Dormer Loft Conversion Cost UK 2026

A dormer loft conversion adds a vertical-walled extension out of the roof slope, dramatically increasing usable head height and floor area. In 2026, dormer conversions cost £38,000–£75,000 for a typical UK semi or terrace, with London 30–35 % higher.

Quick answer

Typical UK price range: £38,000–£85,000. Typical time: 7–9 weeks.

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Loft conversion calculator

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Loft conversion type Velux / rooflight Dormer Hip-to-gable Mansard L-shaped

Loft floor area (m²)

Region London South East South West Midlands North of England Scotland Wales Northern Ireland

Specification level Basic / standard Mid-range Premium / high-end

Extras

En-suite bathroom £8,000–£12,000 Extra Velux windows £1,500–£1,500 Underfloor heating £2,500–£4,500 New staircase £1,800–£3,500 Walk-in wardrobe £1,500–£3,500

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Budget Under £5,000 £5,000 – £15,000 £15,000 – £30,000 £30,000 – £60,000 £60,000+ Not sure

Timeline As soon as possible 1 – 3 months 3 – 6 months 6+ months Just researching

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Key points

• Adds 30–50 % more usable floor area than a Velux
• Permitted development for rear dormers on most UK homes
• Costs £1,500–£2,200 per m² — depending on dormer width
• Standard dormer takes 7–9 weeks on site

Cost breakdown

Item	Low	High
Dormer build (frame, weatherproofing)	£10,000	£18,000
Roof works + tiling	£3,500	£7,000
Insulation, plasterboard, plastering	£4,000	£7,500
Staircase + flooring	£3,500	£6,500
Electrics + heating	£2,500	£4,500
Architect + building control + party wall	£3,000	£5,500

Cost by UK region

Region	Typical cost
London	£83,025
South East	£76,875
South West	£67,650
Midlands	£61,500
North England	£55,350
Scotland	£58,425
Wales	£55,350

How to save money

• Specify a "box" dormer for the most internal head height
• Add Velux to the front pitch for extra light if rear dormer faces north
• Always serve party wall notices — costs £100–£300 to do correctly

How to find a trusted tradesperson

Get at least 3 quotes from vetted UK trade networks:

• Checkatrade
• MyBuilder
• Bark

FAQs

Do I need planning permission for a dormer?

Rear dormers are usually permitted development if under 40 m³ (terrace) or 50 m³ (semi/detached). Front dormers always need planning permission.

How big can a dormer be?

Up to 40 m³ added volume on a terrace, 50 m³ on a semi/detached. Width is typically 3–4 m for a single dormer; bigger dormers need engineer-sized steels.

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Disclaimer: Prices are guide ranges based on 2026 UK market data. Get quotes from local tradespeople for accurate pricing.