Extension Contract Review Before You Sign

A home extension contract is where the drawings, quotation and promises made during early discussions become a binding plan for your property, budget and timeline. A careful extension contract review before signing can prevent the most common causes of renovation stress: unclear inclusions, unexpected costs, approval delays and disputes about who was responsible for what.

For Sydney homeowners, this review should go beyond checking the total price. A well-prepared building contract needs to reflect the actual project, account for NSW requirements and give both homeowner and builder a clear process for decisions that will inevitably arise once work begins.

Why an extension contract deserves close attention

An extension is not a standard product with a fixed set of parts. Conditions below the existing house, access to the site, the age of the structure, consultant requirements and selections can all affect the work. The contract should make those variables visible rather than hiding them behind a single headline figure.

A low price can look appealing if the scope is brief, but it may leave substantial items to be treated as extras later. On the other hand, a detailed contract may appear more expensive because it identifies the work required upfront. The right comparison is not simply one total against another. It is whether each builder has allowed for the same drawings, finishes, approvals, site conditions and level of project management.

For larger residential building work in NSW, your contract must also meet the requirements of the Home Building Act 1989. Depending on the nature and value of the work, this may include a written major works contract and Home Building Compensation Fund cover. It is sensible to confirm the applicable requirements for your project before work starts, particularly where an extension is being delivered alongside renovation, structural or heritage work.

Start with the scope, not the contract sum

The scope of work is the foundation of the agreement. It should be supported by approved or sufficiently developed plans, engineering details, specifications and a schedule of finishes. If these documents are incomplete, the contract needs to state what has not yet been selected or documented and how it will be priced.

Read the inclusions line by line. Does the extension include demolition, excavation, temporary protection, structural steel, insulation, windows, roofing, waterproofing, painting and final cleaning? Does it allow for connecting new services to the existing home, making good disturbed areas and disposing of demolition material?

The same care applies to work outside the new footprint. A rear extension may require changes to drainage, electrical switchboards, hot water systems, paving, landscaping, fencing or the existing roof. These are not always included by default. A clear exclusion is not necessarily a problem, but it should be deliberate and understood before you commit.

Check allowances and provisional sums

Two contract terms deserve particular attention: prime cost items and provisional sums. A prime cost item is generally an allowance for something to be selected, such as tapware, tiles or appliances. A provisional sum is an estimated allowance for work where the full cost cannot reasonably be known at contract stage, such as excavation in uncertain ground conditions.

Neither is inherently unacceptable. They are often necessary in an extension project. The concern is the volume and size of allowances. If major components are provisional, the final cost may move considerably from the contract sum. Ask what assumptions have been used, whether labour is included, what margin applies to adjustments and what information could reduce the uncertainty before signing.

Make sure the price explains itself

A transparent contract should identify the contract price, GST treatment, deposit, progress payments and any allowances. Payment stages should align with meaningful construction milestones, not simply dates on the calendar. You should be able to see what has been completed before each payment falls due.

Review whether the quoted price includes council, certifier, engineering or consultant costs. Approval pathways differ across Sydney sites, and some projects require a development application while others may be suitable for complying development. The contract should be clear about who coordinates approvals, which fees are included and whether the price relies on a particular approval outcome.

Also confirm how the builder will handle latent conditions. Hidden issues are common in older homes: unsuitable soil, undocumented services, termite damage, asbestos, deteriorated framing or non-compliant existing work. A responsible contract cannot promise that no hidden condition will ever be found. It can, however, set out the notification, evidence, pricing and approval process if one is discovered.

Review the extension contract timeline realistically

The start date and completion period need context. A builder cannot reasonably control the time taken for council decisions, authority connections, owner selections or extreme weather. Yet the contract should still identify what needs to happen before commencement, how extensions of time are managed and how delays will be communicated.

Check whether the construction period begins only after approvals, finance, site access, final documents and required insurance are in place. This is often more useful than a vague promise to start shortly after signing. It gives everyone a practical understanding of the conditions needed to mobilise the project.

Where a completion date matters, consider the treatment of delay costs. Some contracts include liquidated damages, which are an agreed daily amount payable if the builder is responsible for missing the completion date. Whether this is appropriate depends on the project, access arrangements and how settled the design is. The clause should be fair, clearly drafted and balanced with legitimate extensions of time.

Variations should be documented before the work changes

Most extension projects involve some changes. You may decide to upgrade a benchtop, move a window or add joinery once you see the space taking shape. Equally, a structural or compliance issue may require additional work. The aim is not to pretend variations will never occur. It is to prevent verbal instructions becoming expensive misunderstandings.

Your contract should require variations to be written, priced and approved before the relevant work proceeds wherever practical. The document should explain the effect on both cost and time. If urgency makes prior approval impossible, such as work required to make a site safe, the contract should state how the builder will notify you and provide supporting information.

Be cautious about signing a contract while expecting major design changes later. Changes made after documentation, approvals and ordering can cost more than the item itself because they may affect trades, lead times and completed work. Finalising key layouts, fixtures and finishes before construction is one of the best ways to protect the budget.

Confirm responsibility for approvals, quality and site management

A home extension involves more than building the new rooms. Someone must coordinate certification, inspections, engineers, trades, deliveries, site safety and the protection of occupied parts of the home. The contract should identify the builder’s role and your responsibilities, including access, decision timeframes and the supply of any owner-provided materials.

If you will remain living in the home, discuss how the site will operate. Consider temporary access, dust control, working hours, bathroom or kitchen arrangements, security, rubbish removal and protection of children and pets. Some disruption is unavoidable, but a practical pre-construction plan reduces surprises once trades are on site.

Quality should also be described in objective terms. The agreement should reference the relevant plans and specifications, Australian Standards where applicable and the process for inspections and defects. At practical completion, there should be a clear handover process covering the final inspection, outstanding items, warranties, certificates and operation information for installed products.

Get independent advice when the risk is high

A builder can explain the project documentation and how their delivery process works, but they cannot provide independent legal advice to a homeowner. For a substantial extension, particularly one with complex site conditions, heritage controls, extensive provisional sums or a significant financial commitment, having a construction lawyer review the contract is a sensible safeguard.

You may also benefit from independent advice from your designer, architect, building consultant or quantity surveyor where the drawings and scope are still evolving. The cost of clarification before signing is usually far lower than resolving a disagreement after demolition has started.

At H.E.A.R, we believe a contract should give homeowners confidence rather than create more questions. Take the time to ensure the documents match the home you want to build, the price you understand and the process you expect. A clear agreement does not remove every construction risk, but it gives everyone the right framework to deal with issues professionally when they arise.