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Insurance for Design-and-Build Contracts: When Builders Take on Design Risk

·15 min read

Insurance for Design-and-Build Contracts: When Builders Take on Design Risk

You’re three months into a $2.8 million townhouse development in Sydney’s inner west. The structural engineer’s report arrives with a red flag: the architect’s load-bearing wall calculations are off by 12%. The architect points to your contract—you signed a design-and-build agreement. Now the liability for redesign, council resubmission, and a six-week program delay lands squarely on your company’s balance sheet. Your professional indemnity policy? It excludes design work because you’re a builder, not a consultant.

This scenario plays out more often than most builders admit. In 2025, the Australian Construction Industry Forum reported that design-and-build contracts accounted for 43% of all private sector commercial projects nationally, up from 31% in 2020. But many registered builders still carry insurance structured for construct-only work. That mismatch is a ticking liability.

Let’s break down exactly what insurance you need when you take on design risk—and what happens if you get it wrong.

The Design-and-Build Insurance Gap: Why Standard Builder Policies Fall Short

A standard public liability and contract works policy covers physical damage, injury on site, and defective workmanship in a narrow sense. It does not cover financial loss arising from design errors—even if those errors are made by your in-house team or a subconsultant you engaged.

The distinction is critical. When you hold a design-and-build contract, you are legally responsible for the design’s fitness for purpose, regardless of who produced it. If the architect you hired makes an error that leads to structural failure or code non-compliance, your client’s claim will name you as the principal contractor. Your public liability insurer may deny coverage because the loss is professional in nature, not accidental.

According to the Insurance Council of Australia’s 2025 Construction Professional Liability Report, design-related claims now represent 37% of all builder liability notifications above $100,000—up from 22% in 2020. The average design-error claim in New South Wales alone sits at $187,000, with legal costs adding another $45,000 to $80,000.

What Policies Do You Actually Need for Design-and-Build Work?

For any registered builder entering a design-and-build contract, you need three distinct insurance layers. Skipping any one creates a coverage gap that could bankrupt a small to medium enterprise.

Professional Indemnity Insurance for Design Risk

Professional indemnity (PI) insurance is the primary policy covering design errors, omissions, and negligent advice. For design-and-build contractors, this policy must extend to cover:

Premium ranges for builder-specific PI in 2026 run from $6,500 to $28,000 annually for policies with $1 million to $5 million in cover, depending on project value, design complexity, and claims history. For a typical $2 million design-and-build residential project, expect $8,500 to $14,000 per year if you have no prior claims.

The Queensland Building and Construction Commission (QBCC) now requires PI cover for all builders holding a design-and-build licence classification. As of 1 July 2025, QBCC minimum PI is $1 million per claim and $2 million in aggregate. New South Wales Fair Trading does not mandate PI for builders, but if your contract includes design, your client’s solicitor will almost certainly require it in the deed.

Contract Works Insurance with Design Extension

Your standard contract works policy covers physical loss or damage to the works during construction. But standard policies exclude “design defect” or “faulty design” as a cause of loss. If a design error causes a wall to collapse during construction, the policy may deny the claim.

The fix is a design extension clause. This endorsement covers physical damage to the works resulting from a design error—but not the cost of redesigning or replacing the defective design itself. The redesign cost falls under your PI policy.

Premium for contract works with a design extension typically adds 12% to 18% to the base policy cost. For a $3 million project, base contract works might run $18,000 to $25,000; the design extension adds roughly $2,500 to $4,500.

Public Liability Insurance with Professional Risk Endorsement

Public liability covers third-party injury or property damage. For design-and-build work, your liability policy needs a professional risk endorsement to cover scenarios where a design error leads to injury off-site—for example, a balcony designed with insufficient load capacity that collapses onto a pedestrian.

Standard public liability excludes professional advice. Without the endorsement, you have no coverage for injury caused by design negligence. The endorsement typically adds 8% to 12% to the base premium. Expect $3,000 to $6,000 extra per year for a $20 million aggregate policy.

State-by-State Regulatory Requirements for Design-and-Build Insurance in 2026

Each state’s building regulator has different requirements. Here is the current landscape.

New South Wales

NSW Fair Trading does not mandate PI insurance for builders. However, the Design and Building Practitioners Act 2020 imposes a duty of care on builders to exercise reasonable skill and care. For design-and-build contracts, this duty extends to the design. If you breach it, you face unlimited liability for economic loss.

The NSW Building Commissioner’s office has indicated that from 1 January 2027, all builders entering design-and-build contracts on residential apartment buildings above three storeys must hold PI cover of at least $2 million. This is not yet law, but it is the stated direction.

Victoria

The Victorian Building Authority (VBA) requires all registered builders who offer design services to hold professional indemnity insurance. For domestic builders, minimum cover is $1 million per claim and $2 million aggregate. For commercial builders, the VBA recommends $2 million per claim, though it is not a statutory minimum.

From 1 July 2026, the VBA will introduce mandatory PI for all builders supervising or performing design work on Class 1 and Class 2 buildings under the Domestic Building Contracts Act. The minimum limit will be $2 million per claim.

Queensland

QBCC has the strictest requirements. If you hold a design-and-build licence (classifications like “Builder – Design and Construct” or “Builder – Low Rise with Design”), you must maintain:

QBCC conducts random audits of PI certificates. In 2025, they issued 47 compliance notices to builders who could not produce current PI policies. Fines range from $2,300 to $23,000 per offence.

Western Australia

Building and Energy WA requires builders offering design services to hold PI cover of at least $1 million per claim. This applies to registered builders only—owner-builders are exempt. The requirement is enforced through the Building Services (Registration) Act 2011.

South Australia and Tasmania

Neither state currently mandates PI for builders in design-and-build contracts, but both regulators recommend it. The South Australian Housing Authority’s standard building contract templates now include a clause requiring the builder to hold PI cover if design is included.

Australian Capital Territory

ACT Planning and Land Authority requires PI cover for builders who prepare or coordinate designs for multi-unit developments. Minimum limit is $1 million per claim.

Northern Territory

No statutory PI requirement, but the NT Building Practitioners Board recommends it for any contract where the builder takes design responsibility.

Common Exclusions That Catch Builders Unawares

Even with the right policies, exclusions can destroy coverage. These are the most dangerous for design-and-build contractors.

Exclusion for “Fitness for Purpose” Claims

Many PI policies exclude liability for breach of an implied warranty that the design is fit for a particular purpose. Design-and-build contracts almost always include an express warranty that the design will achieve the client’s stated objectives. If your policy excludes fitness for purpose, and the client claims the design doesn’t work for their intended use, you have no cover.

What to do: Ask your broker to remove this exclusion or add a “fit for purpose” extension. This typically costs 15% to 25% more on the PI premium but is essential for design-and-build work.

Exclusion for Subconsultant Errors

Some PI policies cover only design work performed by your employees, not by external architects or engineers you engage. If you subcontract design, and that consultant makes an error, your policy may decline the claim.

What to do: Ensure your PI policy includes “subconsultant cover” or “vicarious liability for subcontractors.” Also, require your subconsultants to hold their own PI cover with limits at least equal to yours, and name you as an additional insured on their policy.

Exclusion for Design Changes After Contract Signing

Many policies exclude claims arising from design changes made after the contract is signed, unless those changes are approved in writing by your insurer. In a design-and-build project, design evolution is normal—value engineering, council amendments, client variations. If you don’t notify your insurer, you may void coverage.

What to do: Establish a protocol: any design change that affects structural integrity, fire safety, or compliance must be logged and notified to your insurer within 14 days. Some insurers offer a “design variation notification” endorsement for an additional 5% to 10% premium.

How to Structure Insurance for a Design-and-Build Project

The best approach is to integrate insurance requirements into your contract from day one. Here is a practical framework.

Step 1: Define Design Responsibility in the Contract

Your contract must clearly state who holds design responsibility for each element. Use a schedule that lists:

Where you take design responsibility directly, note it explicitly. Where you rely on a subconsultant, note that your liability is limited to their default.

Step 2: Set Minimum Insurance Requirements for Subconsultants

Require every design subconsultant to provide:

Do not accept a certificate that is more than 30 days old. Verify directly with the insurer.

Step 3: Purchase a Combined PI and Public Liability Package

Several Australian insurers now offer combined policies specifically for design-and-build contractors. These bundle PI, public liability, and contract works with a design extension into a single product. Premiums are typically 10% to 15% lower than buying separate policies.

Platforms like BizCover let you compare quotes from multiple insurers in minutes, but for design-and-build work, engage a broker who specialises in construction risk. The complexity of exclusions and endorsements requires professional advice.

Step 4: Maintain a Design Risk Register

Insurers increasingly require evidence of risk management. Maintain a register that logs:

In the event of a claim, a well-maintained register demonstrates due diligence and can reduce the likelihood of coverage denial.

Case Study: The $400,000 Design Error That Wasn’t Covered

In 2024, a Queensland builder with a design-and-build contract for a $1.6 million retirement village unit faced a claim after the architect’s roof design failed to meet cyclone-rated wind load requirements. The roof lifted during a Category 2 storm event, causing $320,000 in damage and $80,000 in ancillary costs.

The builder held public liability and contract works insurance but no professional indemnity. His insurer declined the claim, citing the design defect exclusion. The architect’s PI policy had lapsed. The builder was personally liable for the full $400,000.

He was able to negotiate a settlement of $280,000 with the client by liquidating company assets, but the business closed within six months. The QBCC subsequently issued a compliance notice for failing to hold PI cover, resulting in a $14,500 fine and a 12-month licence suspension.

This case is not unusual. The Australian Small Business and Family Enterprise Ombudsman’s 2025 construction sector report found that 23% of builder insolvencies in design-and-build contracts were directly linked to uninsured design liability claims.

Practical Advice for Builders Entering Design-and-Build Contracts

Do Not Rely on the Architect’s Insurance Alone

Many builders assume that because they’ve engaged a registered architect, the architect’s PI covers all design risk. This is false in two ways. First, your contract with the client makes you primarily liable. The client will sue you, not the architect. Second, the architect’s PI policy may exclude liability for design work performed under a design-and-build contract where the builder directs the design.

Get Annual PI Cover, Not Project-Specific

Project-specific PI policies exist but are more expensive and harder to renew mid-project. Annual PI cover is cheaper overall and provides protection for design work across multiple projects. For a builder doing three to five design-and-build projects per year, annual PI at $12,000 to $18,000 is typical.

Review Your Policy at Every Renewal

Design-and-build insurance is evolving rapidly. In 2025, several major insurers introduced new exclusions for “design coordination errors” and “value engineering failures.” Review your policy wording with your broker at each renewal. Do not assume your cover remains the same as last year.

Budget Insurance into Your Project Price

Include insurance costs in your project pricing. For a $2 million design-and-build project, allocate:

Total insurance cost: $8,500 to $15,000 per project. This is 0.4% to 0.75% of project value. It is a small price for survival.

Conclusion

Design-and-build contracts offer builders greater control and higher margins, but they shift significant professional risk onto your balance sheet. The days of relying on a standard builder’s policy are over. In 2026, with regulators tightening requirements and claims costs rising, you need a dedicated insurance strategy that covers design liability, subconsultant errors, and fitness-for-purpose obligations.

Do not sign a design-and-build contract until you have confirmed your PI policy covers the specific design work you are contracting to perform. Verify your subconsultants’ insurance. And budget for the premiums—they are a cost of doing business, not an optional extra.

The builder who ignores design risk insurance is not being efficient. They are gambling with their company’s future.

Frequently Asked Questions

What is the difference between professional indemnity insurance and public liability insurance for a design-and-build builder?

Professional indemnity insurance covers financial loss caused by design errors, omissions, or negligent advice. It pays for the cost of redesigning a defective element, legal defence, and compensation to the client for economic loss. Public liability insurance covers third-party injury or property damage, but it excludes design-related claims unless you have a professional risk endorsement. For design-and-build work, you need both policies, or a combined product that covers both risks.

Does the QBCC require professional indemnity insurance for builders?

Yes. If you hold a QBCC licence that includes design, such as a design-and-build classification, you must maintain professional indemnity insurance with a minimum of $1 million per claim and $2 million aggregate. This requirement is enforced through licence renewal and random audits. Non-compliance can result in fines up to $23,000 and licence suspension.

Can I rely on my subcontract architect’s professional indemnity insurance to cover design errors?

No. In a design-and-build contract, you are the principal contractor and bear primary liability to the client. The client will sue you, not the architect. While you may have a right of recourse against the architect, that does not protect you from the claim itself. You must hold your own PI cover. Additionally, the architect’s policy may exclude liability when they are working under your direction in a design-and-build arrangement.

How much does professional indemnity insurance cost for a builder doing design-and-build work in 2026?

For a builder with no prior claims, annual PI premiums range from $6,500 to $14,000 for $1 million to $2 million in cover, depending on project values and design complexity. For higher-risk projects such as multi-unit residential or commercial buildings, expect $15,000 to $28,000 per year. Adding a fitness-for-purpose endorsement or subconsultant cover increases the premium by 15% to 25%.

What happens if I don’t have PI insurance and a design error causes a loss?

You will be personally liable for the full cost of the claim, including redesign, rectification, legal fees, and any compensation awarded to the client. In practice, this often forces builders into liquidation or bankruptcy. You may also face regulatory action from your state building authority, including fines, licence suspension, or cancellation.

Does my contract works insurance cover design errors?

Standard contract works insurance excludes damage caused by design defects. However, you can add a design extension endorsement that covers physical damage to the works resulting from a design error. This endorsement does not cover the cost of redesigning the defective element—that falls under your PI policy. The extension typically adds 12% to 18% to the base contract works premium.

How do I check if my subconsultants have adequate insurance?

Request a certificate of currency directly from their insurer, not from the subconsultant. The certificate should show the policy number, coverage limits, effective dates, and your company named as an additional insured. Verify the certificate by calling the insurer’s listed contact number. Do not accept a certificate more than 30 days old. For high-value projects, require a copy of the full policy wording to check for exclusions.

What should I do if I discover a design error mid-construction?

Stop work immediately on the affected element. Notify your professional indemnity insurer in writing within 14 days of discovering the error, even if you are not certain a claim will be made. Document the error, its cause, and any steps taken to mitigate further damage. Engage an independent engineer to assess the issue. Do not attempt to redesign or rectify without insurer approval, as doing so may void coverage.

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