020 7864 7245Request a fixed quote

Hillingdon, London

L-shaped dormer drawings in Hillingdon

L-shaped dormer drawings in Hillingdon start with the map, not the roof. The borough publishes 150 Article 4 directions and 33 conservation areas, so whether an L-shaped dormer is permitted development depends on which street the house stands on.

Fixed quote after a free constraints check

  • MCIAT chartered
  • £2m PI insured
  • LABC Partnered
  • Fixed fees, VAT included

Request a fixed quote

We use it to check conservation areas and constraints.
Pick the council that decides your application.
A few lines: what you want to build, and anything the council has already said.
Add photos or drawings

Drop files here or choose from your device

PDF, JPG, PNG, DWG · up to 10 files, 90 MB in total

    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.

    Request a fixed quote
    Slate-clad roof extension on a yellow-brick London terraced house

    Article 4 land and conservation areas in Hillingdon

    An Article 4 direction removes a permitted development right in a defined area. Hillingdon has published 150 of them, and each one covers its own set of rights, so one house may lose its dormer right while the house two streets away keeps it. That makes the council map the first thing we open, and we read each direction that touches the property rather than assume.

    Conservation areas are the stronger filter for roofs. The borough has 33, and inside one a roof enlargement is not permitted development at all. Add 436 Historic England list entries and the practical answer for many addresses is a planning application, drawn to show how the dormer sits against the roof and the neighbouring gardens.

    We give you the finding in plain terms before any design fee is committed: permitted development, a lawful development certificate, or householder planning. Where it is planning, our planning drawings in Hillingdon page sets out the sheets.

    Converted loft bedroom with roof windows and a Juliet balcony

    Local figures for Hillingdon

    Figures with their unit, period and source
    MeasureValuePeriodSource
    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
    Listed building entries436 list entries (Historic England, within the LPA boundary)—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
    Householder decisions1,147 decisions1 July 2025 - 30 June 2026assets.publishing.service.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
    Lawful development certificate applications (PS1)529 certificates2025 Q2 to 2026 Q1 (1 Apr 2025 to 31 Mar 2026)assets.publishing.service.gov.uk
    GPDO 2015 Sch 2 Pt 1 Class B, para B.1(d)40 m³ (terrace house) / 50 m³ (any other house) additional roof volume—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
    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

    Where an L-shaped dormer suits Hillingdon houses

    Hillingdon is mostly suburban, with 68.9% of households in a house or bungalow and 56.6% owner-occupiers. Where one of those houses has a rear wing, an L-shape earns its place: the dormer runs along the main roof and turns along the wing, so the stair can land in a proper hall and the second room has a normal door.

    A semi-detached house has the larger roof allowance under national rules, set at 40 m³ (terrace house) / 50 m³ (any other house) additional roof volume, but the allowance includes any previous roof work. We ask for the planning history and any old extension drawings, and measure the roof on survey day.

    We also look at what the L looks like from the garden of the next house. A flat-roofed box with a short return is easier to defend than a long one stepped back awkwardly, and the drawings show that elevation clearly so the council can see it.

    Trees, Green Belt and the edge of the borough

    Hillingdon publishes 731 tree preservation orders, which is a lot of protected trees to plan around. A roof extension rarely touches one, but scaffolding, a new stair or an extension to the wing sometimes does, and we check the trees on the plan before the builder arrives.

    Green Belt polygons cover 42% of the borough, and houses near its edge can sit in or near it. For a dormer, which adds no footprint, the Green Belt rules matter less than for an extension, but the history of the site can still count against the volume you add.

    For the levy, we check the Hillingdon charging schedule for the address, and the Mayor of London adds 72.73 pounds per square metre this year, but a roof conversion inside the existing envelope normally adds no chargeable floorspace. We say when the drawings change that.

    How Hillingdon decides householder cases

    In its latest year Hillingdon decided 1,147 householder applications and granted 90.2%. 94.3% were decided on time, meaning inside eight weeks or an agreed extension.

    A high grant rate means the borough is prepared to approve well-judged work, not that every roof is waved through. Applications that fail tend to fail on the detail, so the junction of the L and the setback from the neighbour carry most of our drawing effort.

    Alongside applications the council handled 529 lawful development certificates in the latest four quarters. Where your dormer qualifies as permitted development, a certificate gives you written proof for a future sale, and our lawful development certificate drawings in Hillingdon are prepared for it.

    Before you commit to the L

    Not every Hillingdon roof needs the full shape. Compare it with dormer loft conversion drawings in Hillingdon, and read the general loft conversion drawings in Hillingdon page for stair and fire rules. For the borough overview see architectural drawings in Hillingdon, or compare the same service across the border in 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.
    Brick cottage with a tiled roof, chimneys and a front dormer window
    Storey by storey
    Move up and down — the car travels between floors.

    Other services in Hillingdon

    L-shaped dormer drawings nearby

    Questions

    How do I know if an Article 4 direction affects my Hillingdon house?

    Hillingdon has published 150 directions, each covering different rights in a defined area. We check the council map against your address and read the direction before telling you the route.

    What share of Hillingdon householder applications are granted?

    The council granted 90.2% of its householder decisions in the latest year. That is a borough figure and does not predict the outcome for an individual roof.

    Can an L-shaped dormer be permitted development in Hillingdon?

    Sometimes. It has to be outside conservation areas and any Article 4 land, within the volume allowance and on a house that has not used the allowance already. We confirm this at the start.

    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.

    Request a fixed quoteCall 020 7864 7245WhatsApp