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

01Hounslow, London

Mansard roof drawings in Hounslow

Hounslow will look at a mansard only where older houses nearby already carry the form, so the work starts with your neighbours' roofs and not with yours. We survey both, mark which roofs are original, altered or already mansarded, and draw the roof the guidance can support, from £845 including VAT.

From £845 (VAT included)

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    02The brief

    Precedent comes before design

    Hounslow's Residential Extension Guidelines treat mansard-style roofs as normally out of character. The one way in is a test about the street: historic precedent required. A house in a row of unaltered pitched roofs has nothing to point to, and a house beside two older mansards has a real case.

    That is why our first sheet is an evidence sheet. It records each neighbouring roof against the original, so the officer sees the same street you do and you see early whether the argument exists.

    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 Hounslow

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Mansard-style extensions normally out of character; may be allowed where older house styles and historic precedent exist.historic precedent requiredNo perioddemocraticservices.hounslow.gov.uk, Hounslow Residential Extension Guidelines SPD 2017, Mansard Slopes, p32
    Front dormers generally refused; extensions raising the ridge or full-width box forms normally refused.no front dormers; no ridge raiseNo perioddemocraticservices.hounslow.gov.uk, Hounslow Residential Extension Guidelines SPD 2017, Roof extensions, Position/Scale, p31
    Class AA, para AA.1(b)Class AA is not available on article 2(3) landNo periodlegislation.gov.uk
    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
    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
    Conservation areas33 named conservation areas published by the councilNo periodplanning.data.gov.uk
    Article 4 directions3 Article 4 directions published by the councilNo periodplanning.data.gov.uk
    Householder applications granted (PS2)74.7 % 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.

    Hounslow5 neighbouring councils
    Councils bordering Hounslow

    04The streets

    Householder applications by street in Hounslow

    Streets in Hounslow with the most householder applications, and the share approved
    StreetApplicationsApproved
    Firs Drive3761%
    Wood Lane3259%
    Park Drive3169%
    Parkwood Road2859%
    Worton Road2758%
    Arnold Crescent2654%
    Popes Lane2483%
    St Stephens Road2477%
    Whitton Dene2450%
    Harewood Road2378%
    Princes Avenue2382%
    Spring Grove Road2355%
    Fern Lane2268%
    Netheravon Road2273%
    North Hyde Lane2255%

    Counts of householder applications by street; no individual applications are shown. Streets with fewer than five applications are left out.

    GLA Planning London Datahub, householder applications

    05The drawing

    A mansard roof in sectionA, Hounslow: set-back and parapet: 1 m set-ins m. B, Permitted development and the eaves: Class B requires the original eaves to be maintained or reinstated, which a parapet-fronted mansard normally removes. C, Additional storeys under permitted development: Class AA additional storeys exclude houses built before 1 Jul 1948 or after 28 Oct 2018. D, 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)ABCD

    A mansard roof in section

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

    A Hounslow: set-back and parapet
    1 m set-ins m
    B Permitted development and the eaves
    Class B requires the original eaves to be maintained or reinstated, which a parapet-fronted mansard normally removes
    C Additional storeys under permitted development
    Class AA additional storeys exclude houses built before 1 Jul 1948 or after 28 Oct 2018
    D 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.

    06The detail

    Dormers at the front and boxes across the width

    On the form of the extension itself the guidance is brief: no front dormers; no ridge raise. Read alongside the rest of the wording, a scheme that lifts the ridge or fills the roof from side to side is the kind that gets refused.

    The practical result is that we test a rear roof design first. It keeps the street elevation untouched, and its set-ins from the sides, eaves and ridge are dimensioned on the elevation so nobody has to scale them off the drawing.

    Chiswick, Strand on the Green and where the controls bite

    The council publishes 33 conservation areas and 3 Article 4 directions. Chiswick shows how thick the layers get on one street. Hounslow Council states that Article 4 directions currently apply to the Gunnersbury and Bedford Park conservation areas. Strand on the Green carries more again: Strand on the Green's additional protections include the Thames Policy Area, Metropolitan Open Land (tideway and Oliver's Island) and an Architectural Priority Area.

    Permitted development is no shortcut. Class AA is not available on article 2(3) land, and Class B requires the original eaves to be maintained or reinstated, which a parapet-fronted mansard normally removes. A householder application is the route, and the Chiswick guide lists the conservation areas there.

    Two payments and one decision

    The council's householder fee is £548, and it goes to the council with the application. Our drawing fee starts at £845 including VAT, and a second chartered technologist reads the set before it is issued.

    Across the council's householder decisions in its statistical returns, 74.7% were grants. Every kind of householder scheme sits in that figure, so it tells you about the council and little about a mansard.

    Shared roofs and the stair underneath

    A terrace shares its roof structure with two neighbours and a semi with one, which brings the party wall procedure into play. Party structure notice at least 2 months before work. We draw the junctions with the shared walls so your surveyor has them from the start.

    The new storey also changes the escape route. 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 stair is drawn with that protected route from the first issue.

    A listed house needs listed building consent drawings in Hounslow as well as permission, and work below the house is a separate application, covered by basement conversion drawings in Hounslow.

    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.

    07The 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.

    08Correspondence

    Questions

    What counts as historic precedent for a mansard in Hounslow?

    The guidance puts it as historic precedent required. In practice that means older houses close to yours that already carry the form. We record them on the survey and tell you before you commit if the street offers none.

    Is a front dormer realistic on a Hounslow house?

    The guidance reads, in short, no front dormers; no ridge raise, so the front slope is the weaker case. A rear design is the one we would test first.

    Does a Chiswick address change the route?

    It adds controls. Class AA is not available on article 2(3) land, so an extra storey needs a planning application, and Article 4 directions can reach further. The free constraints check confirms which area your house falls in.

    My Hounslow house is listed. Is one application enough?

    No. A listed house needs listed building consent for the roof as well as planning permission, and the roof is treated as historic fabric. We read the list entry first.

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

    74.7%

    of householder decisions

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

    Photograph: Tanya Barrow

    09Further reading

    Other services in Hounslow

    Mansard roof drawings nearby

    10Sources

    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 Hounslow