A refurbishment budget can look profitable on paper and still fail the moment the first wall is opened. Damp behind dry lining, an obsolete consumer unit, rotten floor joists or a missing Building Control record can each turn a modest scope change into a material cost. To calculate refurbishment contingency properly, start with the condition of the building, not a percentage copied from the last deal.
For developers, landlords and capital partners, contingency is not spare money to make a spreadsheet feel safer. It is a controlled allowance for defined uncertainty. It protects programme, finance costs and exit margin when genuine unknowns emerge. Used carelessly, it can hide weak pricing. Used well, it is evidence that the deal has been assessed with discipline.
What refurbishment contingency is, and is not
A contingency is a provision for works that are plausible but cannot be fully quantified at the point of appraisal. It sits separately from the priced base scope, professional fees, finance costs and a developer's profit. If a new kitchen, bathroom, rewire or roof repair is clearly required, those items belong in the main works budget. They are not contingency simply because the final quotation has not yet been agreed.
Nor should contingency become a catch-all for poor cost control. Variations caused by changing the specification halfway through a project, upgrading finishes beyond the investment case or failing to instruct trades clearly are management issues. They should be prevented through scope control, not absorbed without challenge.
The real question is: what could reasonably be discovered, required or disrupted after acquisition that is not yet reflected in the base cost plan? The answer depends on the asset, the evidence available and the delivery strategy.
Start with a surveyed and priced base scope
A percentage is only meaningful after the underlying refurbishment cost has been built properly. Before setting contingency, establish a measured scope of works based on a detailed inspection, dimensioned floorplans, photographs and trade input. For more complex assets, this may need a building survey, drainage investigation, asbestos survey, electrical inspection or structural engineer's review.
Break the budget down by work package. Demolition, strip-out, structural works, roofing, windows, damp treatment, plumbing, electrical works, plastering, kitchens, bathrooms, finishes and external works should each be visible. This makes omissions easier to identify and allows the team to see where risk is concentrated.
A single builder's figure may be useful, but it is not sufficient evidence on its own. Check whether it includes waste removal, scaffolding, temporary protection, making good, certification, preliminaries, VAT where applicable and access constraints. A low quote with major exclusions does not reduce risk. It transfers risk into contingency, often without anyone acknowledging it.
How to calculate refurbishment contingency from risk
The practical calculation is straightforward:
Contingency allowance = priced refurbishment cost x risk percentage
The judgement lies in setting the risk percentage. On a well-surveyed, modern flat with a cosmetic specification and firm trade quotations, 5% may be sufficient. On an older house with signs of water ingress, incomplete services information and substantial strip-out, 10% to 15% may be more appropriate. A project involving structural alteration, change of use, heritage constraints or significant unknown ground conditions can justify a higher allowance, or a separate risk provision for the specific exposure.
Do not apply one percentage blindly across every line item. A £25,000 kitchen and bathroom package with a fixed specification may carry relatively little uncertainty once ordered. A £20,000 allowance for roof repairs following a ground-level inspection may carry much more. A more accurate approach is to assess each uncertain package, then aggregate the allowances.
For example, consider a Victorian terrace with a £90,000 base refurbishment budget. The visible works include reconfiguration, a new heating system, full electrical upgrade, kitchen, bathroom, plastering and decoration. During inspection, the rear roof covering appears tired, moisture readings are elevated around the chimney breast, and suspended timber floors cannot be inspected fully.
Rather than adding 10% to every item without explanation, the appraisal might include £3,500 for potential roof timber and chimney repairs, £2,500 for concealed floor repairs, £2,000 for damp-related making good and £1,000 for services diversions or compliance items. That produces a £9,000 contingency, equivalent to 10% of the base works cost. The figure is traceable to observed risks, which makes it easier to review before exchange and manage during delivery.
Factors that should increase the allowance
The age and construction of the building matter. Period properties can contain concealed defects, non-standard details and alterations completed to uncertain standards. Solid-wall construction, old roof structures, suspended floors, basements and historic extensions all need careful investigation. The issue is not that older stock is uninvestable. It is that the evidence threshold should be higher.
Access and occupation also affect risk. A third-floor flat with no lift, restricted parking and leaseholder rules will cost more to deliver than a vacant house with clear access. Occupied properties may require phased work, careful welfare arrangements and a greater allowance for delay. In leasehold blocks, check licences to alter, freeholder requirements, service charge arrears and restrictions on working hours before relying on a short programme.
Services are a frequent source of budget pressure. Electrical installations may require a full rewire rather than partial remedial work. Old pipework can fail when new sanitaryware is fitted. Heating upgrades can expose inadequate gas supply, poor water pressure or unplanned remedial work to flues. Where evidence is weak, budget for investigation before commitment where possible.
Planning and Building Regulations risk must also be separated from physical defects. If the value-add strategy depends on a rear extension, loft conversion or material internal alteration, do not treat consent as a footnote. Allow adequately for design, statutory requirements, party wall matters, structural details and time. A contingency pot cannot repair a flawed planning assumption.
Protect the programme as well as the works budget
Cost contingency is only half the calculation. Delays have a financial consequence through interest, utilities, insurance, council tax, security and lost rental or sale opportunity. A project funded with short-term finance needs a programme contingency as well as a works contingency.
Build a realistic programme around critical dependencies: surveys, design decisions, ordered materials, structural works, first fix, inspections, second fix and certification. Then stress-test it. If a roof defect adds three weeks, or a replacement window lead time slips, what does that do to the finance period and planned exit?
This is particularly relevant when margins are narrow. A £7,500 works contingency may appear adequate, yet a two-month finance extension and delayed sale could consume substantially more value. The appraisal should show both figures separately so that the acquisition decision reflects the full downside.
Control contingency after purchase
Contingency should not disappear into the main account once the keys are collected. Hold it as a separate line within the project cost report. Every drawdown should be recorded against a specific issue, with photographs, quotations, an explanation of cause and approval by the person accountable for the project budget.
Early strip-out is the point at which uncertainty should reduce sharply. Once floors, ceilings and boxing are opened, revisit the risk register and reforecast the final cost. If expected defects have not appeared, retain the unused allowance rather than finding cosmetic ways to spend it. If they have appeared, decide whether to repair, redesign or revise the exit strategy before the overrun becomes irreversible.
For joint ventures and investor-backed projects, this discipline is also a governance requirement. Partners should be able to distinguish between the agreed base scope, approved variations and contingency deployment. Clear records protect relationships when a project encounters genuine building risk.
The margin must survive the downside case
A sensible appraisal tests more than the expected refurbishment cost. Run a downside case that includes full contingency use, a modest programme delay and a conservative sale price or refinance valuation. If the projected return only works when every assumption is favourable, the deal is not priced for control.
There is no universal contingency percentage because buildings do not carry universal risk. The right figure comes from inspection quality, construction knowledge, scope definition and the commercial consequences of delay. A smaller, documented allowance on a well-understood project is stronger than a large, arbitrary buffer on one that has not been properly investigated.
The most useful closing question before committing is simple: if the contingency is fully spent, does the project still meet the required return? If the answer is no, either reduce the purchase price, reduce the risk before exchange or leave the opportunity alone.