A provisional sum is an allowance included in a builder’s quotation or building contract for work that cannot yet be described or priced with sufficient certainty.

It gives the project a temporary budget figure, but it is not normally a guaranteed final price for that work. Once the scope becomes clear, the provisional allowance should be replaced or adjusted using the valuation method set out in the contract.

For homeowners, the important point is simple: a quotation containing provisional sums includes costs that may move up or down. The more significant those sums are, the less certainty the headline total provides.

Provisional Sum Meaning

Construction guidance distinguishes between firmly priced work and work that remains uncertain.

A provisional sum is used where the builder cannot reasonably provide a fixed price because important information is incomplete. The uncertainty might relate to design, quantity, access, existing conditions, specialist input or the extent of work that will be revealed later.

For example, a quotation might include:

Drainage alterations — provisional sum: £5,000

This means £5,000 has been included within the quotation as an allowance. It does not necessarily mean the drainage work will cost £5,000.

The final amount could be:

Lower, if less work is required
Higher, if the work is more extensive
Replaced by an agreed fixed quotation once the scope is known
Omitted if the work is not instructed or is carried out by someone else, depending on the contract

The contract should explain how the provisional sum is instructed, valued and adjusted.

Why Do Builders Use Provisional Sums?

Provisional sums are used because not every part of a renovation or extension can always be fully designed or investigated before quotations are requested.

Common reasons include:

Structural details have not been completed
Ground conditions are unknown
Drainage routes have not been confirmed
Parts of the existing building are concealed
Specialist contractors have not yet provided prices
Planning or building-control requirements may affect the work
The homeowner has not made a necessary decision
Access is required before the extent of repair can be established
Surveys or opening-up investigations remain outstanding

Using a realistic provisional sum can be more transparent than pretending the cost is fixed or excluding the work without drawing attention to it.

The problem is not the existence of a provisional sum. The problem is an allowance that is unexplained, unrealistic or treated as though it provides the same certainty as a fixed price.

Common Examples in Renovation and Extension Quotes

Provisional sums may be used for:

Foundation work where ground conditions are uncertain
Drainage alterations where routes and depths are unknown
Structural repairs revealed after opening up
Steelwork awaiting final engineering information
Repairs to concealed roof timbers
Damp, rot or infestation treatment
Asbestos removal following testing
Electrical upgrades dependent on inspection
Repairs to existing plumbing or heating systems
Specialist stonework or heritage repairs
Utility-company work or service diversions
Landscaping where the design is incomplete
Making good around uncertain structural alterations

Some of these items may be capable of further investigation before appointment. Others genuinely cannot be resolved until construction begins.

The aim should be to reduce avoidable provisional sums while making unavoidable uncertainty visible.

How a Provisional Sum Is Adjusted

The exact mechanism depends on the quotation and contract, but the basic process is usually:

A provisional allowance is included in the original price.
More information becomes available or the relevant work is opened up.
The builder or contract administrator defines the work required.
A price or valuation is prepared using the agreed contractual basis.
The provisional allowance is removed or credited.
The valued cost of the instructed work is added.
Any permitted overhead, profit, VAT or programme adjustment is applied.

The adjustment should not simply add the complete cost of the work on top of the original quotation while leaving the provisional allowance untouched.

Ask to see the calculation clearly. It should identify the original allowance, the replacement value and the resulting increase or reduction.

Worked Example: When the Final Cost Is Higher

A builder’s quotation includes a £5,000 provisional sum for drainage alterations.

After excavation, the drainage route proves more complicated than expected. The agreed valuation of the required work is £9,000.

Adjustment	Amount
Original provisional sum removed	−£5,000
Agreed value of drainage work added	£9,000
Increase before any other permitted adjustments	£4,000

The project price increases by £4,000 before considering any separately applicable VAT, overhead, profit or time-related cost under the agreed terms.

The £9,000 should not normally be treated as an extra in full without accounting for the £5,000 already included.

Worked Example: When the Final Cost Is Lower

Suppose the same £5,000 drainage allowance is ultimately replaced by agreed work valued at £3,500.

Adjustment	Amount
Original provisional sum removed	−£5,000
Agreed value of drainage work added	£3,500
Reduction before any other permitted adjustments	£1,500

Subject to the contract, the project price should reduce by £1,500.

A provisional sum should not operate only in the builder’s favour. If the actual valuation is lower, the corresponding credit should be shown.

Defined and Undefined Provisional Sums

On professionally prepared projects, you may see provisional sums described as defined or undefined.

RICS measurement guidance uses these terms to distinguish the amount of information available about the work.

Defined provisional sum

A defined provisional sum relates to work that is not completely designed but is described in enough detail for the contractor to understand matters such as:

The nature and construction of the work
Where it will be carried out
How it connects to other work
Its approximate quantity or extent
Relevant limitations

Because the work is sufficiently described, the contractor may be expected to make appropriate allowance for its effect on planning, programming and project preliminaries, depending on the contract.

Undefined provisional sum

An undefined provisional sum is used where the work is not completely designed and there is not enough information to describe its nature, extent or constraints adequately.

For example, repair work beneath an existing structure may remain undefined until demolition or excavation exposes the condition.

Undefined work usually carries greater cost and programme uncertainty. The eventual work may affect duration, access, supervision and other site costs as well as the direct construction price.

These technical labels do not have identical consequences under every contract. If they appear in your documents, check how the proposed contract defines and deals with them rather than relying on the label alone.

Provisional Sum Versus a Fixed Price

A fixed price is intended to price defined work, subject to the terms of the quotation or contract and any agreed variations.

A provisional sum is an adjustable allowance for work that has not been sufficiently resolved.

Fixed price	Provisional sum
Scope should be sufficiently defined	Scope remains partly uncertain
Price is intended to remain fixed for that scope	Allowance is intended to be adjusted
Builder prices the identified work and associated risk	Final value depends on later information or instruction
Changes normally require a variation or contractual adjustment	Replacement of the allowance is expected

Calling an amount a provisional sum does not explain the whole commercial position. You still need to know what uncertainty it covers and how the adjustment will be calculated.

Provisional Sum Versus a PC Sum

The terms are often confused, but they usually address different uncertainties.

A PC sum is generally an allowance for a product or item that has not yet been selected. Examples include tiles, sanitaryware or door furniture.

A provisional sum is generally an allowance for work whose scope or extent cannot yet be properly defined. Examples include drainage alterations or concealed structural repairs.

PC sum	Provisional sum
Usually relates to a product or material selection	Usually relates to an uncertain package of work
Quantity may be known while the selected item is not	Nature, extent or method may remain uncertain
Adjustment often follows the actual product cost	Adjustment usually requires the work to be defined and valued
Installation may or may not be included	Labour, materials, access and programme may all be affected

Always read the builder’s definition. Domestic quotations do not use these terms consistently, and a builder may label a product allowance as provisional even though it operates more like a PC sum.

Provisional Sum Versus an Estimate

An estimate is an indication of what a project or work item may cost. It may change as information develops.

A provisional sum is a particular allowance included within a wider quotation or contract price.

The two can therefore exist together: a builder might provide an overall estimate containing several provisional sums. That offers less cost certainty than a detailed quotation with a largely fixed scope and a small number of clearly explained allowances.

Check the status of the complete document as well as the label attached to individual items.

Provisional Sum Versus Contingency

A provisional sum is allocated to an identified area of uncertain work.

A contingency is a wider reserve held for risks or unforeseen costs that have not been assigned to one specific item.

For example:

Drainage alterations — provisional sum £5,000 identifies a particular uncertain work package.
Project contingency — £10,000 creates a broader reserve for remaining risk.

Neither should be treated as spare money. A contingency also should not conceal work that is already known to be missing from the quotation.

What Should a Provisional Sum Entry Include?

The quotation should provide enough information for you to understand why the allowance exists and how much uncertainty remains.

For every provisional sum, look for:

A clear description of the work
The amount included
The information or assumption supporting it
Whether it is defined or undefined, where relevant
Whether labour, materials, plant and subcontractors are included
Whether access, protection and waste removal are included
Whether design or professional fees are included
Whether VAT is included
Whether overhead and profit will be added
How the work will be instructed
How the final amount will be valued
Whether programme effects are included
What evidence or breakdown will be provided

An entry such as Provisional sum — £10,000 with no description is not useful enough for a homeowner to assess the risk.

How Provisional Sums Affect Quote Comparisons

Provisional sums can make one builder’s quotation appear cheaper even when the likely final project cost is not lower.

Consider two quotations:

Cost position	Builder A	Builder B
Submitted quotation	£96,000	£103,000
Provisional sum for groundworks	£5,000	£12,000
Other scope and specification	Comparable	Comparable

Builder A appears £7,000 cheaper, but the difference is entirely explained by the lower groundworks allowance.

If £12,000 is the more realistic working figure, the quotations may represent broadly the same expected cost. Builder A has not necessarily offered the work for less; it has included less money for an item that will later be adjusted.

When comparing builders’ quotes:

List every provisional sum separately.
Compare the description and assumed scope.
Identify differences in what the allowance covers.
Replace obviously unrealistic figures with a consistent working allowance.
Check whether overhead, profit and VAT are treated the same way.
Compare the adjusted project positions rather than the submitted totals alone.

Do not automatically reject the quote with the lowest allowance. Ask why the figure differs and what information each builder used.

How Much Provisional-Sum Risk Is Acceptable?

There is no universal acceptable percentage.

A small provisional sum for a genuinely uncertain repair may be reasonable. Several large provisional sums covering foundations, structure, drainage and mechanical work could mean that a substantial part of the price remains unresolved.

Assess:

The total value of all provisional sums
Their percentage of the quotation
Whether they concern essential work
How widely the final cost could vary
Whether the uncertainty can be investigated now
Whether the programme could also be affected
Whether your budget can absorb a realistic increase

The question is not simply, “How many provisional sums are there?” It is, “How much cost and programme uncertainty do they leave with me?”

Can a Provisional Sum Be Resolved Before Appointment?

Often, yes.

Possible steps include:

Completing outstanding design work
Obtaining structural engineering information
Carrying out drainage surveys
Commissioning asbestos or specialist surveys
Opening up selected areas with appropriate approval
Confirming product and finish decisions
Obtaining specialist subcontractor quotations
Clarifying building-control requirements
Asking builders to price the same defined assumptions

Further investigation has a cost, and some uncertainty will remain in existing buildings. However, resolving a material risk before appointment may provide better value than carrying a large unknown into construction.

Where the sum cannot be removed, improve its description and agree the valuation procedure.

Questions to Ask About a Provisional Sum

Ask the builder or relevant professional to answer in writing:

What exact work does this provisional sum cover?
Why can the work not be firmly priced now?
What drawings, quantities and assumptions support the amount?
Is the provisional sum defined or undefined under the proposed contract?
Does it include labour, materials, plant and subcontractor costs?
Are access, protection, waste removal and making good included?
Does it include design, testing or professional fees?
Is VAT included?
Will overhead and profit be added to the replacement cost?
How will the work be authorised?
How will the final value be calculated?
Will quotations, invoices or another breakdown be provided?
Will any unused amount be credited in full?
Could the work affect the completion date?
Can further information or investigation reduce the uncertainty before appointment?

Where the answers change the commercial position, ask for the quotation and proposed contract documents to be updated.

Warning Signs

Clarify the position before accepting the quotation if:

The provisional sum has no work description
The allowance appears much lower than competing quotations
Necessary labour or installation is excluded from the allowance
VAT, overhead and profit are not addressed
Several essential work packages remain provisional
The allowance is presented as though it is a fixed cap
The quotation explains how increases are charged but not how savings are credited
The builder intends to add the full actual cost without deducting the original allowance
There is no written approval or valuation process
Programme consequences are ignored
The builder cannot explain the assumptions behind the figure
A provisional sum is being used for work that could reasonably be defined and priced now

No single point proves that the quotation is unsuitable. It indicates where cost or responsibility needs to be clarified.

Frequently Asked Questions

Is a provisional sum included in the total quote?

Usually, yes. The allowance is normally included mathematically within the submitted total. The final contract price may then be adjusted when that allowance is removed and the actual instructed work is valued. Check the wording of the quotation and contract.

Does a provisional sum include labour and materials?

It depends on the description and contract. A provisional sum for a work package may ultimately involve labour, materials, plant and subcontractors, but related preliminaries, overhead, profit, design or VAT may be treated separately. Ask for the basis to be stated explicitly.

Can a provisional sum increase?

Yes. If the required work costs more than the allowance, the contract price may increase. It may also decrease if the work costs less, subject to the contract’s valuation rules.

Is a provisional sum a fixed price?

No. It is generally an adjustable allowance rather than a guaranteed fixed price for the identified work.

Is a provisional sum the same as an estimate?

No. An estimate describes the likely cost status of a project or item. A provisional sum is an allowance included within a wider price for identified work that remains uncertain.

Is a provisional sum the same as a PC sum?

No. A PC sum generally relates to a product not yet selected, while a provisional sum generally relates to work not yet sufficiently defined. Domestic quotations sometimes use the labels inconsistently, so check the actual description.

Who approves spending a provisional sum?

The contract should identify who can instruct the work and how it is approved. Depending on the project, this may involve the homeowner, architect, contract administrator or another authorised person. Do not assume the builder can spend the allowance without following the agreed process.

What happens if the provisional work is not required?

The unused allowance would normally be omitted or credited in accordance with the contract. Confirm the mechanism rather than assuming the original sum becomes part of the builder’s fixed entitlement.

Should I avoid every quote containing provisional sums?

No. Provisional sums can be a legitimate way to disclose genuine uncertainty. Focus on whether each sum is necessary, realistic, clearly described and governed by a fair adjustment process.

Before You Accept a Quote Containing Provisional Sums

Confirm that you understand:

Why each allowance is needed
What work it covers
Which assumptions support it
Whether the figure is realistic
What is included and excluded
How overhead, profit and VAT will be treated
Who will instruct the work
How the replacement cost will be evidenced
Whether savings will be credited
Whether the programme could change
Which risks can be resolved before appointment

A provisional sum is not automatically a red flag. It is a sign that part of the project price remains uncertain and requires active management.

The headline quotation should therefore be read as a combination of fixed prices and adjustable allowances—not as one equally certain figure.

Need Help Checking Provisional Sums?

Before You Build provides independent builder quotation reviews for homeowners before a contractor is appointed.

We assess provisional sums, PC sums, exclusions, vague specifications, missing scope, inconsistencies and potential cost exposure. The purpose is to help you understand which parts of the quotation are dependable, which may change and what should be clarified before you commit.

First Check — £59: an initial review of one builder’s quotation
Full Check — £119: a more detailed assessment of one quotation
Full Comparison — £349: a structured comparison of up to three builders’ quotations

Before You Build complements the work of architects, quantity surveyors, project managers, engineers, surveyors and other professionals. It does not administer the building contract, value completed work, select or recommend a contractor, provide legal advice or replace project-specific professional services.

This guide provides general information for UK homeowners. It is not legal advice, contract administration or a guarantee of final cost. The operation of a provisional sum depends on the wording of the quotation, building contract and project documents. Obtain appropriate professional, consumer or legal advice before making significant financial or contractual decisions.

What Is A Provisional Sum in a Builder’s Quote?