What Provisional Sums Really Mean

What is a provisional sum?

A provisional sum is an estimated allowance in a building contract for work or materials that cannot be accurately priced at the time the contract is prepared.

In simple terms, it is a placeholder figure. It gives the contract a number to work with, but that number may go up or down once the actual cost becomes known.

Provisional sums are usually used when something has not been fully selected, measured, designed or investigated yet. That is why they deserve close attention. They are not automatically a problem, but they do create uncertainty.

Why builders use provisional sums

There are legitimate reasons builders include provisional sums. Sometimes the final detail is genuinely unknown at the quoting stage. For example, a builder may not know exactly how much excavation will be required until work starts, or which fixtures the owner will choose later.

Common examples of provisional sums include:

• earthworks and site preparation
• drainage or stormwater works
• driveways and external paving
• retaining walls
• kitchen, bathroom or laundry selections

Used properly, provisional sums can help keep the contract moving while some details are still being finalised. The issue is that they can also make a contract price appear more certain than it really is.

Why provisional sums matter so much

The main risk with provisional sums is simple: if the allowance is too low, you pay the difference later.

That means a contract that looks affordable on day one can become much more expensive once real costs come through. This is one of the most common causes of unexpected budget increases during a build.

For example, a provisional sum for site works may look reasonable in the paperwork. But if the block has difficult soil, rock, fill, slope or drainage issues, the final cost may be significantly higher. The same applies to fixtures and finishes if the allowance only covers very basic selections.

This is why we encourage homeowners to look beyond the headline contract price. A lower quote is not always the safer quote if it contains unrealistic provisional sums.

How to tell if a provisional sum may be too low

Not every homeowner knows what a realistic allowance should be, and that is exactly why provisional sums can be so easy to miss. There are a few warning signs worth watching for.

Be cautious if:

• there are many provisional sums throughout the contract
• the allowances seem vague or poorly explained
• the figures look low compared with your expectations
• major parts of the build are still not clearly specified
• the builder cannot explain how the allowance was calculated

If a provisional sum covers something important, ask what assumptions were made. Was the amount based on actual site information, standard entry-level products, or a rough estimate just to complete the paperwork?

The more detail you have, the easier it is to assess the real risk.

What you should do before signing

The best way to manage provisional sums is to reduce uncertainty before the contract is signed wherever possible.

That might mean:

• finalising more selections earlier
• getting clearer specifications in writing
• asking for supporting detail behind each allowance
• checking whether site investigations have been done properly
• understanding which provisional sums are most likely to change

If an allowance cannot be avoided, make sure you understand what it includes and what could cause it to increase. This puts you in a much stronger position than simply accepting the figure at face value.

If you want a second set of eyes before committing, our pre-contract review service can help identify contract risks and unclear allowances. We also support clients through inspections and build-stage concerns with our independent building inspections.

Provisional sums are not just paperwork

It is easy to treat contract allowances as small print, but provisional sums can have a real impact on your final build cost. They deserve the same attention as your floorplan, inclusions and timeframe.

Zac regularly sees contracts where provisional sums were technically disclosed, but not properly understood by the owner. A short conversation before signing can often make the difference between feeling informed and being caught off guard later.