Cost Calculator
Loft conversion cost calculator
Find out roughly how much a loft conversion costs by type, floor area and ensuite. A ballpark to plan around, not a quote.
In short
Loft conversions in the UK typically cost from about £1,250 to £2,550 per square metre of new floor area, ex VAT, depending on type.
A simple rooflight conversion is the cheapest, then dormer, then hip to gable, with a full mansard the most expensive. Adding an ensuite adds roughly £4,000 to £7,000.
Enter your details for an indicative range. For a number you can build against, send us your drawings.
Your details
Usable floor area the conversion will create.
Indicative cost
Fill in your details to see an indicative cost range.
This is a rough guide. For a proper, measured estimate you can quote from or build against, send us your drawings.
Get a measured estimateHow this estimate is worked out
The calculator multiplies the new floor area by a cost per square metre band for the conversion type you choose. Rooflight conversions keep the existing roofline and are cheapest, dormers and hip to gable add structure and roof alteration, and a mansard rebuilds the whole roof so sits at the top.
If you choose an ensuite, the calculator adds a fixed allowance for the extra plumbing, waterproofing and fit out involved. That allowance is on top of the floor area figure.
Everything is ex VAT and covers the conversion build only. It excludes party wall costs, planning and design fees, and any structural surprises found once the floor is opened up.
What drives the cost
Conversion type and roof works
How much of the existing roof has to change is the single biggest driver. A rooflight job barely touches it, a mansard rebuilds it entirely.
Staircase and head height
Fitting a compliant staircase and achieving head height can mean structural changes below the loft, which adds cost that floor area alone does not capture.
Bathrooms and plumbing
Running soil and water up to a new ensuite, plus tiling and sanitaryware, adds a meaningful and variable chunk to the budget.
Structural steels and dormers
New floor joists, supporting steels and dormer construction vary with span and design, and need proper structural calculations.
An indicative ballpark only
These figures are a rough guide based on typical UK rates and are shown ex VAT. They are not a quote and should not be used to price or build a real job. Every project differs on specification, site conditions, access and local rates. For a figure you can actually quote from or build against, send us your drawings and we'll prepare a proper, measured estimate.
Frequently Asked Questions
Ready for a real number you can quote from?
A calculator gives you a ballpark. Send us your drawings and we'll come back with a professional, measured estimate, a fixed fee and a turnaround time.
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