How to Choose a Granny Flat Builder: Questions, Red Flags & Checklist

TL;DR: The right granny flat builder is licensed in your state, carries both public liability and home building warranty insurance, provides a fixed-price contract with a clear inclusions list, and can show you completed projects similar to yours. Always get at least 3 quotes, compare them on a like-for-like basis, verify licensing online, speak to past clients, and never pay more than 10% deposit upfront. The biggest red flags are pressure to sign quickly, requests for cash payments, no written contract, and no insurance certificates.

Key takeaways

• Verify licensing online before any conversation. NSW: Fair Trading. QLD: QBCC. VIC: VBA. Every state has a free licence check.
• Insist on seeing insurance certificates: public liability ($10-20 million), home building compensation/warranty, and builders all-risk during construction.
• Get a fixed-price contract, not a cost-plus estimate. Fixed-price protects you from overruns.
• Compare 3+ quotes on a like-for-like basis using the checklist in this guide.
• Never pay more than 10% deposit and never pay ahead of completed work stages.
• Walk away from builders who pressure you to sign on the spot, request cash, avoid written contracts, or cannot show past work.
• Use the grannyflatcost.com calculator to get a realistic budget estimate before approaching builders, so you can evaluate quotes with confidence.

What to look for in a granny flat builder

1. Correct state licensing

Builder licensing is state-based in Australia. A licence in one state does not authorise work in another. Here is how to verify:

State	Authority	Check online
NSW	NSW Fair Trading	fairtrading.nsw.gov.au
QLD	QBCC (Queensland Building and Construction Commission)	qbcc.qld.gov.au
VIC	VBA (Victorian Building Authority)	vba.vic.gov.au
WA	Building Services Board	commerce.wa.gov.au
SA	Consumer and Business Services	cbs.sa.gov.au
TAS	Consumer Building & Occupational Services	cbos.tas.gov.au
ACT	ACT Construction Occupations Registrar	accesscbr.act.gov.au

In Queensland, the QBCC licence requires a Diploma of Building and Construction, four years of supervised experience, and passing a financial assessment. It is one of the more rigorous licensing systems in Australia.

In Victoria, only VBA-registered builders can legally construct granny flats. Hiring an unregistered builder voids your domestic building insurance and exposes you to $50,000+ in liability if defects emerge.

Always check the builder’s licence number on the relevant authority’s website. It takes 30 seconds and is the single most important step you can take.

2. Insurance coverage

A properly insured builder protects you during and after the build. There are three types of insurance to verify.

Public liability insurance ($10-20 million) covers injury or damage to third parties (your property, neighbours) during construction. Every legitimate builder carries this.

Home building compensation / warranty insurance — known as HBCF in NSW, domestic building insurance in VIC, and statutory warranty in QLD — protects you if the builder goes bankrupt, disappears or fails to fix defects. In most states, it is legally required for residential work above $20,000.

Builders all-risk insurance covers the structure under construction against fire, storm, theft and accidental damage. This should be in place from day one of construction.

Ask for copies of all three certificates. If a builder hesitates or says their insurance “is being renewed,” move on.

3. Granny flat specialisation

Building a granny flat is not the same as building a house extension or a new home. Granny flat specialists understand compact space design, council approval pathways for secondary dwellings, tight-access site logistics, setback and site coverage requirements, and how to make 60-80 sqm genuinely livable.

A builder who primarily does house extensions may quote competitively but lack the knowledge that prevents costly design mistakes and approval delays.

4. Portfolio of completed work

Established builders will readily show photos, videos and even physical display homes. Ask to see at least 5 completed granny flats of similar size and specification to yours, before-and-after photos of the building site (not just the finished product), and a mix of project types to demonstrate range.

If the builder cannot show completed work, they are either new to granny flats or reluctant to share their track record. Neither is a good sign.

5. Verifiable references

Ask for contact details of at least 3 past clients from the last 12 months. When you call them, ask:

• Was the project completed on time? If not, what caused the delay?
• Was the final cost the same as the quoted price? Were there any variations?
• How was communication during the build? Were you kept informed of progress?
• Were there any defects after completion? How quickly were they resolved?
• Would you use this builder again?

Pay attention to consistency across references. If all three mention the same strength or weakness, that is a reliable signal.

12 questions to ask before signing

These questions help you compare builders on substance, not salesmanship.

Pricing and scope

1. Is this a fixed-price contract or a cost-plus estimate? Fixed-price is strongly preferred. Cost-plus means the final price can be significantly higher than the initial estimate.

2. What is included in the price? Get a detailed inclusions list covering: design and drafting, engineering, council/certifier fees, site preparation, slab/stumps, full build, kitchen and bathroom fixtures, flooring, painting, electrical and plumbing, utility connections, landscaping, driveway, and clean-up. Anything not on this list is an exclusion you will pay extra for.

3. What are the provisional sum and prime cost items? Provisional sums are estimates for work where the cost is unknown (e.g., excavation on rocky ground). Prime cost items are allowances for fixtures you have not yet selected. Both can increase your final bill. Minimise them wherever possible.

4. Are council fees and infrastructure charges included? Some builders include council application fees in their price; others treat them as extras. In areas like Logan (QLD), the $23,000 infrastructure charge alone can blow an unprepared budget.

Timeline and process

5. What is the expected timeline from contract signing to handover? A standard 60 sqm granny flat typically takes 12-16 weeks for site-built, or 8-12 weeks for prefab. Get the timeline in writing.

6. What happens if the build runs over time? Ask about liquidated damages or any contractual consequence for late completion. Some contracts include a daily penalty for overruns; others do not.

7. How many projects are you currently managing? A builder running too many projects simultaneously will spread their team thin, leading to delays on your build.

Quality and warranty

8. What warranty do you provide? The minimum acceptable structural warranty is 6 years (mandated by most states). Many reputable builders offer 25-year structural warranties. Non-structural defect warranties are typically 2 years.

9. Who are your regular subcontractors? Consistent subcontractor relationships indicate a well-run operation. Builders who use different trades on every job may have quality control issues.

10. Can I inspect the work at each progress payment stage? You should always inspect before releasing a progress payment. A good builder welcomes this.

Communication

11. Who will be my main point of contact during the build? You should have a dedicated project manager or site supervisor, not just a sales rep.

12. How often will I receive progress updates? Weekly written updates with photos are the standard you should expect.

Red flags: when to walk away

Immediate deal-breakers

• No written contract. Every residential building project requires a written contract. Verbal agreements have no legal standing.
• Requests for cash payments. This avoids the paper trail and likely means no GST is being charged (tax fraud) and no insurance is in place.
• No licence or expired licence. Check the date and scope. A licence for “minor works” does not cover a full granny flat build.
• No insurance certificates provided. “Trust me, I’m covered” is not proof.
• Deposit demand above 10%. In NSW and VIC, the legal maximum deposit is 10% of the contract price. Any builder asking for more is breaking the law.

Serious warning signs

• Pressure to sign quickly. “This price is only valid today” or “I have another client interested” are sales tactics, not signs of a reputable business.
• Vague or missing inclusions list. If the quote does not specify exactly what is included, you will be paying extra for every item that surfaces during the build.
• No portfolio or references. A builder with nothing to show has either not built granny flats before or has a track record they want to hide.
• Unusually low quotes. A quote that is 20-30% below competitors is either missing scope items, using cheap materials, or from an unlicensed operator. The lowest price is rarely the best value.
• Poor communication before signing. If a builder is slow to respond or dismissive of your questions during the sales process, the communication will only get worse once construction starts.
• No ABN or GST registration. Check the Australian Business Register at abr.business.gov.au. A legitimate building company will have an active ABN and be registered for GST.

Builder types: which is right for you?

Large granny flat companies

National or state-wide firms with display homes, sales teams and standardised product ranges.

Pros: established processes, pre-approved designs for faster approvals, dedicated project managers, strong warranty backing. Cons: less flexibility for custom designs, potentially higher overhead costs passed to you, may use subcontractors you do not choose. Best for homeowners wanting a streamlined, low-risk process with predictable outcomes.

Small specialist builders

Local operators building 5-20 granny flats per year, often owner-operated.

Pros: personal attention from the owner/builder, more design flexibility, often better value due to lower overhead, strong local council knowledge. Cons: smaller teams mean delays if a key person is sick or stretched across projects, may have less formal processes, and warranty depends on business continuity. Best for homeowners wanting a personalised build experience and local expertise.

Owner-builder

You act as the builder, hiring and coordinating all trades yourself.

Pros: potential 20-30% cost saving by eliminating builder margin, full control over every decision. Cons: requires significant time (essentially a part-time job for 6+ months), owner-builder permits required in all states (NSW: $219, VIC: $110, QLD: $462), financing is harder (most lenders require a licensed builder), there is no builder warranty, and some states restrict resale (VIC: cannot sell for 6 months after completion).

Best for experienced DIYers or people with construction industry knowledge who have the time to manage the project full-time.

How to compare quotes: like-for-like checklist

When you have 3+ quotes, use this checklist to compare them fairly. Builders often include different items, making a straight price comparison misleading.

Item	Builder A	Builder B	Builder C
Design/drafting fees
Engineering
Council/certifier fees
Site clearing
Slab or stumps
Frame and roof
External cladding
Windows and doors
Electrical (how many points?)
Plumbing
Kitchen (brand/specs)
Bathroom (brand/specs)
Flooring (type/brand)
Painting (coats/brand)
Utility connections
Air conditioning
Landscaping/paths
Fencing
Clean-up and waste removal
Provisional sum items
Prime cost allowances
TOTAL

Fill in each row for each builder. The builder with the lowest total is not necessarily the best choice. Look at which builder includes the most items in their fixed price and has the fewest provisional and prime cost items.

Understanding your contract

Before signing, review these sections of your building contract carefully.

Contract price and variations

The contract must state the total fixed price including GST. Variations (changes to the agreed scope) should require your written approval before any additional work begins. Never accept a contract that allows the builder to make variations without your consent.

Progress payment schedule

Progress payments should be tied to completed stages of work, not calendar dates. A typical schedule looks like this:

Stage	Percentage	Description
Deposit	5-10%	On contract signing
Base/slab	15%	Foundations complete
Frame	20%	Structural frame erected
Lock-up	20%	Roof, windows and doors installed
Fit-out	25%	Internal trades complete (plumbing, electrical, kitchen, bathroom)
Completion	10%	Final clean, practical completion, handover

Never pay ahead of completed work. Each payment should only be released after you inspect and confirm the stage is complete. NSW and VIC legally limit the deposit to 10% of the contract price. QLD does not have a statutory cap, but 10% is the industry standard.

Defects liability period

After practical completion, there is typically a 13-week defects liability period during which the builder must rectify any defects you identify at no cost. Document everything in writing with photos.

Dispute resolution

The contract should specify a dispute resolution process (mediation, then tribunal). In NSW, disputes go to NSW Fair Trading and then NCAT. In VIC, VCAT. In QLD, QBCC handles complaints and disputes.

Getting the best outcome

1. Know your budget before approaching builders. Use the grannyflatcost.com calculator to establish a realistic cost range for your area, build type and specification.
2. Get 3-5 quotes. The more quotes you compare, the better you understand the market rate for your project.
3. Visit completed builds. Photos are good; walking through a finished granny flat is better. You will see the quality of finishes and details that photos cannot convey.
4. Read the contract in full. Do not rely on the builder’s verbal explanations. Everything that matters should be in writing.
5. Check the builder’s QBCC/Fair Trading/VBA history. Look for past complaints, disciplinary actions or financial issues on the relevant state authority’s website.
6. Keep 10% of the contract price as the final payment. This gives the builder a financial incentive to complete the final details and rectify defects before handover.
7. Document everything. Keep copies of all quotes, contracts, variation orders, emails, progress photos and payment receipts. If a dispute arises, documentation is your best protection.