Changing a major domestic building contract - checklist

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Important note: owners have a new duty to notify the Victorian Building Authority (VBA) if the revised final cost of work has increased by $15,625 or more. You must notify the VBA within 28 days of becoming aware. This applies to any building permit issued from 1 July 2019. For more details, view Advising the VBA of the final cost of work on our Managing building project costs page.

Note: The threshold amount:

  • for a major domestic building contract is $10,000
  • above which cost plus contracts are permitted is $1 million.

Your builder must give you a copy of the Domestic Building Consumer Guide before you sign a major domestic building contract. For more information on this and other building law changes, view our Domestic Building Consumer Guide page.

Tips for changing a contract

  • Use a written Variation Notice for all changes to a contract
  • As much as possible, avoid having prime cost and provisional sum items in your contract

You do not have to pay for variations that are ordered to deal with issues that the builder should have identified before starting work.

Legal changes to a building contract

The law only allows certain changes to the price stated in a signed major domestic building contract.

Legal changes to the contract price include:

  • variations to the plans and specifications
  • prime cost items
  • provisional sum items.

Variations to the plans and specifications must be in writing and signed by you and the builder. We recommend you do the same for prime cost and provisional sum items.


Variations are changes to the contract that:

  • you and the builder agree to make
  • a building surveyor (or another authorised person) orders after the contract has been signed and building work has started.

If you do not agree with the changes ordered by an authorised person (building surveyor, architect, building inspector or engineer), you must advise the builder in writing within five business days of receiving the notice.

By law, you and the builder must agree in writing to the variations (using a Variation Notice) and include the details and cost of the changes in the contract (including the new total price and new completion date) before the work commences.

A Variation Notice is not required if you request a variation and your builder reasonably believes the changes will not:

  • require a change to any permits for the project
  • cause delay
  • add more than two per cent to the original contract price.

To avoid disputes, we recommend changes are made in writing and signed by both parties.

Prime cost items

Prime cost items are your selections of fixtures and fittings (for example, ovens, taps and tiles) that are listed items in the contract but which are not specifically identified and costed. This is because you or your builder could not determine or agree the make, model or exact price of the item at the time you signed the contract – you could only estimate the price, which could be less than the final cost.

Where possible, avoid prime cost items. Try to include the specific details of your selections (such as make, model, colour and style) in your contract, so that the building cost is final.

Get a copy of any invoice, receipt or other document that shows the cost of any prime cost item.

Provisional sum items

Provisional sum items are items listed in the contract for possible additional work, such as excavation, where the builder cannot give you an exact price of the work at the time you sign the contract – they can only make a reasonable estimate of the cost.

Where possible, do not agree to provisional sum items as they can make your final cost higher.

For example, it is common for excavation work to be included as a provisional sum item. Be aware that this cost could increase substantially if additional excavation work is needed because rock was not determined in the soil report. Make sure that your builder has obtained a comprehensive soil report in order to give you a reasonable estimate of costs. If you’re unsure, you may wish to seek advice from an independent building consultant.

Your builder must make a ‘reasonable allowance’ for the nature and location of the building site when estimating supply and delivery in the contract price – for example, your builder must allow for transport costs if you are building on a rural property.

Get a copy of any invoice, receipt or other document that shows the cost of any provisional sum item.

Getting out of your contract (cooling off)

You have five business days after receiving a signed copy of your major domestic building contract to withdraw without penalty. This is your ‘cooling-off period’.

If you engaged a lawyer to review your contract prior to signing, then you are not entitled to a cooling-off period.

View our Getting out of a building contract checklist page.