Provisional sums explained

If you have ever looked at a builder's quotation and seen lines marked “PS”, “provisional” or “PC sum”, you are not alone in wondering what they mean. They are a normal part of pricing building work — but they are also one of the most common reasons final costs end up higher than the figure a homeowner first saw.

What is a provisional sum?

A provisional sum is an amount included in a quotation for work that cannot be priced accurately yet, usually because the information needed does not exist. Typical examples include:

• Foundations where ground conditions have not been investigated
• Drainage alterations before the existing runs have been surveyed
• Structural work awaiting an engineer's design
• Repairs to hidden elements, such as timbers or wiring, that cannot be assessed until opened up

The figure is the builder's best estimate. When the work is done, the provisional sum is removed and replaced with the actual cost, calculated on whatever basis has been agreed.

What is a prime cost (PC) sum or allowance?

A prime cost sum — often just called an allowance — is slightly different. It usually covers the supply of items you have not chosen yet: a kitchen, bathroom suites, tiles, flooring or light fittings. The builder allows a figure, say for sanitaryware, and when you make your choice the price is adjusted up or down.

The practical difference is that PC sums are largely within your control, because they depend on what you choose. Provisional sums often depend on what is discovered.

Why they matter

Both are legitimate and often unavoidable. The risk is that they make a quotation look more certain than it is. Two quotes with the same total can carry very different amounts of uncertainty depending on how much sits in allowances.

Things to watch for:

• Allowances that are unrealistically low for what you actually want — a modest kitchen allowance when you are planning something more ambitious
• No explanation of how the sum will be adjusted, or whether overheads and profit will be added
• Provisional sums used for work that could reasonably have been priced with a little more information
• Different builders allowing different amounts for the same item, which distorts a comparison

How to manage them

Reduce them before you sign

Where possible, get the information that turns a provisional sum into a firm price: a drainage survey, trial holes, an engineer's design, or a final kitchen choice. It costs time and some money up front, but it usually leads to a more reliable price.

Check the figures are realistic

Look at each allowance and ask whether it matches what you intend to buy. If you already have a quote from a kitchen supplier, compare it with the builder's allowance.

Agree the adjustment basis

Ask the builder to confirm in writing how each sum will be adjusted — at cost, at cost plus a stated percentage, or at agreed rates — and that you will see supporting invoices or a breakdown.

Normalise when comparing quotes

When you compare quotations, put the same allowance figure for each item across all of them, so you are comparing the builders' prices rather than their guesses. Our guide on comparing builder quotes goes through this step by step.

Keep a running tally

As work progresses and actual costs replace allowances, keep a simple record of the difference. That, alongside any agreed variations, gives you a realistic view of where the final account is heading — and is one reason we recommend a sensible contingency.

Where we can help

Allowances and provisional sums are one of the first things we look at in a Builder Quote Check. We set out how much of each quotation is firm and how much is provisional, flag allowances that look light for the project described, and suggest the questions to ask before you appoint anyone.