for asbestos.

What to do instead: Friable asbestos, or more than 10 m² of bonded asbestos, needs a licensed removalist and a clearance inspection before the site reopens. Published allowances for removal run from about A$2,500 to A$28,000. Get an asbestos survey before you compare demolition quotes. [5] [16]

4. Forgetting the neighbour and council notices

The mistake: Starting demolition without the required notice periods.

What to do instead: In metropolitan areas, neighbours within 20 m need at least 7 days’ written notice before demolition, and council must be notified at least 2 days before work starts. Build these days into the programme. [2] [6]

5. Comparing quotes that measure different things

The mistake: Choosing the lowest total when builders used different floor-area definitions and inclusions.

What to do instead: Some builders price habitable floor area, others include garages and alfresco. Compare every quote on the same drawings, the same floor-area definition and the same inclusions list. [16]

6. Ignoring site costs until after the contract

The mistake: Signing a fixed price before the survey and soil report are done.

What to do instead: Published ranges show slope, retaining and benching at A$20,000–A$80,000, rock excavation at A$15,000–A$50,000 and engineered footings on reactive clay at A$10,000–A$40,000. Survey, geotechnical, BASIX and structural reports (about A$8,000–A$14,000) come first. [16]

7. Leaving rent and council charges out of the budget

The mistake: Budgeting only the builder’s price.

What to do instead: Most published all-in figures exclude council contributions and temporary rent. A year renting at the Greater Sydney median of A$800 a week is about A$41,600, and the Department confirms a section 7.12 levy can be charged when a house is knocked down and replaced, usually no more than 1% of cost. [7] [8]

8. Paying a deposit before HBC insurance is in place

The mistake: Paying a deposit on a contract over A$20,000 before seeing the home building compensation (HBC) certificate.

What to do instead: HBC cover must be in place before you pay a deposit on residential building work over A$20,000. Check the certificate on the official HBC Check, and remember the deposit cannot exceed 10%. [9] [10] [11]

9. Signing without a proper large-job contract

The mistake: Starting on a quote or a short letter of agreement.

What to do instead: Work over A$20,000 needs a large job contract that includes a cooling-off statement of five clear business days, and progress payments should match work actually done. [11]

10. Not checking the licence of the company you sign with

The mistake: Trusting a brand name without checking the licence holder.

What to do instead: Check the contractor licence on Verify NSW (via Service NSW) and make sure the licence holder is the company named on your contract. [12]

11. Forgetting the levy and the energy rules

The mistake: Not allowing for state charges and current energy standards in the design and budget.

What to do instead: The long service levy (0.25% of building work of A$250,000 or more) must be paid before the construction certificate or CDC is released, and new homes have had to meet 7-star NatHERS thermal performance under BASIX since 1 October 2023. [13] [14]

12. Underestimating how long you will be out of the house

The mistake: Signing a 6-month lease for the build.

What to do instead: AUD Build’s timeline guide puts a Sydney knockdown rebuild at about 9–16 months with a CDC and 12–18+ months with a DA, and the ABS found the average gap between a demolition approval and the related building approval was 5.6 months in 2024/25. [17] [15]

How AUD Build handles these checks

The written proposal states whether demolition, permits, utility disconnections and hazardous-material work are included or arranged separately, and demolition is tendered with competing quotes.
Design by AUD Design includes the DA or CDC approval drawings, so the approval route and its constraints are settled during design; design decides how a home is built and what it costs.
Materials come from AUD Build’s own supply chain platform, www.audbuild.net, and AUD Build clients can log in to check the material unit prices in their quote.
NSW Builder Licence 475778C; HBC certificates and planning records are on the third-party evidence page.

Questions

What is the most common knockdown rebuild mistake?

Leaving costs out of the budget. Most published all-in figures exclude council contributions and rent while you build, and asbestos, rock and retaining are often provisional sums. Get the survey, soil and asbestos reports before you compare fixed prices.

Can I demolish my house before the new home is approved?

No. The NSW Planning Portal says you cannot demolish your existing house until approval for your new home has been granted.

When do I need HBC insurance?

Before you pay a deposit on residential building work over A$20,000. Check the certificate on the official HBC Check.

How long will I be out of my house?

About 9–16 months with a CDC and 12–18+ months with a DA, according to AUD Build’s 2026 timeline guide.