Provisional Sums in Building Quotes: 9 Checks Before You Sign
When comparing quotations for a house renovation, extension or loft conversion, homeowners naturally look at the total price. However, two contractors can submit quotations for the same project with very different levels of cost certainty.
One quotation may include fully specified materials and measured works, while another contains several provisional sums for items that have not yet been designed, selected or investigated.
Both quotations might appear competitive, but the final amounts payable could be considerably different.
A provisional sum is an allowance included for work where the scope, quantity or cost cannot yet be properly established. It is not necessarily the final price of that work.
Understanding provisional sums before signing a building contract is one of the most useful ways to reduce unexpected renovation costs.
These nine checks explain what homeowners should look for, which questions to ask and how to make building quotations easier to compare.
1. Understand what a provisional sum actually means
A provisional sum is an estimated allowance for work that has not been sufficiently defined when the quotation or contract is prepared.
For example, a contractor may allow £3,000 for drainage alterations because the existing underground pipework has not yet been exposed. Once the drainage is investigated and the necessary work established, the actual cost may be higher or lower.
Provisional sums are common in refurbishment projects because existing buildings can conceal conditions that are difficult to establish before opening up.
They are not automatically evidence of poor estimating. However, excessive allowances can indicate that the project is not sufficiently developed for reliable pricing.
2. Distinguish provisional sums from prime cost allowances
These terms are sometimes confused, but they serve different purposes.
A provisional sum generally relates to work whose scope or extent has not been fully established.
A prime cost allowance commonly relates to the supply cost of an item that has not yet been selected, such as sanitaryware or kitchen fittings. The precise treatment depends on the contract.
For example, a bathroom quotation might include an allowance for the purchase of a basin but price its installation separately.
Before accepting either type of allowance, establish what is included.
- Does the allowance cover materials, labour or both?
- Are delivery, waste, overheads and profit included?
- How will the final adjustment be calculated?
3. Identify every allowance in the quotation
A quotation should make provisional sums easy to identify rather than burying them within general descriptions.
Ask the contractor to provide a schedule showing each allowance, its value and the reason the work cannot currently be priced accurately.
Common examples include structural alterations, drainage diversions, electrical upgrades, repairs to concealed timber and specialist finishes.
The total value of these allowances matters. A quotation containing £25,000 of provisional work presents a different level of financial uncertainty from one containing £2,000, even if both have the same headline price.
4. Check whether the allowance is realistic
An allowance should be based on a reasonable assessment of the likely work, rather than simply being set low to make the overall quotation attractive.
Suppose a quotation includes £4,000 for an item that is later properly specified and priced at £9,000.
Depending on the contract's valuation provisions, the difference could increase the amount payable by approximately £5,000, potentially with additional agreed charges or adjustments.
Ask what information supports the original figure and whether comparable work has been considered.
A realistic allowance provides a better basis for budgeting, even if it makes the initial quotation appear more expensive.
5. Reduce uncertainty before construction begins
One of the best ways to reduce provisional sums is to complete more investigation and design work before requesting final quotations.
Structural calculations, drainage surveys, opening-up inspections and detailed specifications can help contractors establish the actual work required.
Not every unknown can be eliminated in an older property, but many can be reduced.
- Complete structural design where practical.
- Investigate drainage and concealed construction.
- Choose principal materials and fittings.
- Resolve important layout and specification decisions.
Spending time on pre-construction preparation can improve pricing accuracy and reduce disruption once the project starts.
6. Understand how provisional sums affect the final account
The treatment of a provisional sum depends on the building contract and the agreed valuation mechanism.
In many arrangements, the original allowance is adjusted when the work is instructed and properly valued. The final cost may reflect measured quantities, agreed rates, quotations or another contractual basis.
It is important not to assume that every provisional sum will automatically be replaced by the contractor's actual expenditure plus a fixed percentage.
Ask how changes will be recorded, approved and valued.
The contractor should provide sufficient information to explain adjustments, including the agreed scope and relevant supporting costs.
7. Compare building quotations on the same basis
The cheapest quotation is not necessarily the lowest-cost proposal once provisional allowances are considered.
For example, one contractor may provide a comprehensive fixed price for electrical work, while another includes a small provisional sum because the electrical specification remains incomplete.
Comparing the totals without adjusting for these differences can be misleading.
Prepare a comparison schedule identifying:
- Fixed-price work included in each quotation.
- Provisional sums and prime cost allowances.
- Excluded work and client-supplied items.
- Differences in specifications and assumptions.
This helps homeowners understand what each contractor has actually priced.
8. Keep a separate renovation contingency
A provisional sum is not the same as a contingency allowance.
A provisional sum relates to identified work that has not been fully defined. A contingency is money reserved by the client for unexpected costs or risks arising during the project.
For example, a quotation may contain a provisional sum for drainage alterations, while the homeowner retains a separate contingency for unforeseen defects elsewhere in the building.
The appropriate contingency depends on the property's age, condition, survey information and complexity of the works.
Avoid treating unused provisional allowances as guaranteed savings or relying on the contingency to compensate for an incomplete specification.
9. Agree the approval process before signing
Before appointing a contractor, establish how provisional work will be authorised and how its cost will be communicated.
Where practical, the contractor should provide an updated price before the work proceeds, allowing the homeowner to understand the financial implications.
Some urgent or concealed work may require a different procedure, so the contract should explain how those circumstances are handled.
Agree who can issue instructions, how approvals are recorded and how adjustments appear in interim valuations and the final account.
A clear process protects both parties and reduces disputes over whether additional work was authorised.
Planning a refurbishment budget with Bayocorp
Provisional sums are sometimes unavoidable, particularly when renovating older London properties. However, they should be clearly identified, reasonably assessed and managed through an agreed contractual process.
Bayocorp delivers whole-house refurbishments, extensions, loft conversions, kitchens, bathrooms and interior fit-outs across London and the South East.
We can help develop a clear scope of works, coordinate pre-construction investigations and prepare a structured quotation that distinguishes defined work from genuine allowances.
Contact Bayocorp before starting your renovation to discuss your project scope, budget and the information needed for a more reliable building quotation.
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