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Hillingdon, London

Double-storey extension drawings in Hillingdon

In Hillingdon the first floor of an extension is tested against your neighbour's window before anything else. Our double-storey extension drawings start at £1,295, and the plan, section and elevations show that test passing, so the case is clear to the planning officer.

From £1,295 (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 double-storey 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

    The Hillingdon policy for a two-storey extension

    Hillingdon's Local Plan Part 2 holds the rules in one place, the household development policy known as DMHD. For a two-storey extension the first test is a daylight line and a distance: 45 degrees; 21 metres. The line is taken from the centre of the nearest neighbouring window at ground or first floor, and the distance is the gap kept to windows that would otherwise look across at other houses.

    The policy also says what a first floor should not be. A flat roof is only acceptable when it suits the existing house, and a full-width two-storey rear extension is unacceptable on a listed or locally listed building and inside any designated area. A half-width scheme, stepped away from one boundary, is the shape this borough tends to support.

    For a side addition the measures are half width; 1 m set-in; 1 m set-back: no more than half the width of the original house, a set-in from the side boundary and a set-back from the front wall. We draw the set-in on the first-floor plan itself, because it is the dimension builders most often lose between approval and site.

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

    Local figures for Hillingdon

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Two-storey extensions must not cross a 45-degree line from the centre of the nearest neighbouring ground or first-floor habitable-room window, nor have windows overlooking other houses at less than 21 metres.45 degrees; 21 metres—hillingdon.gov.uk, Local Plan Part 2 DM Policies 2020, p.131, Policy DMHD 1 B(vi)
    Side extensions should not exceed half the width of the original house; two-storey side extensions must be set in at least 1 metre from the side boundary (1.5 metres in Copse Wood and Gatehill Estates) and set back at least 1 metre from the front.half width; 1 m set-in; 1 m set-back—hillingdon.gov.uk, Local Plan Part 2 DM Policies 2020, p.131, Policy DMHD 1 C(i), (iv)-(v)
    Article 4 directions150 Article 4 directions published by the council—planning.data.gov.uk
    Conservation areas33 named conservation areas published by the council—planning.data.gov.uk
    Tree preservation orders731 tree preservation orders published by the council—planning.data.gov.uk
    Green Belt share of the council area42 % of council area covered by green-belt polygons—planning.data.gov.uk
    Listed building entries436 list entries (Historic England, within the LPA boundary)—planning.data.gov.uk
    Householder applications granted90.2 %1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Householder applications decided in time94.3 % decided within 8 weeks or an agreed extended period1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Class A, para A.1(h)Over one storey: max 3 m beyond the original rear wall and not within 7 m of the rear boundary—legislation.gov.uk
    Class A, condition A.3(b); Class B, condition B.2(c)Upper-floor side windows obscure-glazed and non-opening below 1.7 m above floor—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 Hillingdon
    The 45-degree test in planTest used in daylight assessments: 45 degrees (plan and elevation)A

    The 45-degree test in plan

    A line from the middle of the neighbour's nearest window: the extension should stay behind it.

    A · Test used in daylight assessments
    45 degrees (plan and elevation)

    A borough of many designations

    Hillingdon publishes 150 Article 4 directions, and 33 conservation areas sit alongside 436 listed entries. Where a direction is in force, rights that normally let an owner build without an application can be switched off, so an address check is the first job on every Hillingdon enquiry.

    Trees add a second layer. The council has made 731 tree preservation orders, and a protected tree near a rear wall changes where foundations can go. The Green Belt covers 42 per cent of the borough and, where it applies, limits how large an extension can grow compared with the original house.

    In a conservation area the national rule is simple: No rear extension of more than one storey under PD on article 2(3) land. That rule removes the permitted development route and leaves a householder application.

    Permitted development for a second storey

    Away from designated land, the national limit for an upper-floor rear extension is strict: Over one storey: max 3 m beyond the original rear wall and not within 7 m of the rear boundary. On a house with a short garden that leaves almost nothing, and the application route is the practical one.

    Two conditions carry over whichever route is used. Side windows on the upper floor: Upper-floor side windows obscure-glazed and non-opening below 1.7 m above floor. The roof: Roof pitch of a 2+ storey enlargement to match the original house so far as practicable. Both go on the elevation notes so the builder sees them.

    Who is building up in Hillingdon

    Households in a house or bungalow make up 68.9 per cent of the borough and 56.6 per cent are owner-occupied. A semi-detached house averages £583,573 and a detached one £941,938 in the latest Land Registry figures. For the owner of a semi, that spread is the figure to weigh an extra floor against before deciding to move.

    Gardens occupy 18.6 per cent of the land in the borough according to the national land-use survey, so there is room, though the overlooking distance in the daylight-and-privacy rule usually decides how far a first-floor window can sit from the rear boundary.

    Decision record and timing

    Hillingdon decided 1,147 householder applications in its latest published year and granted 90.2 per cent. It met the eight-week deadline or an agreed extension in 94.3 per cent of cases. These are borough-wide figures for every kind of householder work, not a forecast for one house, but they are the reason we set aside a little margin before the builder's start date.

    What the Hillingdon set contains

    You receive existing and proposed floor plans for both storeys, sections through the new room and the boundary, all elevations with the neighbour's windows plotted, and the location and block plans. A second chartered technologist checks every sheet and we redraw free until approval if the council asks for amendments.

    If you would rather keep to one storey, see rear extension drawings in Hillingdon. Borough-wide constraints are on architectural drawings in Hillingdon. The same service is available just east in Hounslow and north in Harrow, and the generic explanation is at double-storey extension drawings.

    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 Hillingdon

    Double-storey extension drawings nearby

    Questions

    What is the daylight test for a two-storey extension in Hillingdon?

    The DMHD policy gives 45 degrees; 21 metres: an extension must not cross the daylight line drawn from the centre of the neighbour's nearest window, and windows should not look at other houses from closer than the stated distance.

    Can I build a full-width first floor at the back in Hillingdon?

    Not in a designated area or on a listed or locally listed building, where the policy treats it as unacceptable. Elsewhere it must suit the house and pass the daylight line, so a half-width scheme is often the safer route.

    Does an Article 4 direction stop me extending?

    It can remove the permitted development right, so you would apply for planning permission instead. Hillingdon has 150 directions, so we check your address before quoting.

    How much will the drawings cost?

    From £1,295, fixed up front. The council's application fee of £548 is separate.

    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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