Do I need planning permission for a loft conversion?

Many loft conversions fall under permitted development, but dormers facing a road, mansards, and homes in conservation areas usually need planning permission. Building control sign-off is always required.

Does a loft conversion add value?

A well-built loft conversion that adds a double bedroom and en-suite typically adds more to the property value than it costs, especially in higher-value areas, though that is never guaranteed.

Which loft conversion is cheapest?

A rooflight or Velux conversion is cheapest because it keeps the existing roof line. A dormer costs more but adds head height and floor space, which is why it is the most common choice.

Home / Cost guides / Loft conversion

How much does a loft conversion cost in the UK?

A loft conversion is one of the best-value ways to add a bedroom and often a bathroom without losing garden space. What you pay depends mostly on the roof type you choose.

From

£22,000

Typical

£45,000

Up to

£75,000

for the project · typical UK job, 2026

Time on site: 6 to 10 weeks on site for a typical dormer

Price your loft conversion

Adjust for your job and area to get a range.

What's included in the price

Structural work, new floor joists and staircase
Insulation, plastering, electrics and heating
Windows or dormer construction
Building control sign-off

What changes the cost

Roof type: a rooflight (Velux) conversion is cheapest, a dormer is the common choice, a mansard is the most expensive
Whether you add an en-suite bathroom
Head height and whether the roof needs raising
Finish level and staircase position

Costs by area

London and the South East run 15 to 30 percent above the national figures, mainly on labour.

Common questions

Do I need planning permission for a loft conversion?: Many loft conversions fall under permitted development, but dormers facing a road, mansards, and homes in conservation areas usually need planning permission. Building control sign-off is always required.
Does a loft conversion add value?: A well-built loft conversion that adds a double bedroom and en-suite typically adds more to the property value than it costs, especially in higher-value areas, though that is never guaranteed.
Which loft conversion is cheapest?: A rooflight or Velux conversion is cheapest because it keeps the existing roof line. A dormer costs more but adds head height and floor space, which is why it is the most common choice.

These are independent guide prices based on typical UK jobs in 2026. Your actual cost depends on your property, spec, access and where you live. Always get at least three written quotes before committing.