Quick answer
What homeowners need to know
A provisional sum is an allowance for work that cannot yet be priced precisely; compare its scope, basis, margin treatment and likely range.
Ask what information would convert each allowance into a fixed figure and when that information will be available.
Key takeaways
- Know the difference between a provisional sum and a prime cost sum.
- Check whether each allowance is realistic for what you want.
- Agree how adjustments will be calculated once the real cost is known.
- Useful budgets separate known scope, selections, allowances, exclusions, GST and contingency.
Costs & budgeting
Reading renovation provisional sums in a quote
Know the difference between a provisional sum and a prime cost sum. A provisional sum covers work that cannot be fully defined yet, such as repairs to hidden framing. A prime cost sum usually covers an item you have not chosen yet, such as tapware or a cooktop. Both are allowances rather than fixed prices, and each is adjusted to the actual cost later.
Check whether each allowance is realistic for what you want. If you are planning premium tapware but the allowance suits a basic range, the difference will come back as an extra cost. Ask the contractor what product or scope each figure is based on, and compare it with your own research. Raising a low allowance now gives a truer picture of the total price.
Agree how adjustments will be calculated once the real cost is known. Find out whether margin applies to the difference, whether labour is included or charged separately, and what records you will see, such as supplier invoices or time sheets. Put this in writing before signing. Clear rules make the final account easier to check and reduce disagreement at the end of the job.
Scope before solutions
Decisions to make before committing
Settle these points before an idea becomes an order, contract or construction instruction.
Ask what information would convert each allowance into a fixed figure and when that information will be available.
extent of demolition and hidden repair
changes to structure, plumbing or electrical services
material grade, access and programme constraints
Practical sequence
A step-by-step planning process
- 01
Define the exact outcome you need and how success will be checked.
- 02
Define the measurable scope and finish level before requesting prices.
- 03
Ask each contractor to identify assumptions, exclusions and provisional sums.
- 04
Keep design, consent, temporary works and owner-supplied items visible in the total budget.
- 05
Retain a project-specific contingency and update the forecast when decisions change.
Cost and time
How to build a more reliable budget and programme
A fixed price or completion date needs a measured scope and a site visit. A site inspection and written scope are required before any planning range can become a reliable project quotation.
Use the calculator, then request a site-specific assessment.
Risk control
Common mistakes to avoid
- A quote with a low allowance can look competitive while leaving the final cost exposed.
- comparing totals without aligning inclusions
- using a generic square-metre rate as a final quote
Accuracy and compliance
Use current official information
Primary sources used for this guide
- Why contracts are valuableBuilding Performance (MBIE)
- Home renovation and repairConsumer Protection New Zealand
- Planning a successful buildBuilding Performance (MBIE)
Common questions
Frequently asked questions
What is a provisional sum in a building quote?
A provisional sum is a placeholder amount for work whose extent is not yet known when the quote is written. Common examples include repairs to concealed damage or work that depends on further design. The figure is adjusted up or down once the work is defined and completed, so the quote total is not fixed for those items.
What is the difference between a PC sum and a provisional sum?
A prime cost, or PC, sum is an allowance for a specific item still to be selected, such as an appliance or tapware. A provisional sum is an allowance for work whose scope is not yet known, such as repairs to hidden framing. Both are adjusted to the actual cost, so check how labour and margin apply to each.
Why is a quote with many provisional sums riskier?
Each provisional sum is an estimate rather than a fixed price, so the more of them a quote contains, the less certain the final total becomes. A quote may look cheaper simply because its allowances are low. Further investigation or design before signing can turn some allowances into firm prices and give you a clearer view of the likely cost.