Types of Loft Conversion London 2026: Complete Guide to Every Conversion Type

Choosing the right loft conversion type is the most important decision in any loft project. Each type suits different property styles, delivers different amounts of new floor space, has different planning permission requirements and costs different amounts. This guide sets out all five main loft conversion types in London for 2026 — Velux, dormer, L-shaped dormer, hip to gable and mansard — with costs, best property fits, planning rules and the pros and cons of each. LCCL Construction has delivered every loft conversion type across London and Hertfordshire for over 20 years.

LCCL Construction — specialists in all loft conversion types across London and Hertfordshire

1. Velux (Rooflight) Loft Conversion

Cost: £32,400 – £50,400 inc. VAT (£27,000 – £42,000 + VAT). The simplest and cheapest loft conversion type. Roof structure is unchanged — only rooflights (Velux windows) are installed. Best for properties with generous existing loft head height already. Falls within permitted development. Typically adds one bedroom, sometimes with ensuite. Pros: cheapest, quickest (8-10 weeks), no planning permission required in most cases. Cons: no extra floor space added, headroom limited to existing roof, unsuitable for many London properties with low pitched roofs.

2. Dormer Loft Conversion

Cost: £56,400 – £80,400 inc. VAT (£47,000 – £67,000 + VAT). The most popular type in London. A flat-roof dormer projects out from the rear of the existing roof, adding significant floor space and headroom. Best for terraced and semi-detached houses. Usually falls within permitted development. Typically adds one large bedroom with ensuite. Pros: excellent floor space uplift, straightforward planning, works on most Victorian and Edwardian terraces, cost-effective. Cons: box-like external appearance unless carefully designed. See our full dormer loft conversion guide.

3. L-Shaped Dormer Loft Conversion

Cost: £58,800 – £98,400 inc. VAT (£49,000 – £82,000 + VAT). Extends the dormer over both the main roof and the back addition roof (over the kitchen), creating an L-shape. Delivers substantially more floor space than a standard dormer. Best for Victorian and Edwardian terraces with rear back additions — the classic London terrace typology. Usually falls within permitted development. Typically creates two bedrooms plus ensuite. Pros: maximum floor space for a terraced property, excellent value per square metre, straightforward planning. Cons: only suitable for properties with a back addition. See our full L-shaped loft conversion guide.

4. Hip to Gable Loft Conversion

Cost: £60,000 – £114,000 inc. VAT (£50,000 – £95,000 + VAT). Transforms a hipped roof (sloping down on the side) into a vertical gable wall, dramatically increasing the usable floor space. Best for semi-detached, detached and end-of-terrace houses with hipped roofs — very common in 1930s London suburbs like Finchley, Southgate, Wembley, Ealing and Wimbledon. Usually falls within permitted development. Typically creates a master bedroom plus ensuite or two bedrooms. Often combined with a rear dormer for maximum space. Pros: massive floor space uplift on hipped-roof properties, excellent value. Cons: requires a hipped roof to begin with. See our full hip to gable loft conversion guide.

5. Mansard Loft Conversion

Cost: £76,800 – £148,800 inc. VAT (£64,000 – £124,000 + VAT). The most substantial loft conversion type. Rebuilds the entire roof structure with steep near-vertical walls and a flat roof on top, creating an almost full storey of new floor space. Best for premium Victorian and Georgian terraces in conservation areas (London councils often specifically require mansards to maintain streetscape character). Requires full planning permission almost always. Typically creates 2 bedrooms plus 2 ensuites. Pros: maximum floor space, elegant traditional appearance, highest property value uplift. Cons: most expensive, planning permission always required, longer timeline. See our full mansard loft conversion guide.

How to Choose the Right Loft Conversion Type

The right type depends on: your property style (terraced, semi-detached, detached, end-of-terrace); whether you have a back addition; roof pitch and existing head height; whether the property is in a conservation area or listed; how much floor space you want to add; whether you want to add one or two bedrooms; and your budget. LCCL Construction assesses all of these at the free initial consultation and recommends the best type for your specific property.

Comparison Table: All Loft Conversion Types

Velux: £27-42k, 1 bedroom, 8-10 weeks, no planning usually.

Dormer: £47-67k, 1 bedroom + ensuite, 10-12 weeks, PD usually.

L-Shaped: £49-82k, 2 bedrooms + ensuite, 12-14 weeks, PD usually.

Hip to Gable: £50-95k, 1-2 bedrooms + ensuite, 12-14 weeks, PD usually.

Mansard: £64-124k, 2 bedrooms + 2 ensuites, 14-16 weeks, planning required.

How Much Value Does Each Loft Conversion Type Add?

On our projects and local sold prices, a well-planned project of this kind usually adds more to the value of the home than it costs to build — see our guide on how much value an extension adds. Mansards typically deliver the highest total value uplift in premium London locations. L-shaped dormers deliver the best return per pound in most outer London locations. See our full guide on how much value a loft conversion adds and full loft conversion cost guide.

Frequently Asked Questions About Loft Conversion Types

Which loft conversion type is best value?

L-shaped dormer typically delivers the best value per square metre for Victorian terraces with back additions. Hip to gable is best for semi-detached and detached properties.

Do all loft conversions need planning permission?

No — Velux, dormer, L-shaped and hip to gable usually fall within permitted development rights. Mansards almost always require planning permission.

How do I know which type suits my property?

A free site consultation with a loft conversion specialist assesses your roof structure, head height, property style and planning constraints, then recommends the best type.

To book a free consultation call LCCL Construction on 020 8037 7332 or get an instant quote online.