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Harrow, London

Retrospective planning application in Harrow

Built an extension in Harrow that the council later said needed permission? A retrospective planning application is the route to regularise it. Harrow granted 81.7 per cent of 917 householder decisions in its latest year, and the way it handled larger home extensions tells you a lot about where owners go wrong. Fixed quote after a free constraints check.

Fixed quote after a free constraints check

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We use it to check conservation areas and constraints.
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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 retrospective planning applications

    Seven 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.

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

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    Georgian brick terrace with sash windows, arched fanlight doorways, stone steps and iron railings in London

    The Harrow guidance your as-built extension is judged against

    The borough measures householder work against the Residential Design Guide SPD and its Harrow Local Plan 2021-2041, which the council adopted in 2,026. A retrospective application gets no softer reading than a new one: the officer asks whether the building you have is acceptable on the street it sits in.

    The Residential Design Guide is concerned with how additions relate to the original house, so our drawings are built around that relationship. We draw the original house and the addition in different line weights, dimension the depth, height and the gap to each side boundary, and show the roof junction in section, because those are the points an officer measures first.

    A large share of Harrow is suburban, with 65.4 per cent of households living in a house or bungalow and 58.8 per cent owning their home. Where a pair of houses has been extended at different times, we draw both halves so the officer can compare them.

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

    Local figures for Harrow

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Conservation areas31 named conservation areas published by the council—planning.data.gov.uk
    Green Belt share of the council area22 % of council area covered by green-belt polygons—planning.data.gov.uk
    Listed building entries295 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    Households living in a house65.4 % of households living in a house or bungalow (detached, semi-detached or terraced)Census 2021nomisweb.co.uk
    Householder decisions917 decisions1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Householder applications granted81.7 %1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Householder applications decided in time93.7 % decided within 8 weeks or an agreed extended period1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Larger home extension prior approvals granted27 decisions2025 Q2 to 2026 Q1 (1 Apr 2025 to 31 Mar 2026)assets.publishing.service.gov.uk
    Larger home extension prior approvals refused108 decisions2025 Q2 to 2026 Q1 (1 Apr 2025 to 31 Mar 2026)assets.publishing.service.gov.uk
    Lawful development certificate applications (PS1)461 certificates2025 Q2 to 2026 Q1 (1 Apr 2025 to 31 Mar 2026)assets.publishing.service.gov.uk
    TCPA 1990 s171B(1)-(3) as substituted by LURA 2023 s115, in force 25 Apr 202410 years—legislation.gov.uk
    Householder: alterations/extensions to a single dwellinghouse, from 1 Apr 2026548 GBP—ribblevalley.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 Harrow
    Which application your project needsLawful Development Certificate decision: 8 weeks. Prior approval decision: 42 days. Householder decision: 8 weeksYour projectWithin permitted development?Lawful Development CertificatePrior approvalHouseholder applicationYesLarger rear extensionNoABC

    Which application your project needs

    The usual route for a house; flats and listed buildings follow other rules.

    A · Lawful Development Certificate decision
    8 weeks
    B · Prior approval decision
    42 days
    C · Householder decision
    8 weeks

    Where larger extensions went wrong in Harrow

    Many owners build a deep single-storey rear extension believing it is permitted development. The larger home extension route needs a prior approval application, and neighbour objections are what the council weighs. In its latest figures Harrow granted 27 and refused 108 of those prior approvals.

    A refusal on that route, or no application at all, leaves a finished extension without cover. If that describes your house, a full retrospective application with proper drawings is usually the next step, and our prior approval drawings in Harrow show how the earlier route would have been drawn.

    The ratio is not a verdict on your case. It is a reminder that neighbour impact decides these applications, so we record the relationship to the adjoining windows precisely.

    Green Belt, conservation areas and listed buildings

    Roughly 22 per cent of the borough is Green Belt. Additions to a house there are judged against openness, which is stricter than the rest of Harrow, and an as-built extension that doubled the original footprint is a hard case to argue.

    Harrow also has 31 conservation areas, 295 listed building entries and 9 scheduled monuments touching the borough. We check each designation during the free constraints check, so you know the weight of the case before you commit to a fee.

    Timing, fees and the enforcement clock

    Householder cases moved quickly here: 93.7 per cent were decided within 8 weeks or an agreed extension. The statutory period for a non-major case is 8 weeks, and the application fee is £548.

    Enforcement is limited by time, and for most operational development the period is 10 years from completion. Do not treat that as a reason to wait, because lenders and buyers ask questions long before the clock expires.

    Added floorspace can attract levy too. Harrow charges £196.43/m² (Residential, Use Class C3, borough-wide), and the mayoral charge adds £60 per square metre at its base rate. We flag the likely liability in writing so there is no surprise later.

    First steps if the council has written to you

    A letter from Harrow about your extension is not the end of the road, but it does set a clock. Read it for a date, a named breach and any request to stop work or reduce the building. Do not ignore it, and do not start altering the structure before you have taken advice, because a partial demolition can leave the house in a worse position than the original.

    Send us the letter with your address. Within the free constraints check we tell you whether an application is open to you, whether a lawful development certificate is plausible, and whether the better move is to alter the building first. Sometimes a modest change, such as lowering a roof or moving a window, can give the officer a scheme to support.

    What we send and how it is priced

    You receive a measured as-built survey, existing and proposed plans, elevations and sections, the location plan and block plan, and a short note on how the scheme meets the guidance. Our planning drawings in Harrow use the same set, and each sheet is checked by a second chartered technologist.

    The price is a fixed quote after the constraints check. If the council asks for revisions we redraw them at no extra charge. Read more in architectural drawings in Harrow or the main retrospective planning service page. Nearby: Brent and Hillingdon.

    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
    The street around you
    Move across the plinth — the blocks rise around the pointer.

    Other services in Harrow

    Retrospective planning applications nearby

    Questions

    My rear extension was refused prior approval in Harrow. Can I still apply?

    Yes. A refused prior approval does not stop a full planning application, which the council then judges against its own design policies. Harrow refused 108 larger home extension prior approvals in its latest figures, so you are not alone.

    Does Green Belt affect an extension I have already built?

    It can. About 22 per cent of Harrow is Green Belt, and there additions are weighed against openness, so we check your address before quoting.

    How long does Harrow take to decide?

    The target is 8 weeks for a non-major case, and 93.7 per cent of householder cases met the deadline or an agreed extension.

    Could I be asked to remove the extension?

    Enforcement is possible until the time limit of 10 years runs out, which is why we advise regularising early. We cannot promise an outcome.

    Sources and dates

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

    Tell us about your property.

    We check the constraints, then send a fixed fee. Messages before 3pm get a reply the same working day.

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