L-Shaped Loft Conversion Cost UK 2026

An L-shaped loft uses the main roof plus the rear-extension or back addition roof to create an L-shaped floor plan. Very popular in London Victorian terraces, costing £55,000–£90,000 in 2026.

Quick answer

Typical UK price range: £55,000–£95,000. Typical time: 9–11 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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Estimate only. Prices reflect 2026 UK market data — get quotes from local tradespeople for accurate pricing.

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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

• Usually two dormers — one rear, one over the back addition
• Adds enough space for a master bedroom + en-suite + study/dressing room
• £2,200–£3,000 per m² — premium because of two dormer builds
• Permitted development in many cases (subject to 40/50 m³ rule)

Cost breakdown

Item	Low	High
Main rear dormer	£10,000	£18,000
Back-addition dormer	£8,000	£15,000
Roof + waterproofing	£5,000	£9,000
Internal finishing	£8,000	£14,000
Staircase + flooring	£4,000	£7,000

Cost by UK region

Region	Typical cost
London	£101,250
South East	£93,750
South West	£82,500
Midlands	£75,000
North England	£67,500
Scotland	£71,250
Wales	£67,500

How to save money

• Get the architect to maximise the back-addition dormer — easy extra space
• Order all glazing at once — bulk pricing
• Consider Velux on the front pitch — keeps the streetside look unchanged

How to find a trusted tradesperson

Get at least 3 quotes from vetted UK trade networks:

• Checkatrade
• MyBuilder
• Bark

FAQs

Can my house have an L-shaped loft?

Only if you have a “back addition” (rear closet wing common in Victorian terraces). Modern semis usually can’t do L-shaped.

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