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

01Islington, London

Mansard roof drawings in Islington

On an Islington terrace a roof extension is limited to a single storey and read against the parapet it sits behind. We draw the mansard as a whole roof, back included, from £845 including VAT, after a free constraints check.

From £845 (VAT included)

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    02The brief

    A single storey, and the right kind of mansard

    Islington's Urban Design Guide limits roof extensions on terraces and villas to 1 storey, and only where an extension is acceptable in principle. It adds that flat-topped mansards are usually not acceptable in conservation areas. The guide sets the flat-topped form against the traditional mansard, with its steep front and rear and shallow upper slope, and says dormer windows suit both.

    So the question for a terrace is not how many rooms the loft could hold. It is whether the proposal is the traditional form, at the permitted height, and that is what the section and elevation have to show.

    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 Islington

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Where acceptable in principle, roof extensions on terraces or villas are restricted to a single storey.1 storeyNo periodislington.gov.uk, Islington Urban Design Guide SPD (January 2017), roof extensions, para 5.154, PDF p.62
    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
    Approved Document K 2013, para 1.13, Diagram 1.4Loft conversions where 2.0 m cannot be achieved: 1.9 m at the centre of the stair, 1.8 m at the side (half width)No periodgov.uk
    Conservation areas41 named conservation areas published by the councilNo periodplanning.data.gov.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

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

    Islington4 neighbouring councils
    Councils bordering Islington

    04The streets

    Householder applications by street in Islington

    Streets in Islington with the most householder applications, and the share approved
    StreetApplicationsApproved
    Corbyn Street3585%
    Plimsoll Road2893%
    Aberdeen Park2491%
    Thorpedale Road2190%
    Highbury Hill2094%
    Hungerford Road2088%
    Sussex Way18100%
    Avenell Road1585%
    Hemingford Road1579%
    Huddleston Road15100%
    Romilly Road1592%
    Harberton Road14100%
    Offord Road1486%
    St George's Avenue14100%
    Thornhill Road1479%

    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, 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.

    06The detail

    Canonbury: what the area guidelines say about the back

    The Canonbury guidelines say the council will not permit new or enlarged dormers or rooflights on the front or side slopes of exposed pitched roofs, nor roof extensions on parapet roofs that are visible from the street or other public areas. Front slopes are therefore closed to dormers, and the design effort goes into the roof form itself.

    For a mansard the Canonbury guidelines add a second test. Traditional mansards, where permitted, must be mansarded at the rear too, not vertical brickwork, keeping the butterfly or original back profile. The rear elevation is read as closely as the street, so we draw both. The Canonbury guide lists the other controls on the same houses.

    Why the national routes stop short on a parapet roof

    A terrace roof behind a parapet is exactly what permitted development was not written for. Class B requires the original eaves to be maintained or reinstated, which a parapet-fronted mansard normally removes. The route for extra storeys is narrower again: Class AA additional storeys exclude houses built before 1 Jul 1948 or after 28 Oct 2018, and Class AA is not available on article 2(3) land.

    With 41 conservation areas in the borough, most terraces end up in a householder application. The council takes its own fee of £548 when you submit; ours is separate and is quoted before we start.

    Butterfly roofs, party walls and what the set shows

    The design guide asks for the extension to sit behind the retained historic parapet, to keep a butterfly profile where there is one, and for party walls to follow the roof form without a right-angled upstand. Those three points are the ones a section drawing settles, so we cut the section through the parapet and the party wall on the surveyed levels.

    A loft stair has to work before the roof does. On headroom, the national rule reads: Loft conversions where 2.0 m cannot be achieved: 1.9 m at the centre of the stair, 1.8 m at the side (half width). On insulation, new roof elements are held to limiting U-values: New 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 1.4.

    A listed house needs listed building consent drawings in Islington as well, and a lower floor is a separate scheme, covered by basement conversion drawings in Islington.

    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

    How high can a mansard go on an Islington terrace?

    The design guide restricts roof extensions on terraces and villas to 1 storey, where an extension is acceptable in principle at all. We check your terrace and the neighbouring roofs before drawing.

    Is a flat-topped roof extension acceptable in an Islington conservation area?

    The guide says flat-topped mansards are usually not acceptable in conservation areas, and describes the traditional mansard as the other main type. We draw the traditional form and tell you early if the street points elsewhere.

    Can I use Class AA instead of a planning application?

    Rarely. Class AA is not available on article 2(3) land, and Class AA additional storeys exclude houses built before 1 Jul 1948 or after 28 Oct 2018. The free constraints check tells you where your address stands.

    What does a butterfly roof change in a mansard design?

    The guide wants the original butterfly profile kept where it survives, with the new roof set behind the parapet. That fixes where the extension can start and how the party walls are finished, so we measure the valley and parapet heights before drawing.

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

    41

    named conservation areas published by the council

    Conservation areas, Islington. Source: planning.data.gov.uk

    Photograph: Tanya Barrow

    09Further reading

    Other services in Islington

    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 Islington