A construction project rarely finishes exactly as originally planned. Clients request design changes, materials become unavailable, site conditions create unexpected work and project specifications evolve. These changes can create additional revenue opportunities for contractors, but they can also reduce profitability when the work is not properly priced, approved and recorded.
A contractor may complete several additional tasks during a project and assume that the client will pay for them. However, if the scope, price and contractual approval have not been documented properly, recovering the full cost can become difficult.
For construction businesses, variation management is therefore not just a contract administration issue. It is an important part of financial control. Working with experienced construction accountants in the UK can help businesses maintain reliable project records, monitor additional costs and understand how changes affect reported profitability.
What Is a Construction Variation?
A construction variation is a change to the work originally agreed under a construction contract. Depending on the contract, it may involve adding work, removing an item, changing materials, altering specifications or modifying the sequence of activities.
For example, a contractor may originally agree to install standard flooring throughout a commercial property. During the project, the client requests a higher specification finish in several rooms.
The additional work may involve:
More expensive materials.
Additional labour hours.
Specialist subcontractors.
Changes to the installation programme.
Additional delivery or handling costs.
Delays to other activities.
Extra supervision and site management.
The contractor needs to understand the full financial impact before treating the change as additional profit.
The terminology and procedure depend on the contract being used. JCT contracts commonly refer to variations, while NEC contracts use their own change-control terminology, including compensation events. Contractors should follow the specific notification, quotation, valuation and approval requirements in their agreement.
1. Why Unrecorded Additional Work Creates Financial Risk
One of the most common mistakes in construction is allowing additional work to begin without establishing how it will be valued and paid for.
A site manager may receive a verbal instruction from the client. The contractor completes the work to avoid delaying the project, but the commercial team does not receive the instruction or supporting evidence.
When the contractor later submits an invoice, the client may dispute the additional amount or argue that the work was already included in the original contract.
The business can then face several problems:
Additional labour costs without corresponding income.
Materials purchased for disputed work.
Delayed certification and payment.
Disagreements over the agreed price.
Reduced project gross profit.
Pressure on working capital.
The solution is to create a formal process for recording every significant change, even when the work appears relatively small.
2. Introduce a Variation Register for Every Project
A variation register provides a central record of changes throughout the project.
Instead of relying on emails, handwritten notes and separate spreadsheets, the contractor should maintain one schedule showing the current position of every variation.
A useful register should include:
Project name and reference.
Original contract description.
Variation reference number.
Date the change was requested.
Person or organisation requesting the change.
Description of additional or omitted work.
Estimated cost.
Quoted selling price.
Approval or instruction status.
Expected completion date.
Actual cost incurred.
Amount included in the payment application.
Amount certified and paid.
Outstanding balance.
It is also useful to distinguish between proposed, quoted, instructed, completed, certified and paid variations.
These stages are not interchangeable. A quotation sent to a client does not necessarily mean that the additional work has been approved, and completed work is not automatically the same as work that has been certified for payment.
3. Calculate the Full Cost Before Submitting a Variation Price
Contractors sometimes calculate a variation by looking only at the cost of materials and labour.
This can produce an unrealistic price because additional work may create indirect costs that are not immediately obvious.
A proper cost assessment should consider:
Labour
Calculate the expected hours for each trade, including supervision and any additional working time required.
Materials
Include purchase prices, delivery charges, wastage, handling and any additional material requirements.
Plant and equipment
Consider machinery hire, equipment use, fuel, transport and additional operating time.
Subcontractors
Obtain written quotations and confirm what is included in their prices.
Preliminaries
Additional work may increase site supervision, security, welfare, temporary facilities and other project running costs.
Programme impact
A variation may extend the project or require work to be completed in a different sequence.
Overheads and profit
Apply the relevant contractual valuation rules and the contractor's commercial pricing policy.
Example: Pricing an additional work request
Suppose a client requests additional flooring work during a commercial refurbishment.
| Cost item | Amount |
|---|---|
| Materials | £3,200 |
| Labour | £1,800 |
| Subcontractor costs | £900 |
| Equipment and delivery | £350 |
| Additional site overheads | £450 |
| Total estimated cost | £6,700 |
If the contractor quotes £7,500, the estimated contribution before any further costs is £800.
However, this calculation is only useful if the estimated costs are realistic and the quoted price is permitted under the contract. The contractor should also consider any programme changes and the risk of further costs.
4. Obtain Proper Approval Before Starting Additional Work
Where the contract requires a formal instruction or approval, the contractor should follow that process rather than relying on informal conversations.
Before starting a variation, the commercial team should ideally establish:
What exactly is changing?
Who has authority to instruct the change?
Is the additional work within the original contract?
How will the change be valued?
Will the completion date be affected?
What supporting records must be provided?
When can the additional amount be included in a payment application?
There may be circumstances where work needs to proceed urgently, particularly for safety or to prevent further damage. In those situations, the contractor should still preserve evidence, record instructions and follow the contractual procedure as soon as reasonably possible.
A written record protects both the contractor and the client by making it easier to understand what was requested and what was actually completed.
5. Keep Evidence of Labour, Materials and Work Completed
A variation quotation should not be the only supporting document.
The contractor should maintain evidence that connects the requested change to the resources used and the work completed.
Useful records include:
Written instructions and approvals.
Revised drawings and specifications.
Site photographs.
Labour allocation sheets.
Timesheets.
Materials invoices.
Delivery notes.
Subcontractor invoices.
Plant hire records.
Site diaries.
Completion and inspection records.
For work valued on a daywork basis, accurate labour, plant and material records can be particularly important.
RICS guidance on valuing change explains how variations are assessed under different standard forms of construction contract. The valuation method and supporting requirements should always be checked against the contract actually in use.
6. Understand the Accounting Treatment of Construction Variations
A contractor should not automatically recognise the full amount of a proposed variation as revenue simply because a quotation has been submitted.
The accounting treatment depends on the contract, the applicable reporting framework and whether the business has an enforceable right to the additional consideration.
For entities applying FRS 102, the revised Section 23 revenue requirements are effective for accounting periods beginning on or after 1 January 2026, unless adopted early.
The revised requirements introduce a model that requires businesses to consider the contract, the promised goods or services, the transaction price and when the relevant performance obligations are satisfied.
Construction contracts may involve variable consideration, including:
Additional work and scope changes.
Performance bonuses.
Delay penalties.
Claims.
Price adjustments.
Incentive arrangements.
Approved but unpriced changes can require particular judgement. Contractors need reliable evidence to support the amount included in the transaction price and should consider whether the relevant accounting requirements are satisfied.
This is one reason why project records should be updated throughout the contract rather than reconstructed at year-end.
7. Include Variations in Payment Applications Correctly
A completed variation may still create a cash-flow problem if it is not included in the correct payment application.
Contractors should reconcile their variation register with the application for payment and supporting project documentation.
The reconciliation should show:
Original contract value.
Approved variations.
Omitted work.
Value of completed work.
Retention deductions, where applicable.
Previous certified payments.
Amount currently claimed.
Amount outstanding.
It is important to distinguish a payment application from a VAT invoice. The contractual payment procedure and VAT tax-point rules should be considered separately.
The contractor should also check the contract's payment notice and pay less notice procedures, as well as the relevant statutory payment provisions.
Accurate construction bookkeeping and financial records help ensure that project costs, supplier invoices, subcontractor payments and customer balances are reflected correctly in the accounting system.
8. Monitor the Impact on Project Gross Profit
A variation can increase contract revenue without necessarily increasing the contractor's profit.
For example, a £15,000 variation may look commercially attractive. However, if the additional labour, materials, subcontractor costs and programme delays total £14,200, the contribution is only £800.
The contractor should review the project margin before and after significant changes.
Useful measures include:
Original estimated project margin.
Revised contract value.
Actual costs incurred.
Cost to complete.
Approved variation value.
Unapproved variation exposure.
Remaining project contingency.
Expected final project profit.
This helps management identify whether a project is becoming less profitable despite an increase in its contract value.
9. Use Monthly Project Reports to Identify Problems Early
A project report should show more than the amount invoiced to the client.
Construction businesses should review the financial position of each active project regularly, particularly where projects involve several subcontractors or significant changes to the original scope.
A useful monthly report may include:
Original contract sum.
Approved changes.
Pending variations.
Work completed.
Revenue recognised.
Costs incurred.
Outstanding supplier invoices.
Certified and uncertified applications.
Customer payments received.
Estimated cost to complete.
Forecast final margin.
Regular management accounts for construction businesses can turn these records into practical information for directors and project managers.
The reports can help identify projects where costs are increasing faster than revenue or where additional work has not yet been properly agreed.
Practical Construction Variation Checklist
Before treating a variation as commercially complete, review the following:
Has the requested change been clearly described?
Has the correct person authorised it?
Have the contract's notification requirements been followed?
Has the cost been calculated in full?
Has the selling price been agreed or properly assessed?
Are labour and material records available?
Has the programme impact been considered?
Has the variation register been updated?
Has the accounting treatment been reviewed?
Has the amount been included in the appropriate payment application?
Has the certified amount been reconciled?
Has the final project margin been updated?
Frequently Asked Questions
What is the difference between a variation and additional work?
Additional work is work beyond the original scope. A variation is a formal contractual change to the agreed work, which may involve additions, omissions or alterations. The precise terminology depends on the contract.
Can a contractor charge for work requested verbally?
A verbal request may be relevant evidence, but the contractor should check the contract's instruction and approval requirements. Relying on verbal conversations alone can create disputes about authority, scope and price.
Should unapproved variations be included in revenue?
Not automatically. Revenue recognition depends on the contractual rights, the applicable accounting framework and the relevant recognition requirements. A submitted quotation alone does not establish that revenue has been earned.
How can contractors reduce variation disputes?
Use a variation register, obtain instructions from authorised representatives, agree valuation methods where possible and retain evidence of the work completed.
Why should construction variations be reviewed monthly?
Monthly reviews help identify unapproved work, rising costs, delayed certification and changes to the expected project margin before they create larger financial problems.
Final Thoughts
Variations are a normal part of construction, but poorly managed changes can turn profitable contracts into difficult projects.
Contractors need a clear process for pricing additional work, obtaining approvals, recording costs and updating their financial forecasts. The objective is to ensure that every significant change is commercially understood and properly supported.
For construction companies in Stanmore, London and across the UK, strong variation controls can improve project visibility, protect margins and reduce unnecessary disputes.
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