Loft Conversion Cost UK 2026: What Builders Charge by Type

Quick Answer

Loft conversions in the UK cost £20,000–£35,000 for a basic Velux (rooflight) conversion, £35,000–£55,000 for a dormer conversion, £45,000–£70,000 for a hip-to-gable, and £50,000–£80,000+ for a mansard conversion. These prices cover structural work, insulation, staircase, electrics, plumbing (if adding a bathroom), and basic plastering — but typically exclude fitted furniture, decoration, and high-spec finishes. London and the South East add 20–30% to these figures.

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The Four Main Types of Loft Conversion

1. Velux (Rooflight) Conversion

The simplest and cheapest option — the existing roof structure is retained and Velux skylights are added. No structural change to the roofline.

When it works: Roof has sufficient pitch and headroom (minimum 2.2m at the ridge). Most suitable for detached and semi-detached houses where the existing roof already provides adequate space.

Cost: £20,000–£35,000

Pros: Cheapest option; usually doesn't require planning permission; minimal structural disruption; quickest to complete (6–10 weeks)

Cons: Limited headroom compared to other types; can't extend the usable footprint

2. Dormer Conversion

A box-shaped structure is added to the existing roof slope, creating additional headroom and floor space. The most popular loft conversion type in the UK.

When it works: Almost any property — semi-detached, terrace, or detached. The dormer extends the rear roof slope (usually).

Cost: £35,000–£55,000 for a standard single dormer; £45,000–£65,000 for a full-width rear dormer

Pros: Significantly increases usable floor space; allows full-height ceilings throughout; relatively straightforward for builders experienced in loft conversions

Cons: More expensive than Velux; typically requires planning permission (though some dormer extensions are permitted development)

3. Hip-to-Gable Conversion

The sloping hip end of the roof is replaced with a vertical gable wall, creating more usable space at the end of the property. Often combined with a rear dormer.

When it works: Detached or end-of-terrace houses with a hipped roof. Very common on 1930s–1950s semi-detached properties.

Cost: £45,000–£70,000 (often includes a rear dormer)

Pros: Maximises usable floor space; can dramatically increase headroom; suited to properties where a dormer alone wouldn't provide enough space

Cons: Significant structural work; almost always requires planning permission; longer build time

4. Mansard Conversion

The most extensive type — one or both sides of the roof are restructured to create near-vertical walls with a shallow pitch at the top. Primarily used in London and for period properties.

Cost: £50,000–£80,000+

Pros: Creates maximum floor space; suitable for terraced properties in dense urban areas; most architecturally suited to Victorian and Edwardian buildings

Cons: Most expensive option; always requires planning permission; significant structural work; common in London, rare elsewhere

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What's Included in a Loft Conversion Quote

A complete loft conversion quote should cover:

• Structural work: steel beams, joist strengthening, structural calculations
• Roof alterations: dormer construction, Velux installation, new felt and battens
• Insulation: between and below joists to Part L Building Regulations standard
• Staircase: new loft staircase (regulations require this to be a permanent, permanent-access staircase with minimum 2m headroom)
• Electrics: lighting, sockets, smoke detectors, possibly a new consumer unit circuit
• Plumbing: if adding an en-suite bathroom (often included in a bathroom allowance)
• Plastering: walls and ceiling to smooth finish
• Flooring screed or boarding: to structural floor finish (not including finished floor covering)
• Party wall work: if applicable (usually separate cost for surveyor)
• Building regulations: application, inspections, and completion certificate

What's typically NOT included: floor coverings, bathroom fittings and tiles, fitted wardrobes, decoration, furniture, and Juliet balconies or feature glazing.

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Labour Rates: What Loft Conversion Builders Charge

Loft conversions involve multiple trades — structural engineers, carpenters, bricklayers (for dormer walls), roofers, electricians, and plumbers. Main contractor day rates:

A loft conversion is almost always contracted as a fixed-price job with a main contractor who manages the trades. This is the correct approach — managing multiple subcontractors yourself as a first-time client introduces significant risk.

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Does a Loft Conversion Need Planning Permission?

Velux conversions: Usually permitted development (no planning permission required) in England, provided the roof windows don't protrude more than 150mm beyond the existing roof plane.

Rear dormers: Permitted development in most cases for single-family dwellings in England, provided they don't exceed 40m³ (terraces) or 50m³ (other houses) of additional volume, and don't protrude above the existing ridge line.

Hip-to-gable and mansard: Almost always require full planning permission.

London boroughs and conservation areas: Article 4 Directions remove permitted development rights in many areas. Always check with your local planning authority before assuming permitted development applies.

Building regulations approval is required for all loft conversions regardless of planning requirements — this covers structural safety, fire escape, thermal performance, and staircase standards.

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How Long Does a Loft Conversion Take?

These include building regulations inspections at key stages. Weather delays and material supply issues can extend timelines, particularly for roofwork.

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Adding Value: Return on Investment

A well-executed loft conversion typically adds 15–25% to a property's value. In areas where an additional bedroom significantly changes the property's market position (e.g. converting a 2-bed to a 3-bed in a family neighbourhood), the return can be higher.

At current conversion costs, a £40,000 dormer conversion that adds £60,000–£80,000 of value represents a strong return. However, this varies significantly by location — in areas where property prices are lower, the value added may not recover the conversion cost. Always research your local market before committing.

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Frequently Asked Questions

Do I need to tell my mortgage lender about a loft conversion? Yes — you should inform your mortgage lender before starting work, as the conversion increases the property's value and changes its structure. Most lenders are supportive but need to be notified. Check with your buildings insurer too.

Can I do a loft conversion myself? Some elements — boarding the loft, basic insulation — can be DIY. Structural work, roofing, gas and electrical work, and anything requiring building regulations sign-off must be done by qualified professionals. A DIY loft conversion without proper building regulations certification will cause significant problems when you come to sell.

How much does an en-suite add to a loft conversion cost? A basic en-suite (shower, basin, toilet) adds £4,000–£8,000 to the conversion cost. A high-spec en-suite with premium fixtures can add £10,000–£15,000+.

What headroom do I need for a loft conversion? Building regulations require a minimum height of 2.2m at the ridge (highest point) for the conversion to be habitable. A qualified surveyor or builder can measure your existing loft to advise whether it's viable without structural changes.

Will a loft conversion affect my neighbours? If you share a wall with neighbours (terraced or semi-detached), the Party Wall Act 1996 applies to structural work within 3–6 metres of the party wall. You'll need to serve a party wall notice and potentially pay for a party wall surveyor if neighbours dispute the work. Budget £500–£1,500 per adjoining property for party wall surveying.