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

01Mansards, extensions and basements

Mansard roof drawings for period homes in London

A mansard turns the loft of a Georgian or Victorian terrace into a full storey, and on a period street the council reads your roofline as part of the whole terrace. Our chartered architectural technologists (MCIAT) draw it to that test, from £845 including VAT.

From £845 (VAT included)

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    02The brief

    Why a mansard is judged against the whole terrace

    A mansard replaces the pitched roof with a near-vertical lower slope, a flatter upper slope and dormers, so the new storey sits where the loft was. Planning permission is the usual route: Class B permitted development needs the original eaves kept, and a parapet-fronted mansard normally removes them.

    On a street of period houses the officer compares your roof with its neighbours before anything else. Kensington and Chelsea shows how that works: its roof policy tests each change in short as sympathetic to group, and it accepts an extra storey where the new roof could infill compromised terraces.

    Brick cottage with a tiled roof, chimneys and a front dormer window
    Upper floors of a large yellow-brick Victorian house in London with chimney pots
    Photograph: Lorenc Memaga

    03The record

    The national rules in figures

    Figures with their unit, period and source
    MeasureValuePeriodSource
    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
    Approved Document B Vol 1, para 2.21New 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)No periodgov.uk
    Approved Document L Vol 1 2021 incl. 2023 amendments, Table 4.2New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4No periodgov.uk
    Conservation areas40 named conservation areas published by the councilNo periodplanning.data.gov.uk
    Conservation areas39 named conservation areas published by the councilNo periodplanning.data.gov.uk
    Article 4 directions84 Article 4 directions published by the councilNo periodplanning.data.gov.uk

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

    London33 councils
    Councils on this page

    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

    Conservation areas, Article 4 and listed houses

    Most period terraces sit inside a designated area. Camden publishes 40 conservation areas and 21 Article 4 directions, and Kensington and Chelsea publishes 39 and 84. Class AA, the upward-extension class, is not available on article 2(3) land, so a conservation area means a householder planning application.

    Read the local rules for your borough on pages such as mansard roof drawings in Camden and mansard roof drawings in Kensington and Chelsea. A listed house adds a second consent, covered under listed building consent drawings.

    What resists a mansard, and what helps

    Councils resist a new storey most firmly where the roofline is unbroken. Kensington and Chelsea lists 9 resistance criteria for extra storeys, among them unimpaired rooflines, buildings that already have a mansard and pitched roofs with eaves.

    Helpful evidence is the opposite: a terrace already broken up by varied roof extensions, and a design that keeps the dormers the street already has. The same policy says to retain historic dormers, so we survey and draw those before we propose anything.

    What the drawing set contains

    Existing and proposed plans, sections and elevations of the roof, set on one surveyed datum, plus the roofline shown against both neighbours. The Party Wall etc. Act 1996 sets the notice period: Party structure notice at least 2 months before work.

    The set also shows the protected escape route under Approved Document B Volume 1 and the stair headroom the loft needs. The council's householder fee for a house is £548, paid to the council separately from our fee.

    Period neighbourhoods we draw in

    Terrace roofs behave differently street by street. For a house in one of the conservation areas of Hampstead, start with architectural drawings in Hampstead, where the local Article 4 directions and conservation area statement are set out. A basement under the same house is a separate application, covered by basement conversion drawings.

    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

    Rear view of brick terraced houses in London with slate roofs and chimney stacks along the shared rooflineParty wall services
    Photograph: Ben Hadfield
    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

    Do I need planning permission for a mansard roof in London?

    Almost always. Class B does not suit a mansard because it requires the original eaves to be kept, and Class AA is not available on article 2(3) land, which takes in conservation areas. Householder planning permission is the normal route, and we confirm it in a free constraints check before quoting.

    Can a mansard be added to a listed house?

    Only with listed building consent as well as planning permission, and with the roof treated as historic fabric. Listed building consent drawings explains the extra assessment of significance that the application needs.

    What does the fixed fee for mansard roof drawings cover?

    Our fee starts at £845 including VAT and covers the surveyed and proposed drawings for the application. Council application fees are separate, and every set is checked by a second technologist before it goes in.

    Why do some councils refuse an extra storey on a terrace?

    Because an unbroken roofline is part of the terrace's character. Kensington and Chelsea lists 9 resistance criteria, and its guidance says to resist an extra storey on a building that already has a mansard. We tell you early if your street falls into one of those cases.

    Converted loft bedroom with roof windows and a Juliet balcony
    Photograph: Imad Clicks

    08Further reading

    London

    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 for London period homes