Free Tool
Loft Conversion Cost Calculator
Velux, dormer, L-shaped, mansard — get an instant cost range for your loft conversion across London and the South East.
Estimate Your Loft Conversion Cost
Adjust the inputs below for an instant indicative range based on London & South East project data.
Box or flat-roofed dormer extension on rear slope. Adds significant usable floor space.
Good quality — mid-range materials, decent bathroom suite, solid finish
INDICATIVE COST RANGE — STANDARD
£50k – £72k
Dormer · Outer London
Cost Benchmark Comparison
Basic
£44k – £63k
Standard ✓
£50k – £72k
High Spec
£63k – £92k
Estimated Cost Breakdown — £61k midpoint
* Indicative split based on standard specification. Actual proportions vary by project.
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From £95 — based on your actual drawings and spec.
* Indicative ranges only. Actual costs depend on existing roof structure, building regulations requirements, party wall matters, structural conditions, and specification. Not a formal quotation.
Which Loft Conversion Type Is Right for Your Home?
Velux
£30k – £45k
Best for: Where roof pitch already provides headroom
Least disruptive. Usually permitted development.
Dormer
£45k – £65k
Best for: Most terraced and semi-detached homes
Most popular type. Good value for floor area gained.
L-shaped
£55k – £80k
Best for: Victorian and Edwardian terraces with rear return
Maximises floor area on properties with existing back additions.
Mansard
£75k – £100k
Best for: Where maximum floor area is required
Usually requires planning permission. Best for period properties.
Hip-to-gable
£40k – £60k
Best for: End-of-terrace and semi-detached homes
Extends one end to create more usable volume.
South East base costs shown. Inner London adds approx 20%, Outer London adds approx 10%.
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