How Much Does a Loft Conversion Cost? (2026 UK Guide)

Loft Conversion Costs at a Glance (2026)

Conversion Type	Typical Cost	Best For
Velux (roof light) conversion	£15,000–£25,000	Rooms with enough headroom, no planning needed
Dormer conversion	£25,000–£45,000	Adds headroom and floor space, most popular type
Hip-to-gable conversion	£30,000–£50,000	Semi-detached or detached with hipped roof
Mansard conversion	£40,000–£65,000	Maximum space, usually needs planning permission
L-shaped dormer	£40,000–£65,000	Victorian terraces, creates large master suite

Prices include all structural work, insulation, staircase, electrics, plumbing for an en-suite, and basic finishing. Furniture and decoration are extra.

What's Included in a Loft Conversion Quote?

A full loft conversion quote from a reputable contractor should include:

• Structural design and engineer's drawings
• Steel beam installation (if required)
• Floor structure (new joists at correct spec)
• Dormer structure and roof covering (if applicable)
• Insulation (floor, walls, and roof)
• Windows and Velux rooflights
• New staircase (included in most full packages)
• First and second fix carpentry
• Plasterboard and skim plaster
• Electrics (lighting, sockets, smoke detector)
• En-suite plumbing (if included in scope)
• Building Regulations compliance throughout

What's not included in most quotes: flooring, decoration, furniture, kitchen/bathroom fittings for the en-suite, and architect fees if you manage them separately.

Do I Need Planning Permission?

Most loft conversions fall under Permitted Development (PD) rights and don't need planning permission, as long as:

• The volume addition is under 40m³ (terraced) or 50m³ (semi/detached)
• No extension is higher than the existing roof ridge
• Materials match the existing house
• No side-facing windows at lower storey level overlooking a neighbour

You will need planning permission for: mansard conversions, properties in conservation areas or Article 4 zones, listed buildings, and anything that alters the roofline beyond PD limits.

All loft conversions require Building Regulations approval regardless — this covers structural safety, fire escape, and insulation. Budget £500–£800 for Building Control fees.

What Affects the Cost?

• Staircase position — fitting a new staircase into a tight landing can require structural alterations to the existing floor. This is often where costs escalate unexpectedly
• En-suite — adding a bathroom to the loft adds £3,000–£7,000 to the project cost
• Head height — if your existing loft doesn't have 2.2m clear height at the ridge, a Velux conversion won't work without a structural raise, pushing you to a dormer
• Access to the property — scaffolding for a terrace mid-row costs more than a detached property with drive access
• Structural complexity — older properties with undersized or complex roof structures cost more to engineer
• Location — London and South East conversions run 25–40% above national average

How Long Does a Loft Conversion Take?

Conversion Type	Typical Duration
Velux conversion	4–6 weeks
Single dormer	6–10 weeks
Hip-to-gable or L-shaped	8–12 weeks
Mansard	10–16 weeks

Add 4–8 weeks before start for planning/Building Regulations submissions and structural drawings. Total project time from first call to usable room: 4–6 months is realistic for a dormer.

Is a Loft Conversion Worth It?

In most UK housing markets, yes. Typical return figures:

• Adding a bedroom increases value by 10–15% in most UK locations
• Adding a bedroom with en-suite increases value by 15–20%
• On a £350,000 home, a 15% uplift = £52,500 added value for a £30,000 conversion — roughly 1.7x return

Caveats: return depends on the local market, the quality of the finish, and whether nearby comparable properties have loft rooms. Don't over-capitalise on a street where everyone has 3-bed semis and yours would become a 5-bed.

Frequently Asked Questions