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Harrow, London

Rear extension drawings in Harrow

Harrow lets you trade extra depth for distance from your neighbour. Our rear extension drawings for Harrow houses start at £695 including VAT, and the first job on every survey is working out how much depth your plot can afford under the council's two for one rule.

From £695 (VAT included)

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  • Fixed fees, VAT included

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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 rear 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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    Brick house being extended, with a wide new opening supported over the ground floor

    How Harrow's design guide measures a rear extension

    The Residential Design Guide treats permitted development depth as its reference point for a single-storey rear extension, with 4 m detached; 3 m semi/terraced, then adds the site and the effect on neighbours. A scheme that matches the norm starts from a settled position.

    Extra depth is where the guide gets distinctive. Anything beyond the norm has to be set in from the side boundaries by twice the additional depth, which the guide expresses as 2:1 set-in. A deeper extension is therefore negotiable, but it has to step away from the fence, and the plan must show that.

    Height is controlled on shared boundaries as well: 3 m flat; 3.5 m pitched mid-point. Roof balconies on extensions near a flank boundary are normally unacceptable, and flat roofs are usually conditioned against use as a terrace.

    The method that follows is straightforward. Choose the depth you want, work out the set-back it demands, then test the boundary height. If the figures will not close, we change the shape of the extension instead of straining the argument.

    Finished white-rendered rear house extension with large glazed doors

    Local figures for Harrow

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Where permission is needed, single-storey rear extension depth is judged for consistency with permitted development (4 metres detached; 3 metres semi-detached or terraced) plus site and neighbour impact.4 m detached; 3 m semi/terraced—harrow.gov.uk, Residential Design Guide SPD 2010, p.46, para 6.59
    Any extra depth beyond the norm must be set away from the side boundaries by twice the extra depth sought (the 'two for one' rule).2:1 set-in—harrow.gov.uk, Residential Design Guide SPD 2010, p.47, paras 6.60-6.61
    Single-storey rear extensions on a neighbouring boundary should be no more than 3 metres high with a flat roof, or 3.5 metres at the mid-point of a pitched roof.3 m flat; 3.5 m pitched mid-point—harrow.gov.uk, Residential Design Guide SPD 2010, p.47, para 6.63
    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
    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
    GPDO 2015 Sch 2 Pt 1 Class A, para A.1(f)(i)3 m (attached) / 4 m (detached) beyond the original rear wall, single storey—legislation.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

    Working the two for one arithmetic on a real plot

    The rule favours wide plots, because a wide plot has room to step the extension in from both sides. We run the arithmetic on the survey before you commit to a depth, so you see what each extra metre costs in set-back and in lost garden.

    The proposed plan is dimensioned from the original rear wall to the new one and from the new one to each boundary, which lets the officer check the rule without a scale rule. The same sheet records the wall height and roof pitch.

    Gardens matter too. Domestic gardens cover 34.7 per cent of Harrow's land in the Greater London Authority's land-use data, and we show how much of your own garden stays green after the build.

    Junctions with the old house get the same attention. A rear bay, a side passage or a chimney stack where the new wall must tie in changes both structure and elevation, so we record each one on the survey and draw the proposal over the real condition.

    Permission routes for a Harrow rear extension

    A single-storey extension within the national limits may be permitted development, and a longer one can use prior approval. Harrow's record on the longer route is lopsided: 27 larger home extension prior approvals were granted and 108 refused in the latest return. For that reason we often advise a householder application with a tailored design instead.

    The borough has 31 conservation areas, where the larger route is unavailable, and Historic England lists 295 entries. Green belt polygons cover 22 per cent of the area, and a house inside them faces tougher tests.

    The council's householder fee is £548, paid to it apart from our fixed fee. Building regulations are a separate approval; our building regulations drawings cover steel over the opening, insulation and drainage once the design is settled.

    Harrow's householder decisions

    Harrow decided 917 householder applications in its latest published year and granted 81.7 per cent, with 93.7 per cent decided in time.

    Those numbers describe the whole borough and predict nothing about one house. Where an officer asks for amendments, we revise and resubmit, usually after a short conversation with you about which measure to give way on.

    What you receive and what it costs

    A Harrow set holds existing and proposed plans, elevations and sections, with a location plan and a block plan. We charge £695 including VAT, agreed before work begins. A second chartered architectural technologist checks each sheet, and we redraw free of charge if the council asks for changes.

    For the wider picture, see architectural drawings in Harrow or the general guide to rear extension drawings across London. If a loft is also on your list, loft conversion drawings in Harrow can share the same survey.

    Related drawings and neighbouring boroughs

    Planning to fill the side as well? Read about wraparound extension drawings in Harrow, or compare every shape in house extension drawings for Harrow.

    Next door the guidance reads differently in Brent, Hillingdon and Ealing.

    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.
    Two-storey rear extension under construction on a semi-detached house
    Every side considered
    Flick across the turntable to spin it.

    Other services in Harrow

    Rear extension drawings nearby

    Questions

    What is Harrow's two for one rule?

    Any depth beyond the norm must be set away from the side boundaries by twice the extra depth sought: 2:1 set-in.

    How high can a rear extension be on the boundary in Harrow?

    The design guide gives 3 m flat; 3.5 m pitched mid-point for single-storey extensions on a neighbouring boundary.

    How much do rear extension drawings cost in Harrow?

    From £695 including VAT, agreed before work begins.

    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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