Instant
01 · Ask
Rooflight, dormer or mansard?
Roof shape and headroom dictate options. Describe the loft and the AI tells you which conversion type fits.
Compare loft vs extension.
Loft conversion or extension? — cost, value, planning and disruption compared for UK homes.
✓ Updated May 2026✓ Free quotes✓ Vetted pros
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Hire a loft conversion specialist. Headroom checked, steels designed.
Read the brief on headroom, fire doors and Party Wall — then let Three local loft specialists quote.
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02 · Read the brief
Walk in informed
Building Regs Part B/K, Party Wall Awards, structural calcs, planning vs permitted development. Know the rules.
60 seconds
03 · Compare
Compare 3 specialist quotes
Three local specialists quote on the same drawing — structural, fit-out, en suite — so you compare like-for-like.
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Top tips
Hiring a loft conversions, without the regret.
Four moves that separate a smooth job from a nightmare.
Headroom is the deal-breaker.
Building Regs need 2.0m clear above stairs and over 50% of floor area. Survey headroom first — anything less and you're in dormer or roof-lift territory.
Fire-rated doors throughout the route.
Loft conversions need 30-minute fire-rated doors on every room off the stair from the ground floor up. Cheap doors fail Building Control.
Get a structural engineer.
Steel beams or padstones on existing walls need calcs. Pay £400–£800 for an SE — saves £5,000 in retrofit reinforcement.
Party wall agreement if attached.
Terraced or semi-detached needs a Party Wall Award before steel goes in. Skip this and your neighbour can stop the job.
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
Rooflight only conversion (Velux)
£25k–£45k
Dormer loft conversionInc. en suite
£45k–£80k
Hip-to-gable conversion
£50k–£85k
Mansard conversion
£60k–£110k
Loft stair install only
£1.5k–£4.5k
Structural engineer fees
£400–£1.5k
!
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.
Infographic
Loft Conversions quick-view
Video guide
Loft Conversions explained
Loft conversion vs single-storey extension — both add space, different impacts. Compare costs, value uplift, and ROI. Expect different value-add per pound spent.
What Does the Work Involve?
Loft: uses existing roof space. No garden lost. Adds extra storey. Single-storey extension: adds new structure outward. Uses garden space. Same level as existing. Both add living space, different impacts on home.
Typical Comparisons
| Aspect | Loft Conversion | Extension |
|---|---|---|
| Typical cost | £30,000-£80,000 | £35,000-£80,000 |
| Floor space added | 25-50m² | 15-40m² |
| Value uplift | 15-25% | 10-20% |
| ROI | 100-200% | 70-120% |
| Garden impact | None | Loses garden space |
| Disruption | Moderate (loft access) | Major (extension footprint) |
| Planning permission | Often permitted dev | Often required |
| Build time | 10-16 weeks | 12-20 weeks |
How Long Does It Take?
Loft conversion: 10-16 weeks. Single-storey extension: 12-20 weeks. Both projects 4-8 months total.
DIY or Professional?
Both require professional specialists. Building Regs notification mandatory for both.
Choosing the Right Tradesperson
Loft conversion specialist for first. General builder for extension. Architect for both.
UK Regulations
Both require Building Regs. Loft often permitted development. Extension may need planning permission depending on size and conservation status.
Common Decision Factors
- Garden lost: Extension loses garden space. Loft doesn't. Garden important?
- Headroom limitation: Loft headroom 2.2m+ required. Some lofts don't qualify.
- Stair location: Loft needs new staircase, often eats existing room. Extension uses existing access.
- Value uplift per cost: Loft typically better ROI (100-200% vs 70-120%).
Frequently Asked Questions
Loft or extension — which better?
Loft for better ROI and garden preservation. Extension for level access (same floor) and where loft headroom inadequate.
Cost per m² compared?
Loft: £1,200-£2,000 per m². Extension: £1,500-£3,500 per m². Loft typically cheaper per m².
Value uplift compared?
Loft: 15-25% property value. Extension: 10-20%. Loft typically wins per cost.
Garden preservation?
Loft: 100% preserved. Extension: 15-40m² lost. Important for family or gardening homes.
Headroom constraint?
Loft needs 2.2m+ over 50% of usable area. Extension no headroom concern.
Both possible?
Yes — combined loft conversion + extension. £80,000-£150,000+. Maximum space addition.
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.
NEWAI Trade Assistant
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