My renovation estimates have been wrong in the same ways repeatedly — not because I miss the obvious costs, but because the less obvious ones accumulate.
Renovation projects exceed budget with such regularity it's practically a law of nature. Ask any architect, contractor or homeowner who has renovated and they'll say the final cost was higher than expected. Some of this is genuinely unavoidable — you can't see inside walls until you open them. But a significant portion comes from failing to account for entirely foreseeable costs.
Start With a Complete Scope
Before any numbers, write a complete scope of work. "Renovate the kitchen" is not a scope. A scope lists every task: strip out units, replace electrical circuits, install new flooring, replaster, install new units, plumb new sink position, redecorate. Only with a complete scope can you estimate accurately. Our area calculator establishes room dimensions underpinning material quantities. Our paint calculator and tile calculator produce accurate material amounts.
Labour Costs — The Bigger Number
Labour typically accounts for 40-60% of total renovation cost. 2025/26 day rates in the UK: builder £250-£400 | electrician £300-£450 | plumber £280-£450 | plasterer £250-£400 | tiler £250-£400. If a quote seems very cheap, ask whether the time estimate is realistic for the scope — it often isn't.
Costs People Forget
- Skip hire: clearing a kitchen or bathroom creates substantial waste. Budget £200-£400 per skip.
- Building regulations approval: structural work and new electrical circuits often need sign-off. Fees £200-£500.
- Party wall agreements: any work affecting a shared wall requires a Party Wall Notice. If a formal agreement is needed: £700-£1,500 per surveyor.
- Temporary accommodation: a full kitchen renovation takes 2-4 weeks. Factor in eating out or staying elsewhere.
- Snagging and making good: the final 5-10% of a project always takes longer than expected.
The Contingency Rule
Add minimum 10% contingency for straightforward work; 20% for projects involving older properties or structural work. Opening walls in pre-1980s UK housing stock reveals unexpected damp, non-compliant wiring, and structural issues far more often than not. A contingency isn't pessimism — it's professional practice.
Get Three Quotes Minimum
A wide spread in quotes (£8k, £14k, £18k for the same job) signals different scopes being priced. Go back to outliers with specific questions before assuming the cheapest is the best deal — cheap quotes that grow mid-project are far more expensive than honest ones that don't.
Further reading: The HomeOwners Alliance provides independent renovation guidance and contractor vetting advice. Visit HomeOwners Alliance for renovation guidance.
The Costs That Consistently Get Underestimated
Preparation costs — stripping wallpaper, repairing plaster, levelling floors before laying new materials — are frequently omitted from initial estimates because they are less visible than the finished result. Structural surprises are the other major category: discovering a damp course issue, a cracked lintel, or inadequate wiring during a renovation can double the budget of a straightforward job. Neither of these are freak occurrences. They are normal features of older UK housing stock and should be assumed rather than hoped against.
Building a Contingency Into Your Estimate
A 10–15% contingency is the minimum for any renovation project involving work to walls, floors, or ceilings. For older properties — typically pre-1980 construction — 20% is more appropriate. This is not pessimism. It is the result of running the numbers on completed projects across a large enough sample to see that surprises are statistical near-certainties in renovation work. The contingency is not an allowance for recklessness — it is a recognition that hidden problems exist in most buildings and will be discovered during work.
Labour Costs Are Usually the Largest Line Item
Tradespeople in the UK typically charge £150–£300 per day for general trades such as carpentry, plastering, and tiling, rising to £300–£500+ for specialist trades such as electricians and plumbers in higher-cost regions. Labour often represents 50–60% of total renovation costs on projects that require skilled tradespeople. If your initial estimate is based primarily on material costs, double it as a starting point and then get formal quotes to validate or refine the figure.
Getting Multiple Quotes and Reading Them Correctly
Three quotes is the practical minimum for any significant renovation job. But the key is making the quotes comparable — if one quote includes materials and another does not, or one specifies a premium specification and another uses budget materials, you are not comparing like with like. Ask each contractor to quote on the same specification. Any quote that is significantly lower than the others deserves scrutiny: ask specifically what is excluded, what materials are assumed, and whether the labour hours are realistic for the scope of work described.