Home & Construction📅 8 April 2025⏱ 6 min read
How to Budget a Home Renovation: A Cost-per-Square-Metre Guide
Renovation costs are notoriously unpredictable — but not unknowable. Here is a room-by-room cost guide, the formula for contingency budgeting, and the hidden costs that wreck most budgets.
JW
James WhitfieldPersonal Finance & Maths WriterJames has written about personal finance, health metrics, and everyday mathematics for over six years. He holds a BSc in Mathematics from the University of Leeds.
Home renovation costs depend on specification, location, and the state of the existing structure. The cost-per-square-metre benchmarks below are for mid-range UK work (2024 prices) — premium finishes or structural complications will push these up significantly.
Room-by-Room Cost Benchmarks (UK, 2024)
Renovation TypeBudgetMid-rangePremium
Kitchen (per m2 floor)£800-1,200£1,500-2,500£3,500+
Bathroom (per m2)£600-900£1,000-1,800£2,500+
Loft conversion (per m2)£1,200-1,500£1,500-2,000£2,500+
Extension (per m2 GIA)£1,500-2,000£2,000-3,000£3,500+
Rewire (per m2)£25-35£35-50£50-70
Replumb (per m2)£30-45£45-65£65-90
Budgeting Formula with Contingency
Base cost estimate = Sum of all room/scope estimates
Contingency allowance:
New build or well-understood scope: 10-15%
Renovation of known-condition property: 15-20%
Victorian / Edwardian property (unknown structure): 20-30%
Listed building or complex works: 30-50%
Total project budget = Base estimate x (1 + Contingency %)
Example: kitchen renovation, 12 m2, mid-range spec:
Base estimate: 12 x £2,000 = £24,000
Contingency (20%): £4,800
Total budget: £28,800
Rule: never present a renovation budget without contingency.
The contingency is not waste — it is the most realistic part of the estimate.
The Hidden Costs That Wreck Budgets
Costs frequently excluded from initial quotes:
Planning permission (if required): £206-£462 application fee
Architect / designer fees: 5-15% of build cost
Structural engineer report: £400-£800
Party wall surveyor (shared walls): £700-£1,500 per owner
Building control fees: £400-£1,500 depending on works
Temporary accommodation: £0-£3,000+ per month
Skip hire: £200-£400 per skip
Site clearance before work starts: £300-£800
VAT: most building work is standard-rated at 20%
(New builds and some conversions are zero-rated — check with builder)
Adding VAT example:
Quote of £20,000 + VAT = £24,000 actual cost
Always ask: "Is your quote inclusive or exclusive of VAT?"
Value Added by Renovation Type
Rough UK average added value (varies enormously by location):
Kitchen renovation: recoups 50-75% of cost in sale price
Bathroom renovation: recoups 50-65% of cost
Loft conversion (adds bedroom): recoups 75-100% of cost
Extension (adds m2): recoups 70-90% of cost
These are averages — in strong markets, returns can exceed cost.
In weak markets or with poor specification, returns can be negative.
Return on investment formula:
ROI = (Sale price increase - Renovation cost) / Renovation cost x 100
Loft conversion costs £35,000, adds £45,000 to value:
ROI = (45,000 - 35,000) / 35,000 x 100 = 28.6%