2026 Pricing Guide
Loft Conversion Costs UK 2026
Velux, dormer, hip-to-gable or mansard — see what UK loft conversions really cost and get an instant estimate.
A loft conversion is one of the most cost-effective ways to add space and value, typically adding 10–20% to your home's value. In 2026, UK loft conversion costs range from £25,000 for a basic Velux conversion up to £70,000+ for a mansard with en-suite. The type of conversion, roof structure, headroom and whether you add stairs or a bathroom all drive the final price.
Loft Conversion Prices
How Much Does Each Loft Conversion Option Cost?
Prices below are indicative 2026 UK market rates and include labour and materials. Use our calculator for a personalised estimate.
Velux / Rooflight Conversion
£25,000 – £35,000
Lowest cost. Windows fitted into existing roof slope. Needs adequate headroom already.
Dormer Conversion
£35,000 – £50,000
Most popular. Box extension from the roof slope adds full headroom and floor space.
Hip-to-Gable Conversion
£40,000 – £55,000
Extends the hipped roof into a gable, ideal for semi-detached homes with side hip.
Mansard Conversion
£45,000 – £70,000
Alters the whole roof slope to a near-flat 72° pitch. Maximum space, highest cost.
En-Suite Bathroom (add-on)
£4,000 – £7,000
Compact shower room with WC and basin. Needs plumbing and waste runs from the loft.
Staircase & Structural Steel
£3,000 – £8,000
New fixed staircase (building regs required) and structural steelwork for opening.
* All prices are estimates. A site survey is required for an accurate quote. Use our calculator for a personalised estimate.
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The Loft Conversion Process Step by Step
Feasibility & Design
Surveyor checks headroom, roof structure and access. Architect draws plans and confirms permitted development vs. planning.
Permissions & Party Wall
Submit planning if needed (8 weeks). Serve party wall notices if you share a wall. Apply for building regulations.
Build (External)
Scaffolding, roof opened, dormer/steel installed, windows fitted, roof re-tiled. Most disruption is external.
Internal Fit-Out
Insulation, plasterboarding, first-fix plumbing and electrics, staircase installed, plastering.
Finish & Sign-Off
Second fix, decoration, flooring. Building inspector signs off and issues completion certificate.
Common Mistakes
4 Mistakes to Avoid
Not Checking Headroom First
If you have less than 2.2m headroom, a basic Velux won't work. Check before falling in love with the cheapest option — you may need a more expensive dormer.
Forgetting Building Regulations
All loft conversions need building regulations approval for structure, fire safety, insulation, stairs and electrics. Don't use a builder who skips this — you can't sell the house without completion certificates.
Underbudgeting for Stairs
A compliant fixed staircase (not a pull-down ladder) costs £3,000–£8,000 and eats floor space below. Plan where it goes early — it's non-negotiable for habitable use.
Ignoring Fire Safety
Building regs require fire doors, mains-wired smoke alarms and a protected escape route. Budget for replacing bedroom doors with fire doors and updating the smoke alarm system.
FAQs
Loft Conversion Cost FAQs
How much does a loft conversion cost in the UK in 2026?
A UK loft conversion costs £25,000–£70,000+ in 2026. A Velux conversion costs £25,000–£35,000, a dormer £35,000–£50,000, a hip-to-gable £40,000–£55,000 and a mansard £45,000–£70,000. Adding an en-suite costs £4,000–£7,000 extra.
Do I need planning permission for a loft conversion?
Most loft conversions fall under Permitted Development if they don't extend beyond the roof slope, aren't higher than the existing roof, use matching materials, and aren't in a conservation area. Dormers that face the highway usually need planning permission. Mansards almost always need planning permission.
How long does a loft conversion take?
A Velux conversion takes 4–6 weeks. A dormer takes 6–8 weeks. A mansard or complex conversion takes 8–12 weeks. Most work is done externally until the staircase goes in, keeping disruption low.
Will a loft conversion add value?
Yes — typically 10–20%, often more than the cost of the work. Adding a bedroom and bathroom to a 3-bed to make a 4-bed can add £40,000–£80,000 in value depending on location.
What headroom do I need for a loft conversion?
You need at least 2.2m of standing headroom at the centre of the loft after the new floor and insulation are added. If you don't have it, a dormer or mansard can create it, at higher cost. Raising the roof is possible but expensive.
Can I live in the house during the conversion?
Yes, in most cases. Scaffolding goes up outside and work happens through the roof until the staircase is installed near the end. Expect noise, dust and some disruption for 4–10 weeks. Many people move out for the final 1–2 weeks.
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