A loft conversion is one of the smartest ways to add space and value to a UK home — often adding 20-25% to your property's value without the hassle of moving. But costs vary enormously depending on the type of conversion you choose.

This guide covers everything: costs by conversion type, labour breakdown, what's included, planning permission rules, build timelines, and a full sample quote so you know exactly what to expect in 2026.

Loft Conversion Cost at a Glance — UK 2026

Conversion Type Cost Range Best For
Velux (rooflight) £15,000-£25,000 Budget option, no external changes, quick build
Rear dormer £25,000-£50,000 Most popular, adds full headroom, usually permitted development
Hip-to-gable £40,000-£65,000 Semi-detached/detached homes with hipped roofs
Mansard £45,000-£75,000 Maximum space, flat roof rear wall, usually needs planning
Hip-to-gable + rear dormer £50,000-£75,000 Maximum space on semi-detached homes

Key Insight: The conversion type is driven by your roof shape, not your budget. A terraced house with a ridge roof suits a rear dormer. A semi-detached with a hipped roof needs a hip-to-gable. Your builder or architect will tell you which type works for your property.

Loft Conversion Types Explained

Velux / Rooflight Conversion (£15,000-£25,000)

The simplest and cheapest option. No changes to the roof structure — just Velux windows fitted into the existing roof slope, plus a staircase, floor strengthening, insulation, and electrics.

  • Pros: Cheapest, fastest (4-5 weeks), no planning permission needed
  • Cons: Limited headroom (depends on roof pitch), less usable space, no additional floor area
  • Best for: Homes with a roof pitch of 35°+ and sufficient ridge height (2.2m+)

Rear Dormer Conversion (£25,000-£50,000)

The most popular type in the UK. A box-shaped extension is built out from the rear roof slope, creating a room with full standing headroom and vertical walls.

  • Pros: Full headroom, large usable space, usually permitted development
  • Cons: Changes the look of the rear of the house, more expensive than Velux
  • Best for: Terraced and semi-detached homes, most roof types

Hip-to-Gable Conversion (£40,000-£65,000)

The sloping side wall (hip) is rebuilt as a vertical wall (gable), creating significantly more floor space. Often combined with a rear dormer for maximum room.

  • Pros: Transforms unusable hip space into full-height room
  • Cons: More structural work, higher cost, may need planning in some areas
  • Best for: Semi-detached and detached homes with hipped roofs

Mansard Conversion (£45,000-£75,000)

The rear roof slope is rebuilt at a near-vertical angle (72°), with a flat roof on top. This creates the maximum possible space but involves the most structural work.

  • Pros: Maximum space, almost like a full storey extension
  • Cons: Most expensive, almost always needs planning permission, longest build time
  • Best for: Properties where maximum space is the priority, Victorian/Edwardian terraces in London

What's Included in the Cost?

A loft conversion price should include all of the following:

Item Typical Cost
Structural steelwork (RSJs) £1,500-£3,500
Floor strengthening £1,000-£2,500
Staircase (supply & fit) £2,000-£5,000
Velux windows (x2) £1,200-£3,000
Dormer construction £5,000-£15,000
Insulation (100mm+ rigid board) £1,500-£3,000
Plasterboarding & plastering £2,000-£4,000
Electrics (lights, sockets, smoke alarms) £1,500-£3,000
Plumbing (radiators / underfloor heating) £800-£2,000
Fire door & fire safety measures £800-£1,500
Painting & decorating £800-£1,500
Flooring £500-£1,500
Building regulations application £400-£800
Architectural drawings £1,000-£2,500
Structural engineer calculations £400-£800

En-Suite Bathroom — Additional Cost

Most loft conversions include an en-suite. This adds:

En-Suite Level Additional Cost What You Get
Basic shower room £3,000-£5,000 Shower enclosure, toilet, basin, basic tiles
Mid-range en-suite £5,000-£8,000 Walk-in shower, wall-hung toilet, vanity unit, porcelain tiles
High-end en-suite £8,000-£12,000 Large walk-in shower, underfloor heating, designer fittings, large format tiles

For a full bathroom cost breakdown, see our new bathroom cost UK guide.

Pro Tip (for builders): Always quote the en-suite as a separate line item. Some clients want to defer the en-suite to save money upfront, and a clear breakdown gives them that flexibility. Use an itemised quote to show exactly what's included. See our guide on how to quote a loft conversion.

Regional Price Differences — UK 2026

Region Rear Dormer Cost vs National Average
London £40,000-£65,000 +30-50%
South East £30,000-£50,000 +10-20%
Midlands £25,000-£45,000 Average
North West £22,000-£40,000 -5-15%
North East £20,000-£38,000 -10-20%
Scotland £22,000-£42,000 -5-15%
Wales £20,000-£38,000 -10-20%

London loft conversions are significantly more expensive due to higher labour costs, parking restrictions, skip permit fees, and the prevalence of mansard conversions (which are more complex).

Planning Permission & Building Regulations

These are two separate things — and understanding the difference is critical:

Planning Permission

Most loft conversions fall under Permitted Development (no planning permission needed), provided:

  • Additional volume doesn't exceed 40 m³ (terraced) or 50 m³ (detached/semi)
  • Materials match the existing house
  • No extension beyond the existing roof plane facing a highway
  • The highest point doesn't exceed the existing roof ridge
  • No balconies or raised platforms (Juliet balconies are usually fine)

You WILL need planning permission for: mansard conversions, properties in conservation areas, listed buildings, flats, and any conversion that exceeds PD limits.

Building Regulations

ALL loft conversions need building regulations approval — this is non-negotiable. Building control will inspect:

  • Structural integrity (floor joists, steelwork, load paths)
  • Fire safety (fire doors, smoke alarms, escape windows, protected stairwell)
  • Insulation (must meet current Part L standards)
  • Staircase (headroom, pitch, width, handrails)
  • Electrics (Part P certification)

Building regs application costs £400-£800. Your builder should handle this, but always check it's included in the quote.

Sample Quote — Rear Dormer Loft Conversion

Here's a typical itemised quote for a rear dormer conversion on a 3-bed semi in the Midlands, creating a double bedroom with en-suite:

Item Cost
Architectural drawings & structural calculations £1,800
Building regulations application £500
Scaffolding (6 weeks hire) £1,200
Dormer construction (flat roof, timber frame, lead/GRP finish) £8,500
Structural steelwork (RSJs x2) £2,400
Floor strengthening (new joists, noggins) £1,800
Staircase (supply & fit, softwood, carpet-grade) £3,200
Velux windows x2 (centre pivot, 780x1180mm) £1,600
Dormer window (double glazed, UPVC) £900
Insulation (100mm Celotex between & under rafters) £2,200
Plasterboarding & skim (walls & ceiling) £2,800
Electrics — 8 downlights, 6 sockets, USB, smoke alarms £2,200
Plumbing — 2 radiators, en-suite connections £1,400
En-suite (shower, toilet, basin, tiling, fittings) £4,500
Fire doors x3 (FD30, fitted with intumescent strips) £900
Painting & decorating (walls, ceiling, woodwork) £1,200
Flooring (engineered oak, 18 m²) £1,100
Skip hire & waste removal £600
Total £38,800

That's a quality rear dormer with en-suite for under £40,000 in the Midlands. In London, expect £50,000-£65,000 for the same specification.

For Builders: Loft conversions are high-value jobs where a detailed, professional quote makes or breaks the sale. Homeowners compare 3-4 quotes — the one with clear line items and a professional layout wins trust. Try a quoting app to create itemised loft conversion quotes in minutes.

Build Timeline by Conversion Type

Conversion Type Build Time Pre-Build Planning
Velux (rooflight) 4-5 weeks 4-6 weeks
Rear dormer 5-7 weeks 4-8 weeks
Hip-to-gable 6-8 weeks 6-8 weeks
Mansard 7-10 weeks 8-12 weeks (planning permission)

Total time from first call to moving in: typically 3-5 months including design, approvals, and construction.

Does a Loft Conversion Add Value?

A loft conversion is consistently one of the highest-ROI home improvements in the UK:

  • A loft conversion typically adds 20-25% to your property's value
  • On a £300,000 home, that's £60,000-£75,000 of added value for a £30,000-£45,000 investment
  • Adding an extra bedroom + en-suite is particularly valuable — turning a 3-bed into a 4-bed moves you into a higher price bracket
  • Loft conversions add more value per pound spent than ground floor extensions in most cases
  • A building regulations completion certificate is essential — without it, buyers' solicitors will flag it and it could delay or reduce a sale

What Can Go Wrong? (And How to Avoid It)

  • Insufficient head height — You need 2.2m at the highest point as a minimum. Measure from the top of the existing ceiling joists to the ridge before getting excited about costs
  • Party wall issues — If your conversion affects a shared wall (semi/terraced), you need a Party Wall Agreement. Budget £700-£1,500 per neighbour and 2 months' notice
  • Staircase eating into the floor below — The new staircase has to go somewhere. In many homes, it takes space from a bedroom below, effectively losing a room to gain one
  • Water tank in the loft — Cold water tanks need relocating or replacing with a combi/system boiler. Budget £1,000-£3,000 for boiler changes
  • No building regs sign-off — Some cowboys skip building control. Without a completion certificate, you'll have problems selling the house. Always insist on it

Pro Tip: Before committing to any loft conversion, get a free feasibility visit from 2-3 specialist loft conversion companies. They'll assess your roof, measure head height, discuss the best type for your property, and give you a ballpark price — all for free. Only then should you pay for architectural drawings.

Frequently Asked Questions

How much does a loft conversion cost in the UK?

A loft conversion costs £15,000-£25,000 for a Velux (rooflight) conversion, £25,000-£50,000 for a rear dormer, £40,000-£65,000 for a hip-to-gable, and £45,000-£75,000 for a mansard in the UK in 2026. The type you need depends on your roof shape. Adding an en-suite costs an extra £3,000-£8,000. London prices are typically 30-50% higher than the national average.

Do I need planning permission for a loft conversion?

Most loft conversions (Velux and rear dormer) fall under Permitted Development and don't need planning permission, provided you stay within volume limits (40 m³ terraced, 50 m³ detached/semi) and don't extend beyond the existing roof plane facing a highway. Mansard conversions and properties in conservation areas almost always need planning. ALL loft conversions need building regulations approval regardless.

How long does a loft conversion take?

A Velux conversion takes 4-5 weeks on site. A rear dormer takes 5-7 weeks. A hip-to-gable takes 6-8 weeks. A mansard takes 7-10 weeks. Allow an additional 4-12 weeks before work starts for architectural drawings, structural calculations, building control applications, and planning permission (if needed). Total time from first enquiry to completion is typically 3-5 months.

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