Loft Conversion Costs London: Complete 2026 Price Guide

Loft conversions offer one of the best returns on investment for London homeowners, typically adding 20% to property value. This detailed cost guide breaks down every expense you can expect in 2026.

Average Loft Conversion Costs in London

London loft conversion costs significantly exceed the national average due to higher labor costs, stringent building regulations, and limited access in terraced properties.

Cost by Loft Type

• Velux/Roof Light: £35,000 – £50,000
• Dormer: £45,000 – £65,000
• Hip-to-Gable: £50,000 – £70,000
• Mansard: £60,000 – £85,000

Detailed Cost Breakdown

Structural Work (40-50% of budget)

• Roof alterations: £15,000-£25,000
• Steel beams installation: £3,000-£6,000
• Floor reinforcement: £4,000-£7,000
• Stairs: £3,000-£8,000 (depending on type)

Windows & Doors (10-15%)

• Velux windows: £800-£1,500 each
• Dormer windows: £2,000-£4,000
• Roof lanterns: £3,000-£8,000

Bathroom (if included) (15-20%)

• Basic bathroom suite: £3,000-£5,000
• Mid-range ensuite: £6,000-£10,000
• Luxury ensuite: £12,000-£20,000

Other Essentials

• Insulation (crucial for building regs): £2,000-£4,000
• Plastering: £2,500-£4,000
• Electrics: £2,000-£3,500
• Heating/radiators: £1,500-£2,500
• Decoration: £2,000-£4,000
• Flooring: £1,500-£3,000

Cost-Saving Strategies

While you should never compromise on structural integrity, there are legitimate ways to reduce costs:

1. Choose a Velux Conversion

The most affordable option, utilizing existing roof slopes with minimal structural changes. Perfect if you have adequate head height already.

2. Delay Interior Finishes

Get the structure weathertight first, then complete decoration yourself or in stages.

3. Standard Fixtures

Designer bathrooms and kitchens add 30-40% to costs. Mid-range options look excellent and last just as long.

4. Off-Peak Timing

Builders are typically quieter October-February. You may secure better rates outside summer months.

Hidden Costs to Budget For

• Party Wall Agreements: £700-£1,200 per wall
• Structural Engineer: £500-£1,500
• Building Control: £800-£1,500
• Architect/Designer: £2,000-£8,000
• Planning Fees: £206 (if required)
• Scaffolding: £1,500-£3,000
• Skip Hire: £300-£600
• Temporary Accommodation: Variable (if house uninhabitable)

Return on Investment

In desirable London postcodes, a loft conversion typically adds:

• 1-bedroom conversion: +15-18% property value
• 2-bedroom conversion: +18-22% property value
• Master suite with ensuite: +20-25% property value

For a £600,000 property, even a modest 15% increase equals £90,000—well above the £45,000-65,000 typical spend.

Getting Accurate Quotes

Always obtain at least 3 detailed quotes. Each should itemize:

• All structural work
• Materials specifications
• Labor costs
• Project timeline
• Payment schedule
• What’s NOT included

Be wary of quotes that are 30%+ below others—this often indicates:

• Inexperience with loft conversions
• Missing essential work
• Use of substandard materials
• Unlicensed contractors