Loft Conversion Types for Wimbledon and Wandsworth Homes

Wimbledon and Wandsworth have a lot of loft conversions, and for good reason. The Victorian and Edwardian terraces of Southfields, Earlsfield, Wandsworth Common and South Wimbledon, and the inter-war semis towards Raynes Park, nearly all have roof space that can become a bedroom and bathroom.

The roof shape decides which type of loft you can build. Your council decides which type you're allowed to build. This guide goes through the main loft types, the national permitted development (PD) rules, and how Wandsworth and Merton guidance differs. Remember that SW19 straddles both boroughs.

The main types of loft conversion

Rooflight (Velux-style) conversion

The roof stays as it is and rooflights go into the slopes. It's the simplest option, but it only works where there's already enough head height under the ridge. Many London terraces don't have it. Rooflights usually fall under a separate, simpler PD class than dormers.

Rear dormer

A box-shaped extension on the rear roof slope with a near-vertical back wall. This is the standard loft for a mid-terrace in SW18 or SW19. It creates full head height across most of the room, enough for a double bedroom and often a shower room.

L-shaped dormer

A rear dormer on the main roof joined to a second dormer over the two-storey back addition. It gives the most space on a Victorian terrace, typically room for a bedroom plus a separate bathroom, but it also has the most impact on the neighbours, so councils look hard at its size.

Hip-to-gable

On a semi-detached or end-of-terrace house with a hipped (sloping) side roof, the hip is built up into a vertical gable wall, which extends the ridge. It's usually combined with a rear dormer. This is the typical loft on a 1930s semi.

Mansard

The rear slope is rebuilt at a steep angle, close to vertical, with a flat or shallow roof above. Party walls are often raised to enclose it, and windows sit in the steep slope. A mansard gives a lot of space but changes the roof the most, so it's the type most likely to need full planning permission.

The national PD rules for lofts

Under Class B of the government's householder PD technical guidance, and as summarised on the Planning Portal, a roof extension is PD only if:

• it adds no more than 40 m³ to the original roof space of a terraced house, or 50 m³ for a semi or detached house, including any earlier roof extensions;
• no part rises above the highest part of the existing roof;
• nothing projects beyond the roof slope at the front of the house where it faces a road, so front dormers need permission;
• materials look similar to the existing house;
• apart from hip-to-gable work, the dormer is set back at least 0.2 m from the eaves where practicable and doesn't overhang the outer wall;
• there are no balconies or raised platforms;
• side-facing windows are obscure-glazed and fixed shut below 1.7 m from the floor; and
• the house isn't in a conservation area, where roof extensions aren't PD at all.

Flats and maisonettes have no Class B rights. If your house has been split into flats, any dormer needs planning permission.

Most owners confirm a PD loft with a Lawful Development Certificate. It costs £274 in England from April 2026 (a householder application is £548), according to the government fee schedule. Our guide to lawful development certificates for lofts covers how often they're refused locally and why.

Wandsworth: what the Housing SPD says about each type

Wandsworth's Housing SPD (adopted November 2016) is unusually detailed about roofs:

• Rear dormers and mansard-style additions on mid-terraces. On a mid-terrace where the party walls rise through the roof, the SPD describes a full-width "mansard-style" extension on the rear slope, with traditionally detailed dormers, as the simplest and most efficient approach. It says these additions are "usually acceptable where these cannot be clearly seen from the street", and it favours a sloping face of about 70 degrees over a sheer vertical wall.
• Corner and end-of-terrace houses. The SPD says a rear mansard-style addition should be avoided on these houses, because the change to the gable would be visible from the street. A well-proportioned rear dormer, set below the ridge and in from the edge, is recommended instead.
• Over the back addition (L-shaped). To limit the impact on the neighbour, the SPD suggests keeping the extension over the back addition to less than half the back addition's length.
• Hip-to-gable. Don't convert a hip where it would spoil a consistent roofscape. On corners, a hip-to-gable (if acceptable) shouldn't be combined with a rear mansard. And the SPD says hip-to-gable conversions are "generally not acceptable in conservation areas".
• Proper mansards. Adding a mansard that can be seen from public areas in a conservation area is "unlikely" to be acceptable.

Wandsworth has 46 conservation areas, eight of them with Article 4 Directions. Our Wandsworth loft conversions page and our Southfields loft conversion show what a typical SW18 rear dormer involves.

Merton (most of Wimbledon): what to expect

Merton's permitted development page points to the national rules and reminds owners that PD doesn't apply to flats or listed buildings, and that conservation areas carry extra restrictions. Merton adopted a new Local Plan in November 2024.

The Wimbledon conservation areas include Wimbledon North, Wimbledon Village, Wimbledon West, Wimbledon Hill Road, Merton Hall Road, Dunmore Road and others on the council's conservation areas list. In any of them, a dormer needs a householder application.

In John Innes Merton Park and Wilton Crescent, Article 4 Directions apply on top. The council's John Innes design guide says "any dormer should be located on the rear roof slope, set back from the eaves and should not project above the ridge line". Our Wimbledon loft conversions page covers the SW19 side in more detail.

One Merton point to watch on big combined schemes: if a loft plus an extension adds 100 m² or more of floor space, the Community Infrastructure Levy can apply, and the householder exemption must be claimed before work starts.

Which loft suits which house?

House	Usual option	PD outside conservation areas?	Watch-outs
Mid-terrace, SW18/SW19	Rear dormer; L-shaped if space allows	Often, within 40 m³	Previous dormers count towards the volume; 0.2 m eaves set-back
Mid-terrace wanting maximum space	Mansard-style rear addition	Sometimes; often needs an application	Wandsworth favours it on mid-terraces not visible from the street
End-of-terrace / corner	Rear dormer kept in from the gable	Often	Wandsworth advises against rear mansards here
1930s semi (Raynes Park, Wimbledon Park)	Hip-to-gable + rear dormer	Often, within 50 m³	Not PD in conservation areas; councils resist breaking a matching pair
Flat or maisonette	Any dormer	No	Planning permission plus freeholder consent

Building regulations: the bits that surprise people

Planning is only half of it. Every loft conversion needs building regulations approval. The Planning Portal's guidance on loft fire safety explains that a typical loft on a two-storey house usually needs fire-resisting doors protecting the stairway and mains-powered, interlinked smoke alarms on each level, because escaping through windows above first floor is too dangerous. Its stairs guidance says retractable ladders aren't normally acceptable. Where the new stair lands often decides the whole layout, so settle it before the dormer size.

Most terrace lofts also involve the Party Wall Act, because steels are usually built into the shared walls. That means serving notice on the neighbours before work starts.

FAQ

Which type of loft conversion adds the most space?

On a Victorian terrace, an L-shaped dormer or a mansard-style rear addition usually adds the most. On a semi, a hip-to-gable with a rear dormer does. Which one you can build depends on PD limits, conservation area status and council guidance.

Do I need planning permission for a dormer loft in Wandsworth or Wimbledon?

Not if it meets the Class B PD limits and the house isn't in a conservation area, isn't a flat and isn't covered by an Article 4 Direction removing roof rights. Otherwise you'll need a householder application.

Is a mansard loft allowed in Wandsworth?

Wandsworth's Housing SPD says mansard-style rear additions on mid-terraces are usually acceptable where they can't be clearly seen from the street. It advises against them on corner and end-of-terrace houses and in visible positions in conservation areas.

Can I do a hip-to-gable loft conversion in a conservation area?

It isn't permitted development in a conservation area, and Wandsworth's SPD says hip-to-gable conversions there are generally not acceptable. In Merton, the John Innes design guide expects dormers on the rear slope that keep the roof form.

Does a loft conversion need building regulations approval?

Yes. Expect requirements on structure, insulation, a proper staircase and fire safety, usually including fire-resisting doors to the stairway and interlinked smoke alarms.

Planning a loft in SW18 or SW19?

We build loft conversions across Wandsworth and Wimbledon. Call 07564 041115 or email admin@bluebirdspaces.co.uk to talk through what your roof can take.

General guidance, not planning advice. Always confirm with your council. Sources checked 4 October 2026.