Renovation Budget & Contingency Guide (2026)

Key Takeaways

Always include a 10 to 15% contingency on top of the build cost.
Budget for professional fees (design, structural, surveys) at around 10 to 15% of build cost.
Remember VAT, building control fees, and party wall costs.
Hidden issues in older London homes are the main reason budgets blow.
A detailed, itemised quote keeps costs predictable.

A renovation that stays on budget starts with a budget that is realistic. The figure on the builder's quote is only part of the true cost. Here is how to budget properly and avoid the surprises that catch London homeowners out.

Start with the build cost

Get a detailed, itemised quote from your contractor that breaks down labour and materials by element. This is the most reliable basis for the build cost and lets you compare contractors like with like. Vague round-number quotes are where budgets unravel.

Then add the extras people forget

Professional fees: design, structural engineering and surveys, around 10 to 15% of build cost.
VAT: most renovation work is standard-rated at 20%, so confirm whether quotes include it.
Building control and planning fees.
Party wall surveyor fees if neighbours dissent.
Skips, scaffold and parking permits, which add up in London.
Temporary accommodation if you cannot live in during the works.

The contingency is not optional

Set aside a contingency of 10 to 15% of the build cost. In older London homes, opening up walls and floors routinely reveals old wiring, damp, rot or weak structure. The contingency is what lets you deal with these without stalling the project or compromising the finish. Treat it as insurance, not spare spending.

Keeping control

The budget-killers are scope creep, late decisions and hidden issues. Decide promptly, resist adding work mid-project unless you adjust the budget, and choose a contractor who flags issues early with clear costs. For an itemised quote you can rely on, contact us or call 07472 424 226.

The GS Renovation Team

GS Renovation & Home Improvements has delivered kitchen, bathroom, structural and extension projects across London for over 30 years. This guide reflects current UK industry pricing and our hands-on site experience.

Frequently Asked Questions

How much should I budget for a renovation?

Budget for the build cost plus professional fees of around 10 to 15% (design, structural engineering and surveys), VAT where applicable, building control and any party wall fees, and a contingency of 10 to 15%. An itemised quote from your contractor is the most reliable basis for the build cost itself.

What is a renovation contingency and how much should it be?

A contingency is a reserve fund for unexpected costs that emerge once work starts, such as hidden damp, old wiring or weak structure in older homes. Set it at 10 to 15% of the build cost. It is not optional spending, it is insurance that keeps the project moving without painful compromises.

What hidden costs do people forget?

Commonly forgotten costs include VAT (most renovation work is standard-rated at 20%), professional and structural fees, building control charges, party wall surveyor fees, skip and waste removal, scaffold and parking permits in London, and temporary accommodation if you move out.

Why do renovation budgets go over?

The main reasons are hidden problems uncovered in older properties, scope creep where the homeowner adds work mid-project, late decisions causing delays, and vague initial quotes that miss items. A detailed quote, a contingency and disciplined decisions keep the budget under control.

Is it cheaper to renovate all at once or in stages?

Renovating all at once is usually cheaper overall and faster, because trades work efficiently in sequence and you only strip out and set up once. Staging spreads the cost over time but increases the total and the disruption.

Renovation Budget & Contingency