Two Victorian terraced houses on a London street, one painted white and one in yellow stock brick, with bay windows
Floor plan drawings, pencil sketches of a house, a scale rule and a protractor spread across a desk
Photo: Tima Miroshnichenko / Pexels

Loft conversion drawings · London Borough of Southwark

Loft conversion drawings in Southwark, £895 fixed

Southwark's Householder Development SPD (adopted 7 July 2025) says rear dormers in conservation areas should be at least 0.5m below the ridge, 1m above the eaves, and set in 1m from the shared boundary and from the edge of the roof. Box dormers or overly large dormers will not be permitted in conservation areas or for listed buildings.

Planning drawings£895
Building regs£795
Lawfulnessfrom £950
Council fee£548
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Boroughs33/33
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Photo: Huy Phan / Pexels

Dormer loft conversions clad in dark tiles on the backs of yellow-brick London terraced houses at sunset
A dormer loft conversion on a London terrace. Photo: Daniel Sikpi / Pexels.

What Southwark Council asks of a loft conversion

From the council's Householder Development SPD (adopted 7 July 2025, council page).

  • Rear dormers in conservation areas should be symmetrically located, at least 0.5m below the ridge of the roof, 1m above the eaves, and set in 1m from the shared boundary and from the edge of the roof. (source, checked 15 October 2026)
  • Box dormers or overly large dormers will not be permitted in conservation areas or for listed buildings, as they are not seen as sympathetic to the historic character of these homes. (source, checked 15 October 2026)
  • Mansard extensions should be designed to sit behind the front and rear parapet and be at a maximum angle of 70 degrees; on a street corner the mansard should return to match the parapet. Mansard extensions will not be permitted if extending onto an outrigger. (source, checked 15 October 2026)
  • A mansard extension will not be permitted if it disrupts the consistency of surrounding roof forms; for example, it would not be permitted where there is an unbroken run of butterfly roofs. (source, checked 15 October 2026)
  • Raising the ridge is not encouraged, especially in a conservation area. A ridge raise should keep the slope of the front roof the same, extending it upwards by no more than 300-400mm with the gradient unaltered, contained within any roof chimneys and in like-for-like materials. (source, checked 15 October 2026)
  • Side dormers are not encouraged unless they are an original or common feature of properties in the street, and should sit within the slope of the roof, well clear of any hips and verges. (source, checked 15 October 2026)

What Southwark loft conversion drawings have to show

Southwark's dormer figures are measured on the existing roof, so the drawings mark the ridge, the eaves, the shared boundary and the edge of the roof before the dormer goes on. For conservation areas the SPD says a rear dormer should be symmetrically located, at least 0.5m below the ridge, 1m above the eaves, and set in 1m from the shared boundary and from the edge of the roof. Box dormers or overly large dormers will not be permitted in conservation areas or for listed buildings. Side dormers are not encouraged unless they are an original or common feature of properties in the street, and should sit within the slope of the roof, well clear of any hips and verges.

A mansard is drawn to sit behind the front and rear parapet at a maximum angle of 70 degrees, returning to match the parapet on a street corner. The SPD says a mansard will not be permitted if it extends onto an outrigger, or if it disrupts the consistency of surrounding roof forms, for example where there is an unbroken run of butterfly roofs. Raising the ridge is not encouraged, especially in a conservation area. A ridge raise should keep the slope of the front roof the same, extending it upwards by no more than 300-400mm with the gradient unaltered, contained within any roof chimneys and in like-for-like materials.

The council's householder checklist (checked 10 October 2026) asks for a fire safety strategy or a reasonable exception form (London Plan Policy D12) and CIL information with every application, and a site plan at 1:100 or 1:50 that labels and numbers every immediately adjoining building, with elevations of the front, back and both sides. On the Sunray Estate Conservation Area, external alterations on Sunray Avenue, Sunray Gardens, Casino Avenue, Nairne Grove and parts of Red Post Hill and Herne Hill need planning permission under a direction confirmed on 13 November 1987. The SPD was adopted on 7 July 2025, and we checked it on 15 October 2026.

The national permitted development volume limits (40 cubic metres on a terrace, 50 on a semi-detached or detached house: GPDO 2015, Schedule 2, Part 1, Class B) and the fire escape rules for a new second floor are the same in every borough. They are set out with diagrams on our loft conversion drawings page.

PS2 · at a glance

Southwark: 558 householder decisions

Southwark
Approvals, prior approvals included94.8%

529 of 558 granted. London: 85.8%.

Decided within 8 weeks97.5%

424 of 435 applications, prior approvals excluded.

Source: MHCLG PS2, 1 July 2025 to 30 June 2026. Dark tick: London.
A finished loft room with a sloping ceiling, two roof windows and a light wood floor
A finished loft room: the headroom, the roof windows and the stair opening are all set out on the drawings. Photo: Liam Gillan / Pexels.

What it costs in Southwark

  • Planning drawings: £895, plus £548 to Southwark Council.
  • Certificate of lawfulness where the loft is permitted development: from £950, plus £274 to the council.
  • Building regulations drawings: £795.

Loft conversion drawings across London · Southwark planning rules · every price

Answers

Southwark loft conversion questions

Can I build a mansard on a Southwark terrace with butterfly roofs?
Not where there is an unbroken run of butterfly roofs: the SPD says a mansard will not be permitted if it disrupts the consistency of surrounding roof forms. Mansards should sit behind the front and rear parapet at a maximum angle of 70 degrees, and will not be permitted if extending onto an outrigger.
What size can a rear dormer be in a Southwark conservation area?
Rear dormers in conservation areas should be symmetrically located, at least 0.5m below the ridge, 1m above the eaves, and set in 1m from the shared boundary and from the edge of the roof, the SPD says. Box dormers or overly large dormers will not be permitted in conservation areas or for listed buildings.
How much can I raise the ridge in Southwark?
Raising the ridge is not encouraged, the SPD says, especially in a conservation area. A ridge raise should keep the slope of the front roof the same, extending it upwards by no more than 300-400mm with the gradient unaltered, contained within any roof chimneys and in like-for-like materials.

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