Types of Loft Conversion in London: Dormer, Hip-to-Gable, Mansard and More

A Velux or rooflight loft conversion does not add any new structure to the roof — the existing roof shape and pitch are retained, and natural light and access are provided solely through roof windows (Velux or equivalent) installed within the existing roof slope. Appropriate properties: a Velux conversion is only viable where the existing loft has adequate ridge height (typically 2.2m minimum between the ridge and the structural floor at the highest point, after the new floor structure has been installed) and adequate floor area within that height range. Many London Victorian terraces have steep-pitched roofs with adequate ridge height for a Velux conversion, but the usable floor area at the required head height is often limited. Usable floor space gained: because head height is constrained by the existing roof slope, a Velux conversion typically creates less usable floor space than a dormer conversion. The central area under the ridge is usable (standing height), but the sides of the room quickly slope down to eaves level. Typical usable area in a standard London Victorian terrace: 10-20m² at full standing height. Planning: a Velux conversion is usually permitted development (no planning permission required) — no external alteration to the existing roof is made (the roof windows are set within the existing plane of the roof and do not project significantly). Cost: £20,000-£35,000 for a Velux loft conversion in London (structural floor, stairs, roof windows, insulation, M&E first fix, plasterboard). Less expensive than a dormer because no new external structure is built. Best use: a small single bedroom or home office where budget is limited and planning constraints prohibit external alterations.

A rear dormer loft conversion is the most common type of loft conversion in London — it involves building a box-shaped extension to the rear slope of the roof, creating a vertical rear wall (the dormer face) and a flat or shallow-pitched dormer roof above. The dormer dramatically increases the usable floor space and ceiling height within the loft. Appropriate properties: virtually any London terraced or semi-detached property with a pitched roof that has space to build a rear dormer. The dormer is built on the rear slope only (not the front) — this is important for planning purposes. Planning for rear dormer in London: permitted development rules allow a rear dormer on a London terraced house provided it meets the following conditions: it does not exceed the highest point of the existing roof; it is set in from the sides (minimum 20cm from the eaves edge); it does not project beyond the rear wall of the original house at roof level; and the materials used for the dormer cladding are similar in appearance to the existing house (typically grey zinc or lead-effect materials for the dormer cheeks and roof). Conservation area: Article 4 Directions in most London conservation areas remove the PD right for rear dormers on terraces — planning permission is required. Rear dormers on conservation area properties are often approved if they are not visible from the street and materials are appropriate. Usable floor space gained: a full-width rear dormer on a typical London Victorian terrace creates 15-30m² of usable floor space at full ceiling height. This is typically enough for a double bedroom and an en-suite bathroom. Cost: £35,000-£70,000 for a rear dormer loft conversion in London (including stairs, bathroom, electrics, and plastering). One of the best-value space-creation projects in London.

A hip-to-gable loft conversion is applicable to London semi-detached properties and end-of-terrace houses where one side of the roof is a 'hip' (a sloping triangular face) rather than a vertical gable wall. The conversion involves replacing the hip with a new vertical gable wall — dramatically increasing the usable floor space at the side of the loft. Appropriate properties: London semi-detached houses (typically 1930s, 1940s, and 1950s build) and end-of-terrace Victorian and Edwardian houses with hipped roofs. The gable end is built on the flank wall of the property (the boundary side). Planning for hip-to-gable in London: a hip-to-gable conversion on a semi-detached London property is permitted development (PD) provided it meets the standard PD conditions. Important: only one hip can be converted to a gable under PD (the side furthest from the party wall, to avoid affecting the appearance of the pair). In a conservation area, Article 4 Directions typically require planning permission — the council will assess the impact on the character of the semi. Combination of hip-to-gable and rear dormer: the most common configuration for a London semi-detached loft conversion is the combination of a hip-to-gable extension and a full-width rear dormer. This creates the maximum possible usable floor space and can accommodate two bedrooms plus a bathroom in the loft of a standard 1930s semi. Usable floor space gained: a hip-to-gable plus rear dormer conversion on a typical London 1930s semi creates 25-40m² of new floor space. Cost: £50,000-£90,000 for a hip-to-gable plus rear dormer loft conversion in London.

A mansard loft conversion involves rebuilding the rear slope of the roof at a very steep angle (typically 70 degrees from horizontal) with a flat or very shallowly pitched roof at the top, replacing the original shallow-pitched rear slope. The result is a near-vertical rear wall at the top of the property, with a parapet at the eaves, creating the maximum possible room volume within the original footprint of the roof. Appropriate properties: London Victorian and Edwardian terraces where the maximum possible loft space is required. Mansard conversions are particularly prevalent in Central and Inner London (Kensington, Chelsea, Islington, Camden, Hackney) where properties are smaller but every square metre is extremely valuable. Planning for mansard in London: a mansard conversion is almost always not permitted development — the change to the roof form and appearance is significant and requires planning permission. In conservation areas, mansard conversions are often acceptable if they follow the established pattern of similar conversions on the terrace (a 'continuous mansard' where all houses in the terrace have converted to mansard is a very different planning consideration from a single isolated mansard in an otherwise unaltered terrace). Usable floor space gained: a full-width mansard on a typical London Victorian terrace creates 20-35m² of usable space at near-full ceiling height across the full width and depth of the loft — significantly more than a dormer. Cost: £60,000-£120,000 for a mansard loft conversion in London (more complex structurally than a dormer — the entire rear slope must be rebuilt). Higher cost but justified by maximum space creation in expensive London boroughs.

Many London Victorian terraced houses have a rear 'outrigger' (a narrower rear addition behind the main body of the house, containing the original kitchen or scullery at ground floor with a small bedroom above on the first floor). An L-shaped dormer loft conversion combines a main rear dormer over the main body of the house with a further smaller dormer over the outrigger roof — creating an L-shaped plan that dramatically increases the usable loft area. Appropriate properties: London Victorian terraces with a rear outrigger (very common in South and East London, and in many North London Victorian areas). The combined dormer creates a very large loft space because it uses the full rear depth of both the main house and the outrigger. Planning: generally permitted development if both elements meet the PD criteria. Conservation area: as with all dormers, Article 4 Directions require planning permission. L-shaped dormers on conservation area properties are assessed on their individual merits. Usable floor space gained: an L-shaped dormer on a typical London Victorian terrace with a two-room outrigger creates 25-45m² of new floor space — often enough for two bedrooms and a bathroom plus a separate bathroom. Cost: £55,000-£100,000 for an L-shaped dormer loft conversion in London. Excellent value for the space created because the outrigger section can be more economically built (shorter span, lower structure). The L-shaped loft layout is particularly effective for creating two separate bedrooms with privacy between them — the main dormer and the outrigger dormer are separated by the central structure of the house.