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Cost a loft conversion.
Velux, dormer, hip-to-gable, mansard — the 2026 trade-pricing reference for UK loft conversions.
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Costs, timelines, pitfalls and the right questions to ask before any loft conversions starts on loft Cost UK 2026 — Trade Pricing Reference.
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Top tips
Hiring a loft conversions, without the regret.
Four moves that separate a smooth job from a nightmare.
Cheap quote excludes en-suite
Adding later costs more. Specify in scope.
Architect not included
Some quotes exclude design. Confirm whether arch + structural engineer in price.
Below-market quotes
Specialist firms generally not cheapest. Quality matters for resale.
Costs & timeline
Know what it costs. Know when it ends.
Indicative UK ranges and a typical week-by-week schedule.
Cost range
By job type
Inc. VAT · 2026
Source: NMT quotes
Source: NMT quotes
Velux-only conversionSmallest type
£30k–£45k
Rear dormer conversionMost popular
£40k–£65k
Hip-to-gable conversionEnd-terrace
£50k–£80k
Hip-to-gable + dormerMax space
£60k–£110k
Mansard conversionPremium urban
£60k–£110k
L-shape dormer (Victorian)London common
£55k–£95k
!
Quote spread is typically ± 18% — always get 3 quotes.
Timeline
Dormer loft conversion · week by week
Typical
6 phases · 10 wk
6 phases · 10 wk
W1
W2
W3
W4
W5
W6
W7
W8
W9
W10
Structural + design
Strip + steels in
Dormer build + roof
1st + 2nd fix
Plaster + finishes
Snags + handover
!
Schedule slips on dependencies — pad each phase by 10–20% for real-world delays.
At a glance
Infographic · VideoThe Loft Conversions briefing.
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Loft Conversions quick-view
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Loft Conversions explained
UK loft conversion prices vary by type, location, and complexity. This reference helps spot fair quotes. All prices include VAT and quality finishes for 2026.
What Does the Work Involve?
Pricing reference — see individual guides for full process. London/SE 15-25% above national average. Conservation areas premium. Old buildings (Victorian) more complex than modern.
Typical Costs
| Item | Low (£) | High (£) | Notes |
|---|---|---|---|
| Velux-only conversion | 30,000 | 45,000 | Smallest type |
| Rear dormer conversion | 40,000 | 65,000 | Most popular |
| Hip-to-gable conversion | 50,000 | 80,000 | End-terrace |
| Hip-to-gable + dormer | 60,000 | 110,000 | Max space |
| Mansard conversion | 60,000 | 110,000 | Premium urban |
| L-shape dormer (Victorian) | 55,000 | 95,000 | London common |
| En-suite addition | 4,500 | 12,000 | Plus plumbing |
| Loft conversion stairs | 2,500 | 6,500 | Part K compliant |
| Velux roof window (per window) | 800 | 2,000 | Fitted |
| Loft insulation top-up | 300 | 1,500 | To 250mm |
| Loft boarding (Loft Leg system) | 500 | 2,000 | Storage |
| Architect/structural design | 2,500 | 10,000 | 10% of build |
How Long Does It Take?
Velux-only: 6-10 weeks. Dormer: 10-16 weeks. Mansard: 12-20 weeks. Total project: 4-8 months including design and approvals.
DIY or Professional?
Professional only. Building Regs notification mandatory.
Choosing the Right Tradesperson
Specialist loft conversion company or experienced builder. FMB or NFB member. 10-year warranty typical.
UK Regulations
Building Regs Part A, B, K, L, F, P. Planning permission for some. Lawful Development Certificate for permitted development. Listed buildings need consent.
Common Problems With Quotes
- Cheap quote excludes en-suite: Adding later costs more. Specify in scope.
- Architect not included: Some quotes exclude design. Confirm whether arch + structural engineer in price.
- VAT excluded: Always confirm.
- Below-market quotes: Specialist firms generally not cheapest. Quality matters for resale.
Frequently Asked Questions
How much should loft conversion cost in 2026?
Velux: £30,000-£45,000. Dormer: £40,000-£65,000. Mansard: £60,000-£110,000.
Why do quotes vary so much?
Specification, finish quality, brand, architect inclusion, party wall, regional rates. London 15-25% above national.
What payment structure?
25% deposit, staged payments. Avoid 50%+ deposits. Some specialists offer 0% finance.
Best ROI option?
Mid-range dormer with en-suite. £40,000-£60,000 spend, £60,000-£130,000 value uplift.
How long should warranty be?
10 years on workmanship. Manufacturer warranty on materials (windows, insulation).
Will it add planning issues?
Mostly no for permitted development. Conservation areas and listed buildings need consent. Front-facing dormer often needs permission.
This guide was written with AI assistance and is intended for general information only. Prices are estimates based on UK averages and may vary by region. Always get at least three quotes and consult a qualified professional before starting any work.
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