Contracts, Variations, Valuation and Payments

Introduction

Construction estimating does not end when a tender is accepted. During execution, the quantity of work may change, prices may fluctuate, defects may require correction, and payments must be assessed against measured progress. Contract administration provides the system through which these changes are controlled and the contractor is paid fairly.

A construction contract establishes the rights and obligations of the client, contractor, consultant and, where applicable, subcontractors. It normally defines the scope of work, contract price, completion period, quality requirements, measurement rules, payment procedures, variations, claims, retention, insurance, extension of time, dispute resolution and completion requirements. Although contract forms differ between countries and institutions, the underlying estimating and costing principles are broadly similar.

This chapter explains how an estimator or quantity surveyor applies contract provisions to completed work, variations, escalation, retention, claims, final accounts, depreciation and property valuation.

Learning Objectives

After studying this chapter, the learner should be able to:

1. Explain the purpose and essential elements of a construction contract.
2. Distinguish between interim valuation, interim certificate and payment.
3. Measure completed work and calculate the gross value of work executed.
4. Price variations using appropriate contractual methods.
5. Apply retention, advance-payment recovery, deductions and escalation provisions.
6. Identify the basic requirements for a claim and final account.
7. Explain depreciation and the principal approaches to property valuation.
8. Maintain transparent, ethical and properly documented contract records.

1. Construction Contracts and Contract Administration

1.1 Meaning and purpose

A construction contract is a legally enforceable agreement under which one party undertakes to execute specified construction work for another party in return for an agreed price or a price determined by an agreed mechanism. The contract converts the design and tender information into enforceable obligations.

Contract administration is the practical management of those obligations. It includes issuing instructions, recording progress, measuring work, assessing payment, controlling changes, maintaining records, managing time and cost, and closing the contract.

1.2 Essential contract documents

A typical contract may contain:

• agreement or letter of acceptance;
• conditions of contract, including general and special conditions;
• drawings and specifications;
• bill of quantities or schedule of prices;
• programme and completion requirements;
• pricing and payment provisions;
• securities, bonds and insurance requirements;
• schedules of rates, material schedules and method statements; and
• addenda and written clarifications issued before award.

The order of precedence is important when documents conflict. It must be stated in the contract. An estimator should never assume that a drawing automatically overrides a specification or bill of quantities.

1.3 Common pricing arrangements

No pricing arrangement removes the need for proper measurement and records. Even a lump-sum contract requires valuation of variations, completed work, omitted work and sometimes sectional completion.

1.4 Roles of the principal parties

The client provides the project requirement, makes payments and gives access to the site. The contractor executes the work, supplies resources and complies with the contract. The contract administrator, architect, engineer or quantity surveyor administers the contract according to the authority granted. The administrator must act fairly, use the stated valuation rules and keep an auditable record.

A contract administrator should distinguish between a formal instruction and an informal discussion. Site conversations may assist coordination, but a change affecting price or time should be confirmed in writing.

2. Measurement of Completed Work

Measurement converts physical progress into quantities that can be valued. The work must be measured according to the contract’s method of measurement. Common units include cubic metres for concrete and excavation, square metres for plastering and formwork, metres for pipework, kilograms or tonnes for reinforcement, and items or sums for defined installations.

2.1 Principles of measurement

Good measurement is:

• accurate: dimensions correspond to actual work;
• consistent: the same rules are applied throughout;
• verifiable: another person can reproduce the result;
• traceable: each quantity is linked to drawings, records or inspection evidence; and
• contract-compliant: inclusions, deductions, laps, waste and tolerances follow the specified rules.

Measurements may be obtained from site measurement books, approved drawings, inspection records, delivery records, photographs, digital models and jointly signed measurement sheets. A quantity should not be certified merely because materials are present on site unless the contract permits payment for stored materials and the required ownership, protection and insurance conditions are satisfied.

2.2 Gross value of work executed

For measured work, the basic valuation is:

where:

• V_w = value of work executed;
• Q_i = measured quantity of work item i;
• R_i = applicable contract rate for item i; and
• the summation includes all measured items.

The formula assumes that the rate includes all components specified by the contract, such as labour, materials, plant, overheads and profit. It is applicable where payment is based on measured quantities and stated rates. Units must be compatible: for example, a quantity in m² multiplied by a rate in currency/m² produces a value in currency.

For a lump-sum activity valued by percentage progress:

where V_a is the value of the activity completed, P_a is the assessed fraction of completion expressed as a decimal, and W_a is the accepted value of the activity. The percentage must be supported by measurable progress; it must not be used to conceal unperformed work.

2.3 Example: measurement and interim value

A contractor executes the following work:

Thus, V_w = 2520 + 4620 + 8320 = 15460 currency units. This is the gross value before considering previous certificates, retention, advances, variations, taxes or other deductions.

3. Interim Valuations and Payments

An interim valuation determines the value earned up to a valuation date. An interim payment certificate, issued by the authorised contract administrator, states the amount that is payable under the contract. The certificate is not necessarily the same as the contractor’s application.

A typical valuation statement is:

where:

• P_n = net amount certified for the current period;
• V_c = value of measured work completed to date;
• V_m = value of approved materials or goods eligible for payment;
• V_v = value of approved variations;
• V_e = approved escalation or other contractual adjustment;
• A_c = approved claims or additions;
• R = retention deduction;
• A_r = recovery of advance payment;
• D = other authorised deductions, such as contra-charges or taxes; and
• P_p = amounts previously certified.

The equation is a general framework, not a universal certificate format. The contract may include taxes, provisional sums, nominated subcontractors or other items separately. Each component must be supported by the relevant clause and records.

3.1 Retention

Retention is a percentage withheld from certified amounts to provide security for completion and correction of defects. If the retention rate is r and the retention base is B, then:

Here, r is expressed as a decimal, such as 0.05 for 5%. The contract may specify a maximum retention limit and may provide for partial release at practical completion and final release after the defects liability period.

Retention is not a penalty. It is contract security and must be released according to the stated conditions. Unauthorised withholding can constitute a payment dispute.

3.2 Advance payment and recovery

An advance payment provides early cash flow for mobilisation or procurement. It is normally secured by an advance-payment guarantee and recovered progressively. If the recovery rate is a and the applicable base is B_a, the recovery is:

The contract must identify the base and the point at which recovery begins. Applying a percentage to the wrong base is a common valuation error.

3.3 Numerical example: interim certificate

Suppose the current valuation includes:

• measured work to date: 15,460;
• approved materials: 2,000;
• approved variation: 1,200;
• no escalation or claim;
• retention: 5% of the gross eligible value;
• advance recovery: 10% of the measured work value;
• previous certificates: 12,000.

The gross eligible value is:

B = 15460 + 2000 + 1200 = 18660

Retention is:

R = 0.05 × 18660 = 933

Advance recovery is:

A_r = 0.10 × 15460 = 1546

The net current certificate is:

P_n = 18660 − 933 − 1546 − 12000 = 4181

Therefore, the amount certified for the current period, before any taxes or additional deductions required by the contract, is 4,181 currency units.

4. Variations and Change Control

A variation is an authorised change to the scope, quantity, quality, sequence or method of work. Examples include additional excavation, revised finishes, a changed foundation detail, omission of a wall, or a change in material specification.

A variation is not simply any difference between the contractor’s expectation and the actual situation. It must arise under the contract and be instructed or otherwise recognised through the contractual procedure.

4.1 Types of variation

• Addition: new work is introduced.
• Omission: work is removed from the contract.
• Substitution: one specified material or method is replaced by another.
• Change in quantity: the quantity differs from the bill quantity.
• Change in quality or design: performance or specification is altered.
• Provisional-sum expenditure: work is defined and valued after details become available.

4.2 Valuation hierarchy

The contract normally establishes a hierarchy:

1. use an existing rate where the work is of similar character and carried out under similar conditions;
2. use an existing rate with a justified adjustment where conditions differ;
3. derive a new rate from labour, material, plant, overhead and profit components; or
4. agree a lump sum or daywork valuation where measurement is impracticable.

A new rate should be supported by resource build-ups, supplier quotations, labour records, plant logs and agreed overhead and profit percentages. A quotation alone is not necessarily a contractual rate.

4.3 Variation procedure

A disciplined procedure is:

1. identify the need for change;
2. issue a clear written instruction or obtain contractual authorisation;
3. record the effect on quantity, price, quality and time;
4. obtain drawings, specifications and quotations where required;
5. agree or determine the rate;
6. execute and measure the work; and
7. include the assessed amount in the appropriate valuation and final account.

Work carried out without required authorisation may be difficult to recover, even if it benefits the project. Emergency provisions may apply where immediate action is necessary to protect life or property, but the contractor should notify the administrator promptly.

4.4 Variation example

A bill rate for ordinary blockwork is 32 currency/m². A variation requires 50 m² of similar blockwork under comparable conditions. The variation value is:

V_v = 50 × 32 = 1600 currency units.

If the variation instead requires a different block and additional labour, the existing rate should not be used automatically. A resource build-up may produce a new rate, for example:

The value for 50 m² would then be 2,050 currency units, subject to contractual approval and the stated basis of calculation.

5. Price Escalation and Fluctuation

Escalation compensates for changes in the cost of labour, materials, fuel or other inputs when the contract allows adjustment. A fixed-price contract does not automatically entitle the contractor to escalation; the entitlement must arise from the contract or applicable law.

A simple index-based adjustment may be expressed as:

where:

• A_e = escalation adjustment;
• V_b = eligible base value of work;
• w_L, w_M, w_F, w_O = contractual weights for labour, materials, fuel and other components;
• L₀, M₀, F₀ = base-date indices;
• L_t, M_t, F_t = indices at the valuation date; and
• the weights sum to 1.

The formula assumes that the contract specifies representative indices, base dates, eligible work, weights and treatment of negative movements. If the weights sum to 1, the bracketed expression represents the proportional change in the weighted cost basket. For example, with weights 0.30, 0.40, 0.10 and 0.20, and index ratios 1.10, 1.08, 1.20 and 1.00:

0.30(1.10) + 0.40(1.08) + 0.10(1.20) + 0.20(1.00) = 1.092

The escalation is therefore 9.2% of the eligible base value. If V_b = 10000, then A_e = 10000 × 0.092 = 920 currency units.

Escalation clauses often exclude variations, delayed work attributable to the contractor, imported items or work completed after the contractual date unless an extension of time is granted. The exact clause must be followed.

6. Claims, Extensions of Time and Disputes

A claim is a request for contractual entitlement, commonly involving additional payment, additional time or both. Typical causes include late possession of site, delayed information, unforeseen physical conditions, employer changes, suspension, abnormal weather or disruption.

A sound claim establishes:

1. entitlement: the contract clause or legal basis;
2. cause: the event that occurred;
3. notice: timely notification in the required form;
4. effect: the demonstrable delay, disruption or cost;
5. records: contemporaneous evidence; and
6. quantum and time: a reasoned calculation of money and days.

The basic claim relationship is not simply “event occurred, therefore payment is due.” The claimant must connect the event to the actual loss or delay and avoid double recovery.

Useful records include programmes and updates, daily reports, labour and plant returns, delivery tickets, correspondence, photographs, instructions, weather data, meeting minutes and cost ledgers. A claim should distinguish direct cost from overhead, prolongation, disruption and loss of productivity, because contractual treatment may differ.

An extension of time protects the contractor from damages for late completion where delay is caused by an employer-risk event or another compensable cause. It does not automatically establish monetary entitlement. Time and money must be analysed under the relevant provisions.

Disputes should be managed progressively through discussion, determination, negotiation, mediation, adjudication, arbitration or litigation, depending on the contract and applicable law. Early escalation of every disagreement is inefficient; ignoring a serious dispute is equally dangerous.

7. Final Account and Contract Close-Out

The final account establishes the final amount due after completion, measurement, variations, claims and corrections have been resolved. It should be based on the contract rather than on an informal compromise unless a formal settlement has been approved.

A final account commonly includes:

• original contract sum;
• remeasured quantities;
• additions and omissions;
• approved variations;
• provisional sums and nominated work;
• fluctuation or escalation adjustments;
• approved claims;
• deductions and contra-charges;
• retention and advance-payment status;
• taxes and statutory deductions; and
• amounts previously paid.

The final balance may be represented generally as:

where F is the final amount due, C₀ is the original contract sum, ΔQ is the net remeasurement adjustment, V is the net variation value, E is escalation, C_l is approved claim value, D is deductions, and P is amounts previously paid. This is a framework; taxes, retention and other sums may be displayed separately.

Close-out also requires as-built drawings, operation and maintenance manuals, test certificates, warranties, release of claims where applicable, confirmation of defects correction and release of securities. Records should be archived in accordance with organisational and legal requirements.

8. Depreciation in Construction and Property Costing

Depreciation is the systematic allocation of the depreciable amount of an asset over its useful life. It reflects consumption of service potential through use, age, obsolescence or deterioration. It is not necessarily the same as market-value reduction.

The depreciable amount is:

where D_a is depreciable amount, C is depreciable cost, and S is estimated residual value.

Under straight-line depreciation:

where D_y is annual depreciation and n is useful life in years. The method assumes approximately even consumption of service potential.

For an asset costing 50,000 currency units, with residual value 5,000 and useful life 9 years:

D_y = (50000 − 5000)/9 = 5000 currency units per year.

The carrying amount after t full years under straight-line depreciation is:

subject to not falling below the residual value and subject to the applicable accounting policy.

Other methods include reducing balance and units of production. The selected method should reflect the pattern of consumption and comply with applicable accounting standards. Depreciation for accounting does not by itself determine insurance value, replacement cost or market value.

9. Principles of Property Valuation

Property valuation estimates the value of an interest in land or buildings for a specified purpose, date and basis. The purpose may be sale, lending, taxation, insurance, acquisition, compensation, rent review or financial reporting. A valuation is incomplete unless its purpose, valuation date, assumptions and definition of value are clear.

9.1 Market comparison approach

The market approach compares the subject property with recently transacted comparable properties. Adjustments may be made for location, size, age, condition, access, tenure, services and time of sale. The reliability of the result depends on the quality and comparability of evidence.

9.2 Cost approach

The cost approach considers land value plus the current cost of replacing or reproducing improvements, less depreciation and obsolescence:

where V_c is indicated value by the cost approach, V_l is land value, C_n is new replacement or reproduction cost, and D is total depreciation and obsolescence. The approach is useful for special-purpose buildings and relatively new improvements, but depreciation assessment can be difficult.

9.3 Income or investment approach

For an income-producing property, capitalisation may be used:

where V_i is indicated investment value, NOI is stabilised net operating income per year, and y is the capitalisation yield expressed as a decimal. If net operating income is 24,000 currency units per year and the yield is 0.08, then V_i = 24000/0.08 = 300000 currency units.

The method assumes that income is stabilised and that the selected yield reflects risk, growth expectations, lease conditions and market evidence. It should not be applied mechanically when income is irregular or the property is owner-occupied without a reliable rental basis.

9.4 Highest and best use

Where legally permissible and financially feasible, the value may be influenced by the use that produces the highest value. Planning restrictions, physical constraints, environmental requirements and development costs must be considered. A valuer must not assume a more intensive use merely because it appears profitable.

10. Applied Case: Community Health Centre Contract

The following is an illustrative case, not a report of an actual project.

Background

A community health centre is being constructed under a remeasurement contract. The original contract sum is 480,000 currency units. The contract provides for 5% retention, recovery of a mobilisation advance at 10% of measured work, written instructions for variations, and index-based escalation. The defects liability period is twelve months.

Problem

At the fourth interim valuation, the measured work to date is 172,000. Approved materials eligible for payment total 18,000. A written instruction adds 40 m² of partitioning at an agreed rate of 45 currency/m². The contract administrator must calculate the certificate amount and identify the records needed for future finalisation.

Analysis and solution

The variation value is:

V_v = 40 × 45 = 1800

The gross eligible value is:

B = 172000 + 18000 + 1800 = 191800

Retention is:

R = 0.05 × 191800 = 9590

Advance recovery is based on measured work:

A_r = 0.10 × 172000 = 17200

Assume previous certificates total 150,000 and no escalation, tax or other deduction is included in this simplified illustration. The current amount is:

P_n = 191800 − 9590 − 17200 − 150000 = 15010

The administrator should attach the signed measurement sheets, approved variation instruction, material invoices and storage evidence, updated variation register, advance-recovery statement and retention ledger. The partitioning should be separately identified in the final account, while the quantity of all work should eventually be remeasured in accordance with the contract.

Outcome and learning points

The case demonstrates that a certificate is a controlled financial statement rather than a simple percentage of the contract sum. The same work must not be valued twice, and every addition must be linked to an instruction or contractual entitlement. Proper registers reduce the risk of omitted variations, excessive payment and disputes at final account stage.

11. Professional Practice, Ethics and Technology

Contract valuation requires impartiality. A professional must not inflate quantities, certify defective work knowingly, conceal a variation, backdate an instruction or accept an improper benefit. Conflicts of interest should be disclosed, and confidential tender and payment information should be protected.

Digital measurement and building information modelling can link quantities to drawings and work packages. Mobile applications can capture photographs, location, date and approval status. Document-management systems improve version control and audit trails. Artificial intelligence may assist with quantity extraction, anomaly detection or document classification, but outputs require professional checking because drawings may be ambiguous and contractual interpretation cannot safely be delegated without review.

Good practice includes:

• maintain a variation, claim, payment and retention register;
• use approved document numbering and revision control;
• separate measured work, materials, variations and claims;
• record assumptions and exclusions in every valuation;
• reconcile the certificate with the cost report and ledger;
• obtain approvals before committing the client;
• preserve contemporaneous records; and
• review the contract before applying a familiar formula from another project.

Challenges and Limitations

Contract administration is affected by incomplete designs, inconsistent documents, delayed instructions, poor site records, changing market conditions and differing interpretations of contract clauses. Measurement can also be difficult where work is concealed before inspection. Index-based escalation may not reflect the contractor’s actual procurement costs, while market valuation may be unreliable where comparable transactions are scarce.

The formulas in this chapter are therefore tools within a contractual and professional framework. They do not replace the contract, applicable legislation, accounting standards, valuation standards or expert judgment. In practice, the governing contract and local legal requirements must always be consulted.

Chapter Summary

Construction contracts establish the obligations, pricing rules and procedures that govern project delivery. Interim valuation converts measured progress and eligible materials into a gross value, after which retention, advance recovery, previous certificates and other authorised deductions are applied. Accurate measurement must be consistent, traceable and compliant with the specified method of measurement.

Variations require contractual authority, clear records and suitable pricing. Existing rates may be used only where the work and conditions are comparable; otherwise, a justified new rate or agreed valuation is required. Escalation applies only where the contract permits it and normally uses specified indices, weights and base dates.

A valid claim demonstrates entitlement, causation, notice, effect, records and quantified time or money. The final account reconciles the original sum with remeasurement, variations, escalation, claims, deductions and previous payments. Depreciation allocates depreciable cost over useful life, while property valuation may use market comparison, cost or income approaches according to the purpose and evidence available. Ethical conduct, transparent records and careful use of digital tools are essential to reliable contract administration.

Key Terms

Contract: A legally enforceable agreement creating rights and obligations.

Contract administrator: The authorised person or organisation administering the contract.

Interim valuation: Assessment of the value earned up to a stated valuation date.

Interim payment certificate: An authorised statement of the amount payable for a payment period.

Retention: A contractual amount withheld as security for completion and defects correction.

Advance payment: Money paid early to assist mobilisation or procurement, normally recovered later.

Variation: An authorised change to scope, quantity, quality, sequence or method.

Provisional sum: An allowance for work whose details or quantity are not sufficiently defined at tender.

Escalation: A contractual adjustment for changes in specified cost indices.

Claim: A request for contractual entitlement to time, money or another remedy.

Extension of time: An adjustment to the completion date for an allowable delay.

Final account: The agreed or determined final financial statement of the contract.

Depreciation: Systematic allocation of an asset’s depreciable amount over its useful life.

Residual value: Estimated value of an asset at the end of its useful life.

Market comparison approach: Valuation based on evidence from comparable transactions.

Cost approach: Valuation based on land value plus replacement or reproduction cost less depreciation.

Income approach: Valuation based on capitalised or discounted future income.

Capitalisation yield: Rate used to convert stabilised net income into an indicated value.

Review Questions

Short Answer Questions

1. What is the purpose of an interim valuation?
2. State two requirements for a properly supported variation.
3. What is retention, and why is it withheld?
4. Name four types of records that may support a construction claim.
5. Distinguish between depreciation and market-value reduction.

Long Answer Questions

1. Explain the procedure for measuring and certifying completed work under a remeasurement contract.
2. Discuss the hierarchy for pricing variations and explain why an existing rate may not always be appropriate.
3. Explain the components normally included in an interim payment statement.
4. Describe the preparation and importance of a final account.
5. Compare the market comparison, cost and income approaches to property valuation.

Analytical / Application Questions

1. A valuation contains measured work of 86,000, eligible materials of 9,000 and an approved variation of 3,000. Retention is 5%, advance recovery is 10% of measured work, and previous certificates total 70,000. Calculate the current amount before tax and explain each deduction.
2. A contractor claims additional cost because a revised drawing was issued late. Identify the evidence needed to establish entitlement, causation, delay and quantum.
3. A proposed variation uses a different material and requires special installation conditions. Explain whether the original bill rate should be used and develop a suitable procedure for establishing a new rate.

Multiple Choice Questions with Answers

Question 1

What is the primary purpose of an interim valuation?

A. To determine the final market value of the property

B. To assess the value of work and eligible items up to a valuation date

C. To replace the construction contract

D. To calculate annual depreciation

Correct Answer: B. To assess the value of work and eligible items up to a valuation date

Question 2

Which document normally provides the basis for measuring completed work?

A. A contractor’s informal verbal estimate

B. The applicable contract method of measurement

C. A bank statement alone

D. A property insurance schedule

Correct Answer: B. The applicable contract method of measurement

Question 3

A measured quantity is 60 m² and the applicable rate is 25 currency/m². What is the value?

A. 85 currency units

B. 1,200 currency units

C. 1,500 currency units

D. 2,500 currency units

Correct Answer: C. 1,500 currency units

Question 4

If the retention rate is 5% and the retention base is 20,000 currency units, the retention is:

A. 100 currency units

B. 500 currency units

C. 1,000 currency units

D. 4,000 currency units

Correct Answer: C. 1,000 currency units

Question 5

Which is normally the first pricing preference for a variation of similar work under similar conditions?

A. An existing applicable contract rate

B. A completely unrelated market rate

C. The contractor’s highest quotation

D. The original contract total divided by project duration

Correct Answer: A. An existing applicable contract rate

Question 6

Which item is essential to a well-supported contractual claim?

A. A verbal statement without records

B. Entitlement, cause, effect and supporting evidence

C. A request made only after final payment

D. An assumption that all delay is compensable

Correct Answer: B. Entitlement, cause, effect and supporting evidence

Question 7

Under straight-line depreciation, an asset costs 30,000, has a residual value of 3,000 and a useful life of 9 years. What is annual depreciation?

A. 2,000 currency units

B. 3,000 currency units

C. 3,333 currency units

D. 27,000 currency units

Correct Answer: B. 3,000 currency units

Question 8

Which valuation approach capitalises stabilised net operating income?

A. Market comparison approach

B. Cost approach

C. Income approach

D. Residual quantity approach

Correct Answer: C. Income approach

Question 9

A final account normally includes which of the following?

A. Only the original contract sum

B. Original sum, remeasurement, variations, claims, deductions and previous payments

C. Only unpaid supplier invoices

D. Only the cost of land

Correct Answer: B. Original sum, remeasurement, variations, claims, deductions and previous payments

Question 10

What is the principal ethical requirement when certifying construction work?

A. Certify the largest possible amount

B. Certify work impartially and on the basis of contract and evidence

C. Avoid recording variations

D. Use estimates without checking site progress

Correct Answer: B. Certify work impartially and on the basis of contract and evidence