Property renovations almost always cost more and take longer than expected. The solution is not better luck — it is building the right buffers into your budget from the start. Here is a practical framework for estimating renovation costs and protecting yourself from overruns.
Use the Renovation Budget Calculator to build a room-by-room budget with contingency and value-add estimates.
Why Renovation Budgets Go Wrong
The most common reasons renovations exceed budget:
- Underestimating scope — "a light refurb" discovers structural issues, damp, or outdated wiring
- No contingency — treating the budget as exact rather than as a floor
- Competitive quotes — choosing the cheapest contractor who wins by underquoting
- Hidden costs — skip hire, planning fees, building control, structural calculations
- Specification creep — upgrading finishes or adding extras mid-project
A renovation budget has three layers: the baseline estimate, a contingency buffer, and a scope buffer for decisions made during the work.
Room-by-Room Cost Guide (UK, 2026)
These are approximate costs for a UK refurbishment including labour and materials at mid-market specification.
Kitchen
| Scope | Approximate cost |
|---|---|
| Basic refit (new units, worktops) | £5,000–£12,000 |
| Mid-range refit with new appliances | £12,000–£25,000 |
| Full remodel with structural changes | £25,000–£60,000+ |
Bathroom
| Scope | Approximate cost |
|---|---|
| Basic suite replacement | £3,000–£6,000 |
| Full refurb with new tiles | £5,000–£12,000 |
| High-spec with structural changes | £12,000–£25,000 |
Loft Conversion
| Type | Approximate cost |
|---|---|
| Velux (no structural change) | £20,000–£35,000 |
| Dormer conversion | £35,000–£55,000 |
| Hip-to-gable | £40,000–£65,000 |
| Mansard | £55,000–£85,000 |
Extension
| Type | Approximate cost |
|---|---|
| Single storey rear | £30,000–£60,000 |
| Double storey | £50,000–£100,000+ |
| Side return (London terrace) | £25,000–£50,000 |
Other Common Items
| Item | Approximate cost |
|---|---|
| Full rewire (3-bed house) | £6,000–£12,000 |
| New central heating system | £4,000–£8,000 |
| New roof (3-bed house) | £8,000–£18,000 |
| Damp-proof course | £800–£2,500 |
| Windows (whole house, double glazed) | £8,000–£20,000 |
| Interior decoration (whole house) | £3,000–£8,000 |
Costs vary significantly by region. London typically runs 20–40% above these figures.
The Contingency Rule
Always build in 15–20% contingency on any renovation budget.
For a renovation with a £40,000 scope:
- 15% contingency: £6,000 (more predictable work with good surveys)
- 20% contingency: £8,000 (older properties, structural unknowns)
For extensive refurbishments or conversions: 20–25% is safer.
The contingency is not free spending money — it is a buffer for the unexpected things you will find once walls are opened. Most experienced renovators use most or all of their contingency on significant projects.
Does the Renovation Add Value?
Not all renovations deliver a positive ROI. Value-add potential varies by renovation type:
| Renovation | Typical value added vs cost |
|---|---|
| Loft conversion (bedroom + bathroom) | 120–180% of cost |
| Extension | 100–150% of cost |
| Kitchen refit | 80–120% of cost |
| Bathroom refit | 70–100% of cost |
| New windows | 50–80% of cost |
| Decoration | 100–200% (low cost) |
| New boiler/heating | 60–80% of cost |
Returns depend heavily on:
- The value ceiling in your street (if neighbouring houses cap at £400k, a £50k renovation won't add £50k)
- Local buyer preferences
- The current state of the property (a run-down property gains more from basics than an already-good one gains from luxury upgrades)
Renovation vs Buying Finished
For buy-to-let investors, a key question is whether to buy a property needing work (and renovate it) or pay a premium for one already in good condition.
The calculation: if you can buy for £50,000 under market value and renovate for £25,000, you have made £25,000 in equity immediately. But the uncertainty, time, and stress of a renovation needs to be factored in.
Use the Renovation Budget Calculator to model your room-by-room scope, apply the right contingency, and assess the value-add potential before committing to a project.