A contingency figure can make a development appraisal look reassuring. Until the first unexpected cost arrives.
The useful question is what your allowance actually covers. An occupied refurbishment with concealed structure has different uncertainties from a well-investigated site with a coordinated design. Giving both the same percentage does little to explain the exposure.
For property developers, a sensible contingency starts with a list of risks and the information still missing.
Put the unknowns on paper
Ask your project team to identify the issues that could change the scope, cost or programme. Depending on the site, these might include existing foundations, drainage routes, ground conditions, utility capacity or access restrictions.
Record what is known, what remains uncertain, who will investigate it and when a decision is needed. Avoid treating every risk as equally likely or equally expensive.
A drainage survey, for example, may clarify a route that would otherwise remain an assumption in the design. Investigations cost money, but they can allow the team to replace an uncertain allowance with a more informed decision. They cannot remove every hidden condition.
Separate uncertainty from unfinished decisions
A kitchen you have not selected is different from an unforeseen defect behind an existing wall.
Known work should be included in the cost plan, even if the final specification is pending. Identify provisional allowances clearly and test whether they reflect the intended quality. Keep elective upgrades visible rather than allowing them to consume the reserve for genuine uncertainty.
Also check the budget's basis. Does it include professional fees, statutory charges, tax where applicable, finance and external works? A contingency cannot correct a budget that omitted whole categories of expenditure.
Check who carries each risk
Your own reserve, the contractor's pricing allowances and the lender's required contingency may cover different things.
Ask your quantity surveyor or cost adviser to explain the distinctions. Your contractual position also matters: a fixed contract sum does not automatically mean every possible change is included.
Keep a record of the assumptions behind the allowance and the circumstances in which it may be used. Before authorising expenditure, understand what it leaves available for the remaining work.
Review the reserve as the project develops
Update the risk review after surveys, design coordination and procurement, then throughout construction. Some uncertainties will reduce. Others may emerge as work progresses.
Avoid releasing the entire remaining reserve because the early stages went smoothly. Later connections, commissioning and completion work can still carry costs and timing risks.
The right allowance is project-specific and should be reviewed with your cost and finance advisers. There is no single percentage that makes every development safe.
If you are preparing a development in London or Essex, contact Horizon Architecture to discuss an architectural scope that identifies design information gaps before tender.
