Can Building Contract Terms Be Changed After Signing in Perth?

November 4, 2026    propertysettlementlawyersperthwa
Can Building Contract Terms Be Changed After Signing in Perth?

A signed building contract may seem like the final step of construction projects, but some circumstances can indicate that changing its terms is the most feasible option. During construction, design changes, material substitutions, unexpected site conditions or other adjustments are often the main causes of changes to building contracts. However, changing agreed terms is not simply a matter of reaching a verbal understanding with the builder. Western Australian law sets requirements for certain home building contract variations.

This blog explains when building contract terms can be changed after signing and how variations should be documented. It also explores what homeowners should consider before agreeing to changes and how a building contract lawyer in Perth can help you manage related disputes.

Can a Building Contract Be Changed After Signing in Perth?

Yes, you can change contract terms after the paper is signed, but it can only happen if all parties agree to the proposed variations. Some specific requirements may also apply for changing a building contract after signing in Perth.

A variation in a building contract must:

  • Be recorded in writing.
  • Set out the terms and cost of the variation.
  • State the date of the variation.
  • Be signed by the builder and owner, or their authorised agents.
  • Be provided to the owner before the variation work begins.

What Counts as a Building Contract Variation?

In building contracts, a variation is referred to as changes to the agreed scope, specifications, price and other applicable contractual requirements. These changes are sometimes requested by homeowners or may be needed to complete the project in the right way.

You should document the changes when they alter the contractual obligations or agreed building work. Some of the common examples of changes in building contract variations are:

Changes Requested by the Homeowner

You may decide to change a material, fixture, floor plan element or finish after signing. For instance, you might upgrade kitchen cabinetry or add electrical outlets.

Such changes can affect both the contract price and construction programme. The builder may need to assess whether the requested change is practical within the existing construction stage and complies with applicable building requirements. Before the additional work proceeds, you should ask the builder about any requirements for completing the construction.

Changes Caused by Unforeseen Circumstances

Some circumstances may require changes to a building contract after signing. Under Western Australia’s Home Building Contracts Act 1991, these include:

  • A lawful written direction: A person acting under written law may direct changes to the building work.
  • Unforeseen circumstances: The builder may need to vary the contract because circumstances could not reasonably have been foreseen when the contract was signed.
  • Inclement weather: Severe weather may justify an extension of the completion period under the contract.
  • Specified materials becoming unavailable: If materials specified in the contract cannot be sourced, an acceptable alternative may be required, potentially affecting the completion timeframe.
  • A building permit condition: A condition attached to a building permit may require a change to the contract, which the owner and builder must acknowledge in writing.

Importantly, increased labour or material costs alone may not qualify as unforeseen circumstances.

What Should You Check Before Signing a Variation?

A variation can affect more than the immediate cost of construction. It may also influence the completion date, financing requirements and subsequent building work.

Before signing the building contract variation in Perth, here is what needs to be considered:

  • Scope: Confirm precisely what work is being added, removed or substituted.
  • Cost: Check whether the quoted amount includes GST, labour, materials and associated costs.
  • Programme: Establish whether the variation affects the contractual completion date.
  • Specifications: Ensure revised drawings, schedules or specifications are attached or properly referenced.
  • Payment: Confirm when the additional amount becomes payable under the contract.

What Happens If the Builder and Homeowner Disagree?

If you and your builder are not on the same page about a proposed variation, first establish whether the change is permitted under the contract and applicable law. The next step is to check the original contract, written quotation, variation clause and supporting documents.

You should also ask the builder to explain the change, its costs and what the expected project completion date will be. Keep all of these discussions and responses documented. If you can’t reach an agreement, you may seek assistance from a building contract dispute lawyer in Perth to resolve the situation.

Final Thoughts

Building contract terms can be changed when both parties agree on the proposed changes and the variations comply with applicable laws. Before making any changes, clarify the scope of the modifications, whether additional materials are required, any changes to the contract price and the expected construction completion date. If these changes affect your property transaction or settlement obligations, consulting experienced property settlement lawyers in Perth may help you understand the potential legal implications. Keeping these factors in mind can help you make informed decisions about changes to your building contract.

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