Loft budget planner
Loft Conversion Cost Calculator UK
Get an indicative cost range for your loft conversion project. Choose the conversion type, size, specification and location for a UK market estimate.
Typical project budget
£20,000–£90,000+
Biggest cost drivers
Conversion type, stairs, en-suite, planning
Best use
Comparing loft options before design fees
Finished loft example
Useful for picturing the end result — but the structural route is what really drives the budget.
Loft cost snapshot
Dormer vs mansard is usually the biggest budget fork
Use the calculator to compare conversion routes, then check the loft types and cost-per-m² guides before you commit to plans.
Remember
Staircase design, steelwork and en-suite plumbing can change the economics more than cosmetic finishes do.
Good next step
Compare the loft route against an extension if you are choosing where to add space.
Estimated Loft Conversion Cost
Indicative range. Not a quote. Includes a 10% contingency.
Cost Breakdown
| Structural Works | — |
| Staircase | — |
| Plumbing & Electrical | — |
| Admin & Permissions | — |
| Contingency (10%) | — |
| Estimated Total | — |
How We Estimate
- • Estimates assume a standard UK semi-detached or terraced property. Flats and end-terrace properties may have different structural requirements.
- • Prices include design, structural engineer, building control and all trades.
- • Loft conversions typically require Building Regulations approval even under Permitted Development.
- • This is an indicative estimate, not a quote.
- • Last updated: Q2 2026.
Calculate More
Understand Your Loft Conversion Cost
Quick answers for UK homeowners
How much does a loft conversion cost in the UK?
Most UK loft conversions fall into a broad range depending on size, structure, access, dormers, bathrooms and finish level. Use the calculator as a planning estimate before getting fixed quotes.
What affects the cost most?
The biggest cost drivers are conversion type, roof structure, floor strengthening, staircase position, insulation, windows and whether you add a bathroom.
Is this a replacement for a builder quote?
No. It is a budgeting tool to help you understand likely ranges and compare options before speaking to builders or designers.
Related planning pages
Loft planning notes
What to check before treating a loft estimate as affordable
Loft conversion costs depend on the existing roof structure, head height, staircase position, dormer size, insulation, fire safety upgrades and whether you are adding an ensuite. A rooflight conversion can be relatively contained; a dormer or hip-to-gable conversion usually needs more structural work and a larger contingency.
Use the calculator to compare conversion types before commissioning detailed surveys. If the estimate is close to your budget ceiling, check whether an extension, internal reconfiguration or phased finish would be a better route.
Quote details that matter
- Confirm whether structural calculations and building control are included.
- Ask how staircase, fire doors, insulation and smoke alarms are handled.
- Check whether bathroom plumbing, roof windows and dormer finishes are included.
- Allow for decoration, flooring, storage and final electrics.
- Ask whether scaffolding, skips and parking permits are included.
This calculator follows the selected country
Use the location controls above. Every estimate uses only the selected country's currency, units and local cost assumptions. Browse calculators or review location coverage.