If you’ve received a building quote recently, you’ve probably seen the words “provisional sum” somewhere in the fine print. Most homeowners gloss over it — and that’s where budget surprises come from.
This guide explains exactly what a provisional sum is, why builders use them, and what you should ask before you sign anything.
What Is a Provisional Sum?
A provisional sum (often shortened to PS) is an estimated allowance included in your quote for work that can’t be accurately priced at the time of quoting.
Think of it like a placeholder. Your builder knows that work needs to happen — but because the full scope or specification isn’t confirmed yet, they can’t give you a fixed price for it. So they insert a reasonable estimate instead.
Common examples include:
- Earthworks and site preparation (until the ground is actually assessed)
- Electrical and plumbing work (until designs are finalised)
- Kitchen or bathroom fixtures (until you’ve chosen your specific products)
- Unforeseen conditions inside walls or under floors
Why Do Provisional Sums Exist?
Builders include provisional sums for one of two reasons. Either the work genuinely can’t be scoped until construction begins — like what’s inside a wall during a renovation — or the homeowner hasn’t made a selection yet, like choosing tiles or a kitchen benchtop.
In both cases, the provisional sum protects both parties. It keeps the project moving forward without waiting for every single decision to be made upfront, while still giving you a realistic picture of likely costs.
The Important Part — Provisional Sums Can Go Up or Down
This is what catches homeowners off guard. A provisional sum is not a fixed price. When that part of the work is actually carried out, the real cost replaces the estimate — and it may be higher or lower than what was in your quote.
If you chose more expensive tiles than the allowance covered, the cost goes up. If the earthworks turned out to be straightforward, the cost may come in under the estimate.
What’s the Difference Between a Provisional Sum and an Allowance?
These two terms are often used interchangeably, but there is a subtle difference.
A provisional sum typically covers work where the full scope is unknown — the builder will manage and price the work once it can be properly assessed.
An allowance is usually a budget figure set aside for a product or material selection you haven’t made yet — like a $3,000 allowance for bathroom tapware. Once you choose your tapware, the actual cost replaces that figure.
Both carry the same risk: if the real cost exceeds the estimate, you pay the difference.
Questions to Ask Your Builder Before You Sign
Before signing any building contract, go through the quote line by line and ask your builder:
- Which items in this quote are provisional sums or allowances?
- What are these estimates based on — and how confident are you in them?
- What’s the realistic range — could this cost more, and by how much?
- What decisions do I need to make, and by when, to lock in the price?
A good builder will walk you through every provisional sum without hesitation. If they can’t explain why an item is a PS or what it’s based on, that’s worth probing further.
How Ascend Works Handles Provisional Sums
At Ascend Works, we include provisional sums in quotes only where genuinely necessary — and we always explain exactly what each one covers and why it can’t be fixed-priced at this stage.
We also flag decisions you’ll need to make early, so that PS items can be converted to fixed prices as quickly as possible. The goal is no surprises — just clear, honest communication at every stage of your build.
If you’re looking at a quote and want a second opinion on what the provisional sums mean for your budget, get in touch. We’re happy to help you read between the lines.