If you are comparing building quotes and one of them looks cheaper, provisional sums are one of the first things worth checking. They are not automatically a problem. In some cases they are the most honest way to show that part of the job is still unclear. But they do matter because they lower price certainty. A quote with several large provisional sums can look tidy at the top line and still move quite a bit once the real scope becomes clear.
For homeowners, the simplest way to think about a provisional sum is this: it is not a fixed commitment for a fully defined piece of work. It is an allowance for work or cost that cannot yet be pinned down properly when the quote goes out.
Need a clearer project budget before you choose between quotes?
If allowances, scope gaps or half-defined items are making the numbers hard to compare, a proper estimate route can give you a firmer baseline before you commit.
Quick Quote is the fast order-and-pay route to book in professional estimating work when the scope is already clear.
- Useful for homeowners comparing builders on a like-for-like basis
- Helpful when one quote looks cheaper mainly because more of the uncertainty sits in allowances
- Useful when drawings exist but the price still feels hard to trust
Direct answer: what is a provisional sum in a building quote?
A provisional sum is an estimated allowance for work that has not been fully designed, measured or specified at the point the builder prepares the quote. It is included so the builder can produce a price even though part of the scope is still uncertain.
That uncertainty might be about quantity, method, access, product choice or site conditions. Common examples include drainage alterations, groundworks, steelwork details, kitchen or bathroom supply allowances, landscaping, electrical upgrades or specialist joinery that has not been fully selected yet.
The part many homeowners miss
The important point is not just what the provisional sum covers. It is what it says about the certainty of the quote. A quote with one or two small provisional sums may still be fairly robust. A quote with several large ones is telling you that the final cost is still carrying a fair amount of movement.
That is why the cheapest quote is not always the cheapest route through the project. Sometimes it simply means more of the unknowns have been pushed into allowances that will be adjusted later.
Provisional sums are not always bad
This is where a lot of generic advice goes wrong. It is too simplistic to say provisional sums are a red flag and should never appear. On real projects, some uncertainty is normal. If drainage runs are not confirmed, steel is not finalised, or bathroom fittings are still undecided, showing an allowance can be more honest than pretending the item is fixed.
So the better question is not, “Does the quote contain provisional sums?” It is, “Are they reasonable, clearly described, and limited to parts of the job that are genuinely not settled yet?”
Treat each provisional sum as a risk label, not a fixed price
A good way to read a quote is to treat every provisional sum as a marker saying: this part of the budget could still move. That does not mean it will definitely rise, but it does mean the headline figure is carrying less certainty than a fully specified item.
If one builder includes a £3,000 provisional sum for drainage and another includes £8,500, do not assume the first builder is better value. One may be underallowing. The other may be pricing more cautiously because they have thought harder about risk, access, depth, connections or reinstatement.
For example, a quote at £92,000 with £14,000 sitting in provisional sums may be less settled than a quote at £98,000 with only £4,000 in allowances. The first number can look cheaper at headline level while still carrying more room to move once drainage, steel, finishes or service details are properly pinned down.
Where provisional sums usually show up in UK residential work
- Groundworks where excavation depth or soil conditions are still uncertain
- Drainage alterations before runs and connections are properly confirmed
- Structural steel where engineering is not final yet
- Kitchens, bathrooms or tiles where the finish level is not fully chosen
- Electrical upgrades where the extent of remedial work is not yet clear
- External works, landscaping or retaining details not locked down at quote stage
How provisional sums affect quote comparison
If you are comparing builders, provisional sums matter because they can distort the apparent gap between quotes. One quote may look lower simply because more items are sitting in rough allowances. Another may look higher because the builder has included firmer numbers or has allowed more realistically for awkward parts of the job.
That is why a like-for-like quote comparison should not stop at the total. If you do not fully understand the allowances, you are not really comparing fixed prices. You need to compare:
- how many provisional sums appear
- how large they are
- how clearly each one is described
- whether the same items are provisional across every quote
- whether one builder has quietly omitted risk that others have priced for
A simple three-check test before you accept a quote
1. Count them
A couple of modest provisional sums on a half-settled project is one thing. A quote heavily built around them is another.
2. Look at size, not just number
One large provisional sum can matter more than four tiny ones. Focus on the items that could move the budget materially.
3. Check the explanation
A good quote should tell you what the allowance relates to and why it is provisional. If it is vague, it is harder to judge whether the figure is sensible.
Provisional sums vs prime cost items: not the same thing
These terms often get blurred together, but they are not identical. In simple terms, a prime cost item is usually an allowance for the supply of a product you have not selected yet, such as sanitaryware or tiles. A provisional sum is broader and can cover both materials and labour for work that is not properly defined.
You do not need to become a contract specialist to compare quotes properly, but it does help to know that both of these allowances can move. If a quote contains several PC items and several provisional sums, the final number is less settled than the headline price suggests.
Questions worth asking the builder
- What exactly does this provisional sum include?
- Why is it still provisional at this stage?
- What information would be needed to firm it up?
- Is this figure based on a low, mid or high specification assumption?
- What tends to make this item go up once work starts?
Those questions are often more useful than simply asking, “Can you reduce the price?” A cleaner scope usually beats a forced lower number.
How to reduce the number of provisional sums in a quote
You usually reduce provisional sums by improving information before pricing, not by arguing about the allowance after the fact.
- Provide better drawings and details
- Make key finish selections earlier
- Clarify what is included and excluded
- Resolve structural and services information where possible
- Ask for the quote to be updated once missing details are known
The more settled the scope is, the more fixed the quote can become.
When a baseline estimate helps
If the quotes in front of you are hard to compare because allowances are doing too much of the work, it can help to get an independent estimating baseline. That gives you a clearer sense of whether the moving parts sit in a sensible range before you choose a builder.
This is especially useful on extensions, refurbishments and mixed-scope projects where drawings exist but a lot of specification and risk detail is still moving underneath the surface.
Bottom line
Provisional sums are not automatically bad, but they are never just background admin. They are one of the clearest signals that part of the quote is still carrying uncertainty. Read them that way, compare them carefully, and be cautious of any quote that looks cheaper mainly because more of the real cost has been left to move later.
Want a clearer baseline before you choose a builder?
Use the route that matches how settled the project is.
- Request a Quote if the project is broader, more detailed or still evolving
- Order a Quick Quote if the scope is already clear and you want to book in professional estimating work faster
