Loft Conversions London, Surrey & Kent Expert Builders | 30+ Years | Free Site Visit


A loft conversion is one of the most cost-effective ways to add living space and value to a London home. For a typical 3-bedroom Victorian terrace in South London, a well-executed dormer conversion can add 15–20% to the property’s value – often more than it costs to build.

At J&D Building, we’ve been converting lofts across London, Surrey and Kent for over 30 years. Our projects range from straightforward Velux conversions (no planning permission required in most cases) to complex mansard builds on terraced properties in Conservation Areas. Call or text Jozeph directly: 07860 937539 – or read on to understand what’s involved.

  • Interior view of a roof structure showing wooden beams and a skylight being installed. London
  • Loft conversion Croydon - dormer construction in progress
  • View of a roof under construction with wooden beams and OSB boards laid out.
  • Construction workers lifting a beam during a renovation project in a brick building. High Wycombe
  • Two construction workers installing wooden beams on a building roof during renovation. Slough
  • View of an interior construction site showing wooden planks and an unfinished wall. - Watford
  • Interior view of a collapsed building showing exposed walls and debris on the floor.
  • A modern brick house featuring a glass extension and patio area.

Types of Loft Conversions

Dormer Loft Conversions

The most popular choice for Victorian terraced houses across London. A dormer conversion adds valuable headroom and creates a full-size bedroom with standing height throughout. Ideal for properties in Bromley, Croydon, Beckenham, and Victorian housing stock across the capital.

Dormer Loft Conversions — the most popular in South London


A dormer adds a vertical structure to the slope of your roof, creating full standing height across the entire loft floor. It’s the go-to choice for Victorian and Edwardian terraces across Croydon, Bromley, Sutton and Beckenham, where the original roof pitch often makes the raw loft too shallow to use comfortably.

  • Most popular type in South London terraces
  • Typically doesn’t require planning permission (permitted development)
  • Creates a full-size bedroom with en-suite or additional bathroom
  • Average build time: 6–10 weeks depending on specification
  • Typical cost range: £35,000–£55,000 (South London, 2025/26 prices)

Velux Loft Conversions — the most cost-effective option

If your loft has sufficient existing headroom (typically 2.3m+ from floor joist to ridge), a Velux conversion installs roof windows without altering the roof structure. No planning permission required in most cases. Fastest build time. Lowest cost.

  • No structural changes to roof shape
  • Often completed in 4–6 weeks
  • Typical cost range: £20,000–£35,000
  • Best for properties where planning permission would be difficult

Mansard Conversions — maximum space


A mansard conversion rebuilds the rear slope of the roof almost vertically, creating the maximum possible usable floor space. Common on terraced properties in Conservation Areas where a dormer would be refused — the mansard’s flat-top profile is more sympathetic to period streetscapes.

  • Requires planning permission
  • Creates the most floor space of any loft type
  • Typical cost range: £45,000–£75,000+
  • Often requires a party wall agreement in terraced properties


Hip-to-Gable Conversions — for semi-detached properties

Semi-detached and end-of-terrace properties often have a sloping ‘hip’ on the side. A hip-to-gable conversion extends this to a vertical wall, dramatically increasing the usable width of the loft. Often combined with a rear dormer for maximum space.

Service Areas

Loft conversions available within 30 miles of Central London:

Greater London:

  • All areas including Bromley, Croydon, Greenwich, Lewisham, Wimbledon, Kingston, Richmond

Surrey:

  • Reigate, Redhill, Dorking, Epsom, Ewell, Carshalton, Sutton, Banstead

Kent:

  • Sevenoaks, Orpington, Chislehurst, Sidcup, Dartford, Gravesend

Hertfordshire:

  • Watford, St Albans

Approximate costs (London & Home Counties, 2026)

Most dormer and Velux loft conversions fall under Permitted Development rights and don’t need planning permission, provided they meet specific conditions (size limits, materials, Conservation Area rules). We’ll confirm this during the initial site visit. Mansard conversions always require planning permission.

Velux conversions typically take 4–6 weeks. Dormer conversions take 6–10 weeks. Mansard and hip-to-gable conversions can take 10–14 weeks. These timelines assume standard Victorian or Edwardian construction — unusual structural conditions may add time.

Velux conversions typically take 4–6 weeks. Dormer conversions take 6–10 weeks. Mansard and hip-to-gable conversions can take 10–14 weeks. These timelines assume standard Victorian or Edwardian construction — unusual structural conditions may add time.

In most cases, no. Loft conversions are carried out from the roof down, with minimal disruption to the floors below. We aim to weatherproof the roof within 2–3 days of opening it, even in typical London weather.

We can advise on what’s likely to be approved and prepare drawings for Permitted Development confirmation. For full planning applications, we work with local architectural draughtspersons and can recommend trusted professionals.

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