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Harrow, London

Wraparound extension drawings in Harrow

Wraparound extension drawings in Harrow often concern semi-detached houses, and Harrow decided a lot of householder applications, 917 in the latest twelve months, with 81.7% granted. Our MCIAT chartered architectural technologists draw them from £1,195 including VAT, working to the Residential Design Guide SPD.

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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 wraparound extension 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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    Finished white-rendered rear house extension with large glazed doors

    Harrow, semis and the side extension rule

    Two-thirds of the borough's households, 65.4%, live in a house or bungalow, and 58.8% own their home. Many of those houses are semi-detached or detached with a driveway or garage at the side, which suits a wraparound well: the garage becomes the side arm and the rear room joins it.

    The national rule for the side arm is strict, single storey and no wider than half the original house, and the rear arm has its own depth limit. Because Harrow houses often have the garage built early, we measure what is original and what was added later. An earlier flat-roofed garage counts against the allowance in ways owners rarely expect.

    The council's own yardstick is the Residential Design Guide SPD, and we draw to it so the extension reads as part of the house. Where the street has a rhythm of gaps between pairs, the drawings show the gap kept.

    Two-storey rear extension under construction on a semi-detached house

    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
    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
    Households living in a house65.4 % of households living in a house or bungalow (detached, semi-detached or terraced)Census 2021nomisweb.co.uk
    Domestic gardens share of land (GLUD 2005)34.7 % of land that is domestic garden (GLUD 2005)2005data.london.gov.uk
    Supplementary planning documentResidential Design Guide SPD2010harrow.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
    Class A, para A.1(j)Side extension: single storey, max 4 m high, max half the width of the original house—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

    Householder applications by street in Harrow

    Streets in Harrow with the most householder applications, and the share approved
    StreetApplicationsApproved
    Headstone Lane3179%
    Norman Crescent2878%
    Albury Drive2675%
    Suffolk Road2576%
    Howberry Road2496%
    Evelyn Drive2284%
    Moss Lane2263%
    Whitchurch Gardens2288%
    Cannonbury Avenue2190%
    Kings Road2153%
    Sylvia Avenue2195%
    Cannon Lane2084%
    Alicia Gardens1988%
    South View Road1961%
    Christchurch Avenue1860%
    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.
    Single-storey rear extension: the permitted development limitsDepth beyond the original rear wall: 3 m (attached) / 4 m (detached) beyond the original rear wall, single storey. Maximum height: 4 m. Within the zone near the boundary: Eaves no higher than 3 m where within 2 m of the curtilage boundary. Larger extension under prior approval: 6 m (attached) / 8 m (detached), single storey, height max 4 m; not on article 2(3) land or an SSSIABCD

    Single-storey rear extension: the permitted development limits

    The house in section with a rear extension; the dashed lines mark the zone near the boundary.

    A · Depth beyond the original rear wall
    3 m (attached) / 4 m (detached) beyond the original rear wall, single storey
    B · Maximum height
    4 m
    C · Within the zone near the boundary
    Eaves no higher than 3 m where within 2 m of the curtilage boundary
    D · Larger extension under prior approval
    6 m (attached) / 8 m (detached), single storey, height max 4 m; not on article 2(3) land or an SSSI

    Green Belt, heritage and the edges of the borough

    About 22% of the borough's area falls under Green Belt polygons, and the borough has 31 conservation areas and 295 list entries. Homes at the northern edge or inside a conservation area face a stricter reading, and a wraparound with its side element cannot use the national permitted development rights in a conservation area at all.

    In the Green Belt an extension is judged by whether it is proportionate to the original house, so earlier additions matter. We total the existing and proposed floor area against the original and state the percentage change in the design statement.

    Harrow also adopted a new local plan, Harrow Local Plan 2021-2041, in 2,026, so the policy layer above the older design guide has changed recently. We read both before drawing.

    What the Harrow figures say about prior approval

    Harrow's figures show a stark split. In the latest return year the council granted 27 larger home extension prior approvals and refused 108. The route lets adjoining neighbours object, and the council then judges the effect on their amenity, so one objection can decide the outcome.

    For a wraparound that tells you something useful. Even where a deep rear extension looks permitted on paper, a neighbour's objection can end it, so a full householder application, at £548, often gives a firmer footing and the chance to explain the design. We discuss which route fits your plot before you commit to either.

    Domestic gardens make up 34.7% of the land here, a large share, so the garden left behind is a central part of the case.

    Roof and detail choices on a Harrow semi

    A semi-detached pair is read as a composition, so what you do on your half is judged against the other half. The roof is the main decision. A single-storey wraparound with a flat roof and a roof lantern keeps well below the first-floor windows and rarely troubles anyone, while a pitched roof tying into the main slope has to match the pitch and the tile exactly, or it looks like an afterthought.

    The side arm also removes the passage to the garden. We show a replacement route, whether through the new kitchen or through a retained gate, and we check that escape from the rear rooms still works for building control. Bins and cycles need a new home, and a small store tucked into the plan is better than an objection on the elevation.

    We draw each of these decisions explicitly, so the case officer sees a considered scheme.

    Drawings, certificates and the neighbours

    The set includes existing and proposed plans, elevations, sections and a roof plan, with a location plan and a block plan. If the scheme is within the permitted limits we can instead apply for a Lawful Development Certificate; Harrow handled 461 such applications in its latest return year, a high number that shows how common the route is here.

    Compare with the simpler options in rear extension drawings in Harrow or side return extension drawings in Harrow. Neighbours on both sides usually need party wall notices, and the planning register is searchable on the council's site.

    For the rest of our work in the borough, see architectural drawings in Harrow. We redraw free of charge if the council asks for changes before it decides.

    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.
    House extension under construction with scaffolding, new glazed doors and building materials
    Every side considered
    Flick across the turntable to spin it.

    Other services in Harrow

    Wraparound extension drawings nearby

    Questions

    Which Harrow guidance applies to extensions?

    The Residential Design Guide SPD, with the new plan, Harrow Local Plan 2021-2041.

    Does Green Belt stop a wraparound in Harrow?

    Not automatically. About 22% of the borough is Green Belt, and extensions there are judged on whether they are proportionate to the original house.

    Why does Harrow refuse so many prior approvals?

    The council refused 108 larger home extension prior approvals against 27 granted in the latest year. That route turns on the effect on adjoining neighbours.

    Will a flat roof or a pitched roof suit a Harrow semi?

    Either can work. A flat roof with a lantern stays low and avoids matching issues, while a pitched roof must match the existing pitch and tiles exactly.

    How much do the drawings cost?

    From £1,195 including VAT, plus the council's £548 application fee.

    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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