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
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Loft conversion drawings · London Borough of Harrow

Loft conversion drawings in Harrow, £895 fixed

Harrow's Residential Design Guide SPD (adopted 15 December 2010) names as the preferred form of roof alteration to semi-detached or terraced houses extending a hipped roof to form a gable, with a rear roof extension or rear dormer window. For detached houses it says gabling existing hipped roofs can be unduly prominent and should be avoided.

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 Harrow Council asks of a loft conversion

From the council's Residential Design Guide SPD (adopted 15 December 2010, council page).

  • The preferred form of roof alteration to semi-detached or terraced houses is the extension of a hipped roof to form a gable with the addition of a rear roof extension (or a rear dormer window). (source, checked 15 October 2026)
  • To achieve visual containment within the roofslope, a rear roof extension (or dormer) must be set in at least 500mm from a shared (party) boundary with an attached house, set in at least 1000mm from the gable end, and set back at least 1000mm from the roof eaves measured externally along the roof slope. (source, checked 15 October 2026)
  • Where there is a rearward projecting pitched roof, the rear roof extension (or dormer) must leave a minimum of 500mm from the adjacent valley between the main and return roof slopes; where possible, setting its top down from the ridge (500mm recommended) gives further containment. (source, checked 15 October 2026)
  • Where a loft conversion is part of a two storey side extension, as a guide a single rear dormer should never be wider than could be created if an original hipped roof was altered to a gable end; in this case two or more separate dormers should be created with a minimum 500mm between them. (source, checked 15 October 2026)
  • For detached houses the gabling of existing hipped roofs can be unduly prominent and should be avoided; side and rear dormers may be an acceptable alternative. (source, checked 15 October 2026)
  • Generally, dormers should be subordinate features in the roof, should not overlap or wrap around the roof hips, and should never rise above the ridge. Floor-to-ceiling French doors or windows, possibly with railings creating a roof balcony, should be avoided. (source, checked 15 October 2026)

What Harrow loft conversion drawings have to show

Harrow's set-ins are measured on the roof, so the drawings mark the party boundary, the gable end, the eaves and any valley first. A rear roof extension or dormer must be set in at least 500mm from a shared boundary with an attached house, at least 1000mm from the gable end, and back at least 1000mm from the roof eaves, measured externally along the roof slope. Where there is a rearward projecting pitched roof it must leave at least 500mm from the valley between the main and return roof slopes. Setting its top down from the ridge, with 500mm recommended where possible, gives further containment.

Where the loft conversion is part of a two storey side extension, the guide says as a guide a single rear dormer should never be wider than could be created if an original hipped roof was altered to a gable end; two or more separate dormers should then be created with a minimum 500mm between them. Dormers should generally be subordinate features in the roof, should not overlap or wrap around the roof hips and should never rise above the ridge. Floor-to-ceiling French doors or windows, possibly with railings creating a roof balcony, should be avoided.

The council's requirements (checked 10 October 2026) list existing and proposed floor plans and elevations, site sections, finished floor and site levels, and roof plans, with the CIL form. Harrow has 30 conservation areas, and in the core of Pinnerwood Park Estate the Article 4 direction covers dormers and rooflights. A draft Small Sites Design Code, consulted on in 2021-22, proposed replacing the guide's householder section; the council's residential design page still links the 2010 guide (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

Harrow: 917 householder decisions

Harrow
Approvals, prior approvals included81.7%

749 of 917 granted. London: 85.8%.

Decided within 8 weeks94.5%

657 of 695 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 Harrow

  • Planning drawings: £895, plus £548 to Harrow 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 · Harrow planning rules · every price

Answers

Harrow loft conversion questions

Does Harrow allow hip-to-gable loft conversions?
Harrow's guide favours it on semi-detached and terraced houses: the preferred form of roof alteration is extending a hipped roof to form a gable with the addition of a rear roof extension or a rear dormer window. For detached houses the guide says gabling existing hipped roofs can be unduly prominent and should be avoided.
How far must a Harrow rear dormer be set in from the party wall and eaves?
The guide says a rear roof extension or dormer must be set in at least 500mm from a shared boundary with an attached house, at least 1000mm from the gable end, and back at least 1000mm from the roof eaves, measured externally along the roof slope. Next to a valley between main and return roofs it must leave at least 500mm.
Can I gable the hipped roof of a detached house in Harrow?
The guide says that for detached houses the gabling of existing hipped roofs can be unduly prominent and should be avoided, and that side and rear dormers may be an acceptable alternative. Generally, dormers should be subordinate features in the roof, should not overlap or wrap around the roof hips, and should never rise above the ridge.

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