Barnet's new guidance tells owners to use permitted development for a rear dormer where they can, and sets firm set-ins where they cannot. Most of our Barnet lofts start with that one decision.
Photo: Maxwell Hamilton, BY 2.0
Paragraph 4.86 of Barnet's new SPD is unusually direct: if permitted development rights exist at the house, the applicant can exercise them, as long as the rear dormer meets the limits and conditions of permitted development. Under Class B that means up to 40 cubic metres of extra roof space on a terrace and 50 on a semi or detached house, nothing above the ridge, nothing on the front slope, and materials of similar appearance.
Where rights do not exist, because the house is in a conservation area, is a flat, or has had its rights removed, the dormer needs planning permission and paragraph 4.87 applies. It should then be inset from the eaves, the ridge and the edges of the original roof by at least 0.5 metres. Larger roofs, roofs already extended and houses in prominent spots should increase those set-ins or use smaller, spaced dormers.
Paragraph 4.89 adds a practical point: if a rear dormer cannot be set down from the ridge because of building control head-height requirements, Barnet wants a section drawing that proves the internal ceiling heights. We draw that section as standard, because it is the drawing that stops the question being asked.
From Part 4 of the June 2026 SPD.
| Roof work | Barnet's test | Paragraph |
|---|---|---|
| Hip to gable | Permitted development where rights exist; otherwise to re-balance a pair or short terrace | 4.83 to 4.84 |
| Front dormer | Generally not supported unless common in the street | 4.85 |
| Rear dormer | Inset 0.5 m from eaves, ridge and roof edges | 4.87 |
| Side dormer | 0.5 m up from the eaves; obscure glazed to 1.7 m | 4.90 to 4.92 |
| L-shaped dormer | At most 50% of the original outrigger; 0.5 m from eaves and ridge | 4.95 to 4.96 |
Barnet Council, Sustainable Design and Development Guidance SPD, Part 4, adopted 15 June 2026.
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Much of Barnet is interwar semis with hipped roofs, so hip to gable is the commonest loft we draw here. The SPD confirms that an original hipped roof can be converted to a gable under permitted development. Where it cannot, Barnet will generally accept one that re-balances a pair of semis whose other half already has a gable, or a short terrace whose end house does.
L-shaped dormers over a two-storey outrigger follow the same two-route logic. With permitted development rights, and an outrigger that is part of the original house, the L can be built within the Class B limits. Without them, and only where L-shapes are typical of the area, it should cover no more than half of the outrigger's depth, be set 0.5 metres up from the eaves on all sides and 0.5 metres down from the ridge. Barnet warns that L-shapes can give the effect of a third storey.
Barnet lists 16 conservation areas, including Hampstead Garden Suburb, Finchley Garden Village and Monken Hadley, and 10 of them are covered by Article 4 directions. There, a loft needs a full application. Barnet decided 1,136 householder applications in the year to June 2026, prior approvals aside, and 1,081 within 8 weeks.
Every figure is linked to the page or document we read.
Barnet's SPD, adopted on 15 June 2026, says a rear dormer that is not permitted development should be inset from the eaves, ridge and edges of the original roof by at least 0.5 metres.
Source: Barnet Council, SPD Part 4, paragraph 4.87An L-shaped dormer needing permission in Barnet should not extend more than 50% of the depth of the original outrigger.
Source: Barnet Council, SPD Part 4, paragraph 4.95Side dormer windows in Barnet must be obscure glazed up to 1.7 metres above finished floor level and set at least 0.5 metres up from the eaves.
Source: Barnet Council, SPD Part 4, paragraphs 4.90 and 4.92Barnet lists 16 conservation areas, and 10 of them are covered by or have Article 4 directions in force.
Source: Barnet Council, Conservation areasSince 29 May 2016 planning permission has been required anywhere in Barnet to change a house (C3) into a small house in multiple occupation (C4).
Source: Barnet Council, Article 4 Directions in BarnetBarnet decided 1,136 householder applications between July 2025 and June 2026, prior approvals excluded, and 1,081 of them were decided within 8 weeks.
Source: MHCLG, Planning application statistics PS2, July 2025 to June 2026Class B permits a roof extension of up to 40 cubic metres on a terraced house and 50 cubic metres in any other case.
Source: legislation.gov.uk, GPDO 2015, Schedule 2, Part 1, Class BTell us about your project and get a fixed, no-obligation quote back within one working day. If you don't need planning permission at all, we'll tell you that too — for free.
Yes, where the rights exist. Paragraph 4.86 of the June 2026 SPD says you can exercise them as long as the dormer meets the permitted development limits, which under Class B means 40 cubic metres on a terrace or 50 on other houses.
At least 0.5 metres from the eaves, the ridge and the edges of the original roof, more on large or prominent roofs. If the dormer cannot drop below the ridge for head height, Barnet asks for a section showing the internal ceiling heights.
Under permitted development, usually yes. Where it needs permission, the SPD says a hip to gable is generally acceptable when it re-balances a pair of semis whose attached house already has a gable, or a short terrace whose end house has one.
Generally not. Paragraph 4.85 says front dormers will only be acceptable where they are a common feature of the street and do not unbalance the adjoining houses. We usually design for the rear slope and use rooflights at the front.
£765 inc survey (£565 if you supply measured drawings). That covers the measured survey, the drawings and the submission or certificate, with free revisions until the council decides. Barnet's own fee is separate and goes to the council.
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