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When building work is defective, the usual starting point is the reasonable cost of putting it right. That figure is not automatic. An English court asks what work is necessary, whether the proposed remedy is reasonable and proportionate to the benefit, whether a loss in the property’s value is a better measure, and whether the claimant has taken reasonable steps to limit the loss. In some fact-specific cases, a proven loss of amenity may be recoverable even when market value has not fallen.
The objective is compensation: to place the claimant, financially, in the position they would have occupied if the contract had been properly performed. The evidence and the claimant’s actual interest in the property determine which measure fits.
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The compensatory starting point
Damages for defective construction are normally designed to compensate financial loss flowing naturally from the breach. They are not a punishment for poor workmanship. The accessible extract from Mel Tomlin’s fourth Essential Law article in Building, published on 31 August 2022, states the objective as putting the claimant in the same financial position as if the contract had been performed correctly.
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Repair Windows errors before they cause bigger problemsFix Now →Fix the driver behind crashes, sound loss and screen glitchesFind Drivers →That principle does not mean every expense claimed by an owner is recoverable. The court identifies the loss caused by the defect and selects the measure that most accurately compensates it. The ordinary rule concerns financial loss; the extract notes that non-financial losses such as mental distress are subject to limited exceptions, but the full gated article is not available and its treatment of those exceptions should not be inferred.
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In practice, the court usually compares the cost of a reasonable remedy with the reduction in value caused by the defect, while considering mitigation, alternatives and the claimant’s interest in the property.
Repair or reinstatement cost: the usual measure
Repair or reinstatement cost is commonly appropriate in a claim against a contractor or professional where the expense is the foreseeable consequence of defective work. The Technology and Construction Court described that approach in McGlinn v Waltham Contractors Ltd [2007] EWHC 149 (TCC). It reflects the practical purpose of a building contract: the client bargained for a specified result, so the cost of achieving that result can represent the loss.
A repair claim should be tied to the defect and to work that will actually cure it. A court may reject an estimate that includes upgrades, unrelated refurbishment or a specification materially better than the contract required. The claimant should show both the technical necessity of the proposed scope and its reasonable market price.
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1Clear out junk files and repair common Windows errors2Fix the driver behind crashes, sound loss and screen glitches3Repair Windows errors before they cause bigger problemsWhat a repair-cost claim must establish
- The contractual requirement, drawing, specification or professional duty that was breached.
- The physical defect and the causal link between it and the breach.
- The remedial method that will achieve the promised performance or a technically equivalent result.
- Competitive, properly itemised costs, including access, professional fees and any necessary temporary accommodation or protection of contents.
- That the work is reasonably required rather than merely desirable.
Contemporaneous photographs, inspection reports, design information, correspondence and invoices are more persuasive than a single unexplained total. If the defect has not yet been repaired, obtain evidence before opening up or demolishing work, and preserve samples where appropriate.
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Why a repair bill is not an automatic entitlement
The House of Lords’ decision in Ruxley Electronics & Construction Ltd v Forsyth [1995] UKHL 8 is the leading illustration of the limits on reinstatement cost. Lord Lloyd stated: “As to what remedial work is both ‘necessary’ and ‘reasonable’ in any particular case is a question of fact.” The court therefore examines the circumstances, not just the arithmetic of an estimate.
Necessity
Ask whether the proposed work is needed to remove the functional, safety or contractual deficiency. A claimant who can live with a minor imperfection may still have a claim, but the court will not assume that complete rebuilding is necessary simply because it is technically possible. Evidence should explain the consequences of leaving the defect and why less extensive work would not provide the contracted result.
Reasonableness
Reasonableness covers the method, scope and price. A technically sound alternative may be preferred if it delivers the required performance at materially lower cost. Conversely, a cheaper patch may be unreasonable if it leaves a foreseeable risk or fails to provide a durable remedy. Expert opinions should identify the options considered and explain the assumptions behind each cost.
Proportionality
The expense must bear a reasonable relationship to the benefit obtained. In Ruxley, rebuilding a swimming pool to the specified depth would have cost substantially more than the practical benefit of doing so. The court regarded that reinstatement as unreasonable in the circumstances. Proportionality is not a fixed percentage test; it is a factual assessment of the improvement, the contractual importance of the requirement and the cost of achieving it.
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Diminution in value as an alternative
Diminution in value measures the difference between the property’s value as constructed and its value if the contract had been properly performed. It can be the better measure where reinstatement would be unreasonable, where the claimant does not intend to carry out the work, or where the defect has little effect on market value.
A valuation must isolate the effect of the defect from ordinary market movements and other property features. The valuer should state the date, assumptions and comparable evidence used. If no measurable value difference is proved, the result may be nominal rather than a large repair award; Ruxley explains that the evidence determines the outcome.
When value evidence is especially important
- The proposed repair is radically more expensive than the increase in value it would create.
- The property can be sold or used satisfactorily without the work.
- The claimant has not shown a genuine intention to reinstate.
- The claimant owns only a limited interest rather than the whole beneficial interest.
- A satisfactory replacement or substitute is available elsewhere.
Diminution does not automatically defeat a repair claim. If the contractual performance has personal or practical importance and reasonable reinstatement is shown, repair cost may still be the more accurate measure.
Loss of amenity and personal value
Ruxley involved a pool built shallower than specified. The lower court found no diminution in value and considered rebuilding unreasonable, but awarded £2,500 for loss of amenity. The House of Lords restored that result. The case recognises that market value may not capture every proven consequence of defective performance.
Amenity is fact-specific. It may relate to the enjoyment or use for which the work was commissioned, rather than a general award for disappointment. A claimant must show what use or benefit was lost and why a value-based calculation does not fully represent it. Ruxley is not a guarantee of an additional award whenever workmanship is imperfect.
Mitigation: the claimant’s duty after discovering a defect
Lord Lloyd stated in Ruxley: “The fundamental basis is thus compensation for pecuniary loss naturally flowing from the breach; but this first principle is qualified by a second, which imposes on a plaintiff the duty of taking all reasonable steps to mitigate the loss consequent on the breach”.
Mitigation does not require a claimant to accept an unsafe or inferior solution, nor to fund the contractor’s preferred method. It requires reasonable conduct in the circumstances. Examples include stopping water ingress before secondary damage occurs, arranging temporary protection, obtaining timely advice, and avoiding unnecessary delay once a workable remedy is known.
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A claimant who unreasonably allows damage to grow may recover only the loss that would have remained had reasonable steps been taken. Conversely, a claimant should document why an interim measure was impractical, unsafe or disproportionately expensive. Keep a dated log of notifications, inspections, quotations, temporary works and decisions.
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The claimant’s interest can change the measure
McGlinn emphasises that the claimant’s legal and practical interest matters. Someone with only a limited interest in a property may not be entitled to the cost of rebuilding that benefits a superior owner. Likewise, if the claimant can obtain a satisfactory replacement elsewhere, replacement cost or diminution may describe the actual loss more accurately than rebuilding the original work.
Identify who contracted for the work, who owns the relevant interest, who occupies the property and who will receive the benefit of any remedial work. Lease terms, sale plans, development arrangements and intended use can all affect the analysis. A damages model that ignores those facts risks claiming a remedy for a benefit the claimant will not receive.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Comparing the principal measures
| Measure | Question the court asks | Evidence normally required | Main risk |
|---|---|---|---|
| Repair or reinstatement cost | What work is necessary and reasonable to deliver the contracted result? | Defect diagnosis, remedial design, itemised quotations and expert explanation | Scope may be rejected as excessive, upgrading the property or disproportionate |
| Diminution in value | How much less is the property worth because of the defect? | Independent valuation using stated assumptions and comparable evidence | Loss may be small or unproved even though a defect exists |
| Replacement cost | Can a satisfactory substitute be obtained, and at what reasonable cost? | Evidence of available alternatives, prices and equivalence | A substitute may not provide the same contractual or personal benefit |
| Amenity or personal value | What proven use or enjoyment is missing from a market-value calculation? | Evidence of intended use, actual impact and why value is incomplete | Ruxley is fact-specific; no automatic additional award follows |
A practical method for preparing a defects damages claim
- Define the contractual promise. Assemble the signed contract, scope, drawings, specifications, variations, inspection records and payment documents. Mark the precise requirement said to be defective.
- Record the condition before intervention. Photograph and video the defect, note dates and effects, and obtain an independent inspection. Preserve relevant components and records before opening up.
- Separate defect, consequence and remedy. Ask the expert to identify the breach, the resulting damage and each remedial option. Do not combine unrelated refurbishment with the claim.
- Obtain more than one properly scoped estimate. Quotations should use the same specification so that prices are comparable. Explain access, preliminaries, design fees, taxes and temporary accommodation assumptions.
- Test proportionality. Compare the cost and benefit of each option. Consider durability, safety, contractual importance, effect on use and any increase in property value.
- Obtain valuation evidence where relevant. Request “as is” and “as warranted” valuations, with the defect isolated from market changes and other attributes.
- Analyse alternatives and mitigation. Record temporary measures, replacement possibilities, the claimant’s intentions and reasons for accepting or rejecting proposed solutions.
- Match the claim to the claimant’s interest. Check ownership, lease rights, occupation, planned sale and who will enjoy the repaired work.
- Update the loss schedule. Keep repair costs, professional fees and consequential expenses distinct, supported by receipts and linked to the defect.
What Ruxley does—and does not—decide
Ruxley does not establish a universal cap on construction damages. It demonstrates a sequence of questions: identify the contractual performance, assess the reasonable remedy, compare its cost with the benefit, consider diminution in value, and ask whether a genuine loss remains outside market value. Its swimming-pool award arose from the particular evidence, including the absence of diminution and the importance of the lost amenity.
The judgment also confirms that mitigation is part of the compensatory analysis. A claimant’s conduct after breach can affect the recoverable amount, just as the original defect does.
What McGlinn adds
McGlinn v Waltham Contractors Ltd provides a practical formulation for contractor and professional-negligence claims: repair or reinstatement is usually appropriate when it is the foreseeable consequence of defective work. It also cautions that a limited interest in the property or a satisfactory replacement elsewhere may make diminution or replacement cost the more accurate measure. The case supports analysing the claimant’s real loss rather than applying repair cost mechanically.
Limits of the published 2022 overview
The fourth Essential Law instalment in Building is dated 31 August 2022 and is presented as an explanation of how damages for defects are assessed. Its accessible extract supports the compensatory principle and indicates that the article discusses exceptions concerning non-financial loss. Because the full article is gated, no further article-specific proposition should be attributed to it. The legal propositions above come from the cited judgments and remain dependent on the facts, evidence and applicable procedural rules of the individual claim.
Bottom line
Start with reasonable repair cost, but prove why the work is necessary, reasonable and proportionate. Test that figure against diminution in value, replacement possibilities, mitigation and the claimant’s actual interest. Where market value misses a real loss of use or enjoyment, Ruxley shows that amenity may matter. A defensible damages claim is therefore an evidence-led comparison of measures, not an automatic demand for the largest contractor’s estimate.
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