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Hounslow, London

L-shaped dormer drawings in Hounslow

L-shaped dormer drawings in Hounslow have to answer a rule most boroughs do not state so bluntly: the council wants side and rear dormers to stay independent, not wrap round into one large extension. An L runs close to that line, so the drawings are where the case is won or lost.

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    Architectural model of a four-storey London stucco townhouse in its terrace, with a portico, area railings, sash windows, a cornice and chimney stacks
    The house as it stands: four storeys over a lower ground floor.Existing Proposed worksAn illustrative model, built for this page.

    How we work on l-shaped dormer drawings

    Nine steps from first call to approval.

    The same model cut through the middle: every floor, the stair, the chimney breasts, the new mansard, rear extension and basement in section
    Section through the model: every floor on one datum.

    1. Enquiry and constraints check

      We check the property against conservation areas, listed status, Article 4 directions, tree preservation orders, flood zone and planning history. We choose the right route and send a fixed quote.

    2. Measured survey

      We survey the house on one datum: rooms, levels, boundaries, drains, trees and the neighbours' windows that the 45° and 25° tests depend on.

    3. Design options

      We model the house in Revit and show you options in 3D and plan, with the planning strategy and the precedents in your street.

    4. Design frozen

      You choose an option in writing. Nothing changes after this without your say.

    5. Independent check

      A second chartered technologist checks every sheet against the council's validation checklist and the policy. A senior review signs it off before anything is submitted.

    6. Submission

      We prepare the forms, certificates, fee and documents and submit through the Planning Portal.

    7. Officer liaison

      We answer the planning officer and make any amendments within five working days, at no charge until approval.

    8. Building regulations

      Technical drawings are coordinated with the structural engineer's calculations, the drainage and the planning conditions.

    9. Approval and hand-over

      Building control approval, then a next-steps pack covering the commencement notice, party wall timing and CIL.

    Free redraws until approval. Every drawing set is checked independently, and the checker is never the person who drew it.

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    Converted loft bedroom with roof windows and a Juliet balcony

    The Hounslow rule that shapes an L-shaped dormer

    Hounslow's Residential Extension Guidelines SPD, in section 4.10, says that side and rear dormers must remain independent and must not wrap around to create one large extension. We cite it as the council's own wording on the point, and we have not found a numeric limit attached to it, so there is no figure to quote here.

    An L-shaped dormer is, by its nature, a rear dormer that turns a corner. Whether a given L reads as one wrapped extension or as two separate dormers that happen to meet is a question of the drawing: a clear break in the roof plane, different ridge or cheek heights, and a set-back at the corner can all show independence. We test those options on the model and show them as separate elevations.

    Where the roof of the house makes a true break impossible, we say so early. The honest answer may be one straight dormer now, or an application that argues the case with the drawings behind it.

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

    Local figures for Hounslow

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Householder decisions689 decisions1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Householder applications granted78.5 %1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Householder applications decided in time97.8 % decided within 8 weeks or an agreed extended period1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Conservation areas33 named conservation areas published by the council—planning.data.gov.uk
    Article 4 directions3 Article 4 directions published by the council—planning.data.gov.uk
    Listed building entries519 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    worldHeritageSites1 World Heritage Sites intersecting the LPA boundary—planning.data.gov.uk
    Green Belt share of the council area22 % of council area covered by green-belt polygons—planning.data.gov.uk
    Domestic gardens share of land (GLUD 2005)21.5 % of land that is domestic garden (GLUD 2005)2005data.london.gov.uk
    Mayoral CIL rate (indexed)72.73 £/m² (indexed, permissions granted in 2026)—london.gov.uk

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

    Councils bordering Hounslow

    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.Source: GLA Planning London Datahub, householder applications, all years held. Contains public sector information licensed under the Open Government Licence v3.0. Contains OS data © Crown copyright and database right 2026.
    Loft enlargement in section: the permitted development limitsExtra roof volume allowed: 40 m³ (terrace house) / 50 m³ (any other house) additional roof volume. Set-back from the eaves: Original eaves maintained; enlargement set at least 0.2 m from the eaves measured up the roof slope, so far as practicable (not required for hip-to-gable or roofs joining a rear/side extension). Height limit: No part higher than the highest part of the existing roofABC

    Loft enlargement in section: the permitted development limits

    A dormer on the rear slope, with the limits that decide whether it needs planning permission.

    A · Extra roof volume allowed
    40 m³ (terrace house) / 50 m³ (any other house) additional roof volume
    B · Set-back from the eaves
    Original eaves maintained; enlargement set at least 0.2 m from the eaves measured up the roof slope, so far as practicable (not required for hip-to-gable or roofs joining a rear/side extension)
    C · Height limit
    No part higher than the highest part of the existing roof

    A borough that refuses more than most

    The council decided 689 householder applications in its latest year and granted 78.5%, with 97.8% decided within eight weeks or an agreed extension. That leaves a real share of cases not granted, so presentation matters more here than the bare figures suggest.

    We use that as a reason to over-prepare, not to predict, and we say plainly if an L looks unlikely to pass. Each application carries a design and access note, elevations at the junction of the roofs and a sketch of the view from neighbouring gardens. If an officer has a question, the answer is already on the sheet.

    Timing is steady: the on-time figure suggests a case is decided close to the statutory period, so a complete first submission is the best way to avoid a second round of questions. Our planning drawings in Hounslow page lists the sheets we issue.

    Conservation areas, Article 4 and a World Heritage Site

    Hounslow has 33 conservation areas and 3 published Article 4 directions. Inside a conservation area a roof enlargement is not permitted development, so most L-shaped dormers there need an application.

    The council area also takes in 1 World Heritage Site. It will not decide the roof on an ordinary suburban street, but we check whether the address falls within its setting before we promise a route.

    Historic England lists 519 entries within the borough boundary. A listed house needs consent we do not draw on this site, and we tell you at the start if that is your case.

    Gardens, levy and trees

    Green Belt covers 22% of the council area. Houses on the borough edge may sit near it, and a roof extension adds no footprint, but the history of earlier building counts towards what the council will accept.

    The Mayor of London levy for permissions granted this year is 72.73 pounds per square metre. Any borough levy is read from the council charging schedule for the address. A conversion inside the existing envelope usually adds no chargeable area; if the drawings do, we tell you before you instruct a builder.

    Domestic gardens make up 21.5% of the borough's land, according to the national land-use database. That is a reminder that most Hounslow roofs are overlooked by many back gardens, which is exactly the view officers consider.

    Next steps for a Hounslow roof

    We survey the roof, draw the existing and proposed floor plans, the section through the dormer and all elevations, and work the volume out against the national allowance before you see a design. If a straight dormer solves the problem, dormer loft conversion drawings in Hounslow cover it, and the general loft conversion drawings in Hounslow page explains the stair and fire requirements.

    For the borough as a whole see architectural drawings in Hounslow, or compare the same service in neighbouring Richmond upon Thames.

    What you receive

    Planning drawing sheet for a rear extension with plans, elevations and sections
    Sample drawing. Planning drawings for a rear extension: plans, elevations and sections on one sheet set.
    Rear view of brick terraced houses in London with slate roofs and chimney stacks along the shared roofline
    Storey by storey
    Move up and down — the car travels between floors.

    Other services in Hounslow

    L-shaped dormer drawings nearby

    Questions

    Can I build an L-shaped dormer in Hounslow?

    It can be allowed, but Hounslow's guidance says side and rear dormers should remain independent and not wrap into one large extension. The drawings need to show the roof reading as separate pieces.

    What share of Hounslow householder applications are granted?

    78.5% of householder decisions were granted in the latest year. We treat it as a reason to prepare carefully, not as a forecast.

    Is a Hounslow conservation area dormer permitted development?

    No. With 33 conservation areas in the borough, we check whether your address is in one before suggesting a route.

    Sources and dates

    City of London skyline glowing at dusk across the Thames under a dramatic orange sky

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