The drainage route cannot be confirmed until the ground is opened, but the customer wants one price before work starts. A builder provisional sums quote can carry that uncertainty without pretending the work is already fixed.
Give the unknown work its own reference. State what the sum covers, what will make the work priceable and how you will replace the sum once the facts are known. Do not use it as spare money for the job.
Decide what a provisional sum means before using one
A provisional sum is an amount included for work that the accepted contract or quotation terms allow to be valued later. The label alone does not permit an adjustment. The accepted terms must say how the work is instructed, valued and used to replace the original sum.
Some UK contracts distinguish between defined and undefined provisional sums. A defined sum carries enough information about the nature, quantity, location and programme of the work for the builder to account for its effect. An undefined sum does not provide that information. Use the distinction and valuation method written in the accepted contract rather than inventing your own meaning on the quote.
A builder provisional sums quote should tie each sum to a named uncertainty. A drainage sum might cover a route that cannot be confirmed before excavation. A roof repair sum might cover concealed timber that can only be inspected after the covering is removed. Each sum needs a location, a reason and a boundary.
The customer-facing sum is also not automatically the same as your internal cost allowance. Your internal figure may record expected labour, materials and subcontractor costs. The quote figure must follow the selling-price basis stated in the customer document, including its treatment of overhead and markup.
Show that the quote total can change
Put the provisional sum in the displayed quote total if that is how your quotation is structured. Label it as adjustable beside the total. The customer should not have to find that fact in a note at the end.
State whether the sum will be removed or credited before the replacement price is added. Also state whether a lower replacement price produces a credit and a higher one produces an additional charge under the accepted document.
Do not call the sum a maximum, minimum or guaranteed price unless your actual agreement makes it one. A provisional figure is there because part of the work remains unresolved.
Choose the pricing treatment before costing the work
Keep fixed scope, provisional work, a product allowance and an exclusion separate. Pick the treatment before adding costs.
Fix the price when the work is known
Use a fixed price when you know the quantity, condition, access and installation method. Price the labour, materials, plant, subcontractor work, overhead and markup needed to finish that scope.
Known work should not sit inside a provisional sum. If the wall preparation, pipe position or fitting method is already clear, price it now. Leaving known work provisional makes the quote harder to compare and easier to dispute.
Use a provisional sum for incomplete work scope
Use a provisional sum when an important part of the work cannot be confirmed through a reasonable pre-quote inspection. Name the hidden condition or missing fact.
Good examples are a concealed drainage route, timber hidden below a roof covering or foundations that need opening up before their condition can be assessed. The sum should relate only to that unresolved part.
Do not write “unknown building work” as a broad line. Split unrelated risks. Each one may become priceable at a different point.
Use the contract term for an unchosen product
An unchosen product deals with a different problem. The work is understood, but the customer has not chosen the finished item.
Use the term in the accepted UK contract, such as product allowance or prime cost item. State what that term covers. For unfinished sanitaryware selection, price the known preparation and installation separately. Carry the product amount against an assumed size, service position, accessories and fitting method. If the eventual choice changes the installation, price that change separately.
Builder quote allowances become unreliable when product choice and concealed work share the same figure. A product choice is resolved by a customer selection. Concealed work is resolved by inspection or opening up.
Exclude work you are not offering
An exclusion carries no money for the excluded work. It says the work sits outside your offer.
Useful quote exclusions name the exact boundary. Examples include making good by others, concealed damage excluded pending opening up, or service relocation not included. Put each exclusion beside the affected scope rather than hiding every exclusion in one block.
If you need to improve the rest of the quotation before adding adjustable items, follow the practical steps for writing a clear quote.
Inspect the site and narrow the uncertainty
Do not set a round sum from the van. Inspect everything that can be inspected without destructive work. The aim is to make the unknown area smaller.
For each proposed sum, record:
- The room, elevation or work area.
- The visible quantity and your quantity assumption.
- Access for labour, plant and deliveries.
- Existing surfaces and services.
- Protection, removal and making good already known.
- The concealed fact that prevents a fixed price.
- The opening-up work or decision needed next.
Photograph the wider area and the detail. Label the files with the provisional-sum reference. A close-up of damaged timber is little use if nobody can tell which roof slope it came from.
Record opening up in the site diary
Suppose the customer instructs you to open a wall. Record who gave the instruction, what was opened, what was found and what work stopped while you priced the result.
Use the site diary for photographs, site conditions and conversations. The diary supports the quote record. It does not replace an authorised instruction or agreement of the resulting price.
Keep the record with the job using the same method as a refurbishment builder site diary. That gives you a dated trail from the first assumption to the exposed condition.
Name the event that will make the work priceable
Every provisional sum needs a trigger. It might be excavation to a stated point, removal of a roof covering, completion of a survey or receipt of a specialist design.
Write what you will inspect when that event occurs. Then state that you will define and price the work before dependent labour, materials or subcontractors are committed.
If newly exposed work raises a building regulations approval question, check the project route with building control (opens in a new tab) or building standards in Scotland (opens in a new tab). Check before work that depends on the answer starts.
Build the sum from stated cost buckets
Separate the known scope first. Then build the provisional basis from the unresolved work only.
Build the known-work selling price from labour, materials, plant and subcontractor costs. Record whether overhead sits inside that cost base or is recovered through markup. Then state exactly which costs receive markup.
Your provisional sum needs a written basis covering the cost buckets you can reasonably identify. State whether it carries labour, materials, plant, subcontractor work, site costs, overhead and markup. Do not leave the reader to guess.
The unresolved quantity may stop you producing a fixed total. It does not stop you stating what types of cost the sum includes.
Keep labour and materials visible
If opening up is already part of the fixed scope, price it there. If only the extent of repair remains unknown, keep the repair provisional.
Do the same with materials. Known protection and disposal should not disappear into the unknown-work pot. Keep the buckets boring. The quote should show which work is fixed and which fact remains unresolved.
Plant and subcontractor costs need the same treatment. State whether the provisional basis includes access equipment, waste handling, specialist attendance or design work. If one of those items is excluded, name it.
Follow the accepted valuation and markup method
Read the accepted contract before setting the calculation. Its valuation method takes priority. Record which direct costs receive markup, whether overhead is already inside the cost base and how the replacement work will be valued.
Do not recover overhead inside the cost base and then add it again through markup. Do not change the method because the final repair is larger than expected. Compare the provisional figure and replacement price on the same contractual basis.
Markup is what you add to the stated cost base to reach a selling price. Margin is profit as a share of the selling price. If you need to test your own figures, use the profit margin calculator with costs from the same scope.
Check VAT and CIS for their separate jobs
VAT can affect the amount displayed to the customer and the way an adjustment appears on the quote or invoice. Check the current HMRC VAT guidance (opens in a new tab) before issuing the document.
CIS concerns qualifying payments between contractors and subcontractors. It does not apply to every customer quote. Check the current HMRC CIS guidance (opens in a new tab) when the job includes payments that may fall within the scheme.
Write the builder provisional sums quote as a schedule
Give every sum a reference. Link that reference to the scope, site records, authorised instruction and invoice adjustment that follow.
Use a single schedule. Keep the decisions needed to control the work in the same row.
| Field | Record |
|---|---|
| Quote and sum reference | [Quote number and PS reference] |
| Work and location | [Named unresolved work and exact location] |
| Reason and assumption | [Missing fact and assumed condition or quantity] |
| Included cost basis | [Labour, materials, plant, subcontractors and site costs included] |
| Overhead and markup | [Whether overhead is in the cost base, which costs receive markup and the accepted valuation method] |
| Known work priced separately | [Fixed preparation, opening up or installation] |
| Exclusions | [Work and costs outside the sum] |
| Quote-total treatment | [Included in or outside the displayed total] |
| Trigger and timing | [Inspection, opening up, design or selection needed, and when] |
| Authority and price status | [Who may instruct, what has been instructed and whether the price is agreed] |
| Replacement and invoice record | [Original sum removed or credited, replacement price, variation and invoice reference] |
Plain wording can read: “PS-[reference] covers [work] at [location], based on [assumption]. It includes [cost basis] and excludes [items]. After [trigger], the authorised person named in the contract may instruct the defined work. The original sum will then be removed or credited and the replacement work valued under the accepted terms.”
Turn the provisional item into instructed work
Stop at the trigger. Inspect the exposed condition and describe the final scope in measurable terms.
Record quantities, labour tasks, materials, access, disposal, making good and subcontractor work. Attach photographs or drawings. Then build the replacement price using the valuation basis in the accepted contract.
Keep three decisions separate. Get authority to open up before carrying out destructive inspection. Once the condition is exposed, get the defined work instructed by the customer, contract administrator or other person named in the contract. Record whether the price is agreed before committing dependent labour, materials or subcontractors.
A site instruction is not automatically authority for every resulting cost. Issue the variation or valuation record required by the accepted contract. Show the provisional sum being removed or credited and the replacement price being added.
A note in the site diary is evidence of what happened on site. It is not an instruction from an authorised person, and it is not agreement of the price. If the diary records an instruction to open a wall but no resulting work or price was authorised, stop and put each decision in writing.
Use Oak Street to mark the approval boundary
Oak Street is an electrical house example, not a provisional-sum calculation. R. Chen’s quote Q-1847 covered a bathroom exhaust fan, ducted through the roof, and four LED downlights for 1,105 sample currency units.
The ceiling was lined and chasing was excluded. Extra cable and chasing were approved on site as a 160 variation. Invoice INV-1847 was therefore 1,265.
The lesson is the boundary. Excluded work became defined, priced and approved before it reached the invoice. Do not relabel that 160 variation as a provisional sum.
Reconcile the sum without losing the original credit
Use the same cost basis on both sides of the comparison. If the provisional sum included labour, materials, plant, overhead and markup, value the replacement work on the basis required by the accepted contract.
Calculate the final adjustment by removing or crediting the original provisional sum, then adding the replacement price under the written method.
Do not add the full replacement price while leaving the original sum untouched in the quote total. That makes the customer pay for both figures.
Keep product selection differences separate from changed installation work. If a customer chooses different sanitaryware, reconcile the matching product allowance or prime cost item. If that choice also requires service relocation or structural work, put that work on a separate variation line.
The invoice or stage valuation should show the provisional-sum reference, the original credit, the replacement work and the resulting adjustment. The customer should be able to follow it without rebuilding your calculation from emails.
Set up the live register before sending the quote
Create a register for every open provisional item. Record the quote reference, sum, trigger, site finding, authorised instruction, price status, variation and invoice adjustment in a single row.
Review the builder provisional sums quote before ordering materials, booking subcontractors or closing a stage invoice. Close each open item only when the instruction, valuation and adjustment records agree.