Renovation contingency budgets: plan for the unknowns
Build a sensible allowance for hidden defects and avoid treating provisional sums as fixed prices.
Applies to: UK homeowners; no single contingency percentage suits every project.
Last checked: 16 October 2026
Key points
• Older buildings and disruptive work often reveal conditions that could not be seen at quoting stage.
• Separate confirmed prices, provisional allowances and genuinely optional upgrades.
• Approve extra work and cost changes in writing before proceeding where practical.
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Why it matters
Removing a kitchen, lifting flooring or opening walls can reveal damaged services or unsound substrates. These uncertainties cannot always be priced honestly before opening up.
Checklist before you start
• Ask each contractor to identify known assumptions and unresolved risks.
• Hold a contingency outside the agreed contract sum rather than spending it on finishes.
• Require evidence, options and a written variation for unforeseen work.
• Keep VAT, waste, temporary facilities and professional fees in the overall budget.
What to do next
A contingency is a planning cushion, not permission for unlimited extra charges. Review the remaining budget against every approved change and unfinished stage.
Official sources
Use these official sources for the current detail that applies to your job, contract or location.
BuildPair provides general information and signposting, not legal, structural, electrical, gas or building-control approval. Requirements can change and the right answer depends on the work, contract, location and facts.
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