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Slate-clad roof extension on a yellow-brick London terraced house
Photograph: Daniel Sikpi

01Brent, London

Mansard roof drawings for Brent houses

A mansard adds a storey, and the roof rules we hold for Brent are written for dormers, so we draw a mansard against them as the closest local test. Our chartered architectural technologists (MCIAT) set the roof against both neighbours and the national limits, from £845 including VAT.

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    02The brief

    What Brent's roof guidance says, and what it does not

    The rules we hold for Brent roofs come from its Residential Extensions and Alterations Supplementary Planning Document and are written for dormers, not mansards. Read as the nearest local test, they say rear dormers can run to the full roof width, while front dormers are acceptable only where common in street. A mansard's front slope is a front roof change by nature, so on a street with no front dormers the second rule is the one to take seriously.

    Two limits sit alongside: a minimum clearance above the original eaves, and a depth cap for an L-shaped dormer measured against the rear outrigger. Both are in the table with their SPD paragraphs. A mansard is a different shape, so we show how it compares with each limit and the officer decides which test applies.

    Converted loft bedroom with roof windows and a Juliet balcony
    Rear view of brick terraced houses in London with slate roofs and chimney stacks along the shared roofline
    Photograph: Ben Hadfield

    03The record

    Local figures for Brent

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Rear and side dormers must sit at least 0.2 m above the original eaves; no dormer higher than the roof.0.2 m above eaves mNo periodbrent.gov.uk, Residential Extensions and Alterations SPD (adopted January 2025), paras 3.6.2, 3.6.5, 3.6.8
    Rear dormers may span the full width of the original roof.full roof widthNo periodbrent.gov.uk, Residential Extensions and Alterations SPD (adopted January 2025), para 3.6.7
    L-shaped dormers must not cover more than half the depth of the two-storey rear extension or outrigger.50% of outrigger depth %No periodbrent.gov.uk, Residential Extensions and Alterations SPD (adopted January 2025), paras 3.6.9-3.6.10
    Front dormers only acceptable where already a common feature of the street.only where common in streetNo periodbrent.gov.uk, Residential Extensions and Alterations SPD (adopted January 2025), para 3.6.3
    Class B, condition B.2(b)(i)(aa)Class B requires the original eaves to be maintained or reinstated, which a parapet-fronted mansard normally removesNo periodlegislation.gov.uk
    Class AA, para AA.1(c)Class AA additional storeys exclude houses built before 1 Jul 1948 or after 28 Oct 2018No periodlegislation.gov.uk
    Class AA, para AA.1(b)Class AA is not available on article 2(3) landNo periodlegislation.gov.uk
    Householder: alterations/extensions to a single dwellinghouse, from 1 Apr 2026548 GBPNo periodribblevalley.gov.uk
    Party Wall etc. Act 1996 s3(2)(a)Party structure notice at least 2 months before workNo periodlegislation.gov.uk
    Conservation areas23 named conservation areas published by the councilNo periodplanning.data.gov.uk
    Article 4 directions39 Article 4 directions published by the councilNo periodplanning.data.gov.uk
    Listed building entries93 list entries (Historic England, within the LPA boundary)No periodplanning.data.gov.uk
    Householder decisions (PS2)924 decisions2025 Q2 to 2026 Q1 (1 Apr 2025 to 31 Mar 2026)assets.publishing.service.gov.uk
    Householder applications granted (PS2)85.5 % of householder decisions2025 Q2 to 2026 Q1 (1 Apr 2025 to 31 Mar 2026)assets.publishing.service.gov.uk

    A blank value means the figure has not been published, not that there are none. Check your own address with the council.

    Brent7 neighbouring councils
    Councils bordering Brent

    04The drawing

    A mansard roof in sectionA, Permitted development and the eaves: Class B requires the original eaves to be maintained or reinstated, which a parapet-fronted mansard normally removes. B, Additional storeys under permitted development: Class AA additional storeys exclude houses built before 1 Jul 1948 or after 28 Oct 2018. C, Fire protection to the stair: New storey above 4.5 m by loft conversion: protect the full escape route with fire-resisting doors (min E 20) and partitions (min REI 30)ABC

    A mansard roof in section

    A London terrace with a mansard behind the parapet. The lettered marks show the limits the legend gives.

    A Permitted development and the eaves
    Class B requires the original eaves to be maintained or reinstated, which a parapet-fronted mansard normally removes
    B Additional storeys under permitted development
    Class AA additional storeys exclude houses built before 1 Jul 1948 or after 28 Oct 2018
    C Fire protection to the stair
    New storey above 4.5 m by loft conversion: protect the full escape route with fire-resisting doors (min E 20) and partitions (min REI 30)
    The mansard in three dimensions3D
    Scroll the page: the model turns with it.

    05The detail

    Why the permitted routes rarely suit a period house

    For a mansard the eaves test is the obstacle on Class B: Class B requires the original eaves to be maintained or reinstated, which a parapet-fronted mansard normally removes. Class AA is limited by date and by place. Class AA additional storeys exclude houses built before 1 Jul 1948 or after 28 Oct 2018, which rules out older houses, and Class AA is not available on article 2(3) land, which takes in Brent's 23 conservation areas.

    The council's recent returns record 0 granted and 0 refused under the upward-extension prior approval, so a planning application is the route we draw for.

    Householder planning in Brent

    Brent decides householder applications in volume: 924 over the four most recent quarterly returns, with 85.5% granted. That describes past decisions, not yours. The council's fee for a householder application is £548, paid to the council separately from ours.

    Where the work touches a shared wall, Party structure notice at least 2 months before work. We show that wall on the survey so the notice can be served on time.

    Listed houses and the rest of the heritage layer

    Brent holds 93 list entries and 39 Article 4 directions. A mansard on a listed house needs consent as well as planning permission, which is covered in listed building consent drawings in Brent. If the house also needs a lower floor, see basement conversion drawings in Brent, and for the wider picture read the mansard roof drawings hub.

    Planning sheet for a single-storey rear extension: proposed ground floor plan and rear elevation, with the Property Architecture title block
    Sample drawing. Proposed plan and rear elevation from a planning application set, sheet 03 at 1:50.

    06The papers

    What the drawings rest on

    Upper floors of a large yellow-brick Victorian house in London with chimney potsFlat conversions & change of use
    Photograph: Lorenc Memaga
    Loft floor plan marked up in an independent review, with three critical issues clouded and explained
    Sample drawing. A loft plan with the reviewer’s mark-up: stair pitch, dormer cheeks and roof ventilation.

    07Correspondence

    Questions

    Does Brent have a mansard policy?

    The roof rules we hold for Brent are written for dormers, so we treat them as the closest local test and ask the officer which applies. Where no local rule fits, the national limits and the building's own roofline decide the design.

    Can I use permitted development for a mansard in Brent?

    Seldom. Class B requires the original eaves to be maintained or reinstated, which a parapet-fronted mansard normally removes. Class AA excludes older houses: Class AA additional storeys exclude houses built before 1 Jul 1948 or after 28 Oct 2018.

    What does a mansard need beyond planning permission?

    Fire protection applies to the new storey: New storey above 4.5 m by loft conversion: protect the full escape route with fire-resisting doors (min E 20) and partitions (min REI 30). The drawings show the escape route so the building regulations stage starts from it.

    Brick cottage with a tiled roof, chimneys and a front dormer window

    85.5%

    of householder decisions

    Householder applications granted (PS2), Brent, 2025 Q2 to 2026 Q1 (1 Apr 2025 to 31 Mar 2026). Source: assets.publishing.service.gov.uk

    Photograph: Tanya Barrow

    08Further reading

    Other services in Brent

    Mansard roof drawings nearby

    09Sources

    Sources and dates

    Licences

    Kensington street lined with brick townhouses and lit streetlamps beneath an orange dusk sky

    Send us the address of your house.

    We look up the conservation area, listing and Article 4 position, then reply with a fixed fee. A message before 3pm is answered the same working day.

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    Mansard roof drawings in Brent