020 7864 7245Request a fixed quote

Hillingdon, London

Flat conversion drawings in Hillingdon

Hillingdon will only convert a house into flats if it is large enough, the street is not already full of flats, and each floor holds one unit. We prepare flat conversion drawings in Hillingdon from £1,195 including VAT, as MCIAT chartered architectural technologists, and we test your house against those three limits before any layout is drawn.

From £1,195 (VAT included)

  • 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 flat conversion drawings

    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.

    Request a fixed quote
    Pencil resting on a dimensioned technical drawing beside a scale rule

    Hillingdon's three limits on flat conversions

    The borough's Local Plan Part 2 sets out the test in a single development management policy. In summary it reads: 120 sqm; 10%; one unit per floor. The first figure is the internal floor area of the original building, the second is a cap on the share of flats along the street, and the last limits how many separate homes each storey may hold.

    Each limit is a check on facts, which is why we start with the survey and not a sketch. The floor area is measured on the original house, so a rear extension added later may not count towards it. The street share depends on how many neighbouring homes already have separate front doors, which means a short desk study of the road before we promise anything.

    The one-unit-per-floor limit shapes the entire layout. A three-storey terrace can be split vertically only in the ways that leave a single flat on each level, so we draw those options first and discard anything that breaks the rule. Where a scheme misses a limit, we say so in writing, in plain terms, before you commission further work. Our flat conversion drawings overview explains what a full set contains.

    Rear view of brick terraced houses in London with slate roofs and chimney stacks along the shared roofline

    Local figures for Hillingdon

    Figures with their unit, period and source
    MeasureValuePeriodSource
    Conversions to flats are only permitted where the original building's internal floor area is at least 120 sqm, the street would not exceed 10% flats, and units are limited to one per floor (Policy DMH 4).120 sqm; 10%; one unit per floor—hillingdon.gov.uk, Local Plan Part 2 DM Policies 2020, p.29, Policy DMH 4
    Minor application decisions367 decisions1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Minor applications granted68.7 %1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Minor applications decided in time89.4 % decided within 8 weeks or an agreed extended period1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Householder applications granted90.2 %1 July 2025 - 30 June 2026assets.publishing.service.gov.uk
    Green Belt share of the council area42 % of council area covered by green-belt polygons—planning.data.gov.uk
    Article 4 directions150 Article 4 directions published by the council—planning.data.gov.uk
    Tree preservation orders731 tree preservation orders published by the council—planning.data.gov.uk
    Mayoral CIL charging band2 MCIL2 charging band (1-3)—london.gov.uk
    Mayoral CIL rate (indexed)72.73 £/m² (indexed, permissions granted in 2026)—london.gov.uk
    Borough CIL residential rate£160.43/m² (Residential dwelling houses C3, borough-wide)2026 indexed rate as printed; schedule rate £95/m² (index 237 to 400)pre.hillingdon.gov.uk
    Change of use of a building to one or more separate dwellinghouses, not more than 10: per dwellinghouse, from 1 Apr 2026610 GBP per dwelling—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 Hillingdon
    Building regulations, layer by layerPart A: structure: Approved Document A: Structure, 2004 edition incorporating 2004, 2010 and 2013 amendments. Part B: fire safety: All dwellings: fire detection and alarm system minimum Grade D2 Category LD3 (BS 5839-6), mains-operated smoke alarms to BS EN 14604. Part L: insulation: New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4. Part K: stairs: 2.0 m clear headroom over stairs. Full plans application: Building control body must decide a full plans application within 5 weeks, or longer if agreed in writingPart A: structurePart B: fire safetyPart L: insulationPart K: stairsFull plans applicationABCDE

    Building regulations, layer by layer

    The Approved Documents that shape most house projects, from structure to the application itself.

    A · Part A: structure
    Approved Document A: Structure, 2004 edition incorporating 2004, 2010 and 2013 amendments
    B · Part B: fire safety
    All dwellings: fire detection and alarm system minimum Grade D2 Category LD3 (BS 5839-6), mains-operated smoke alarms to BS EN 14604
    C · Part L: insulation
    New elements in existing dwellings, limiting U-values W/(m²·K): roof 0.15, wall 0.18, floor 0.18, windows 1.4 (or WER Band B), doors 1.4
    D · Part K: stairs
    2.0 m clear headroom over stairs
    E · Full plans application
    Building control body must decide a full plans application within 5 weeks, or longer if agreed in writing

    How Hillingdon decides smaller schemes

    A conversion into two or three flats counts as a minor application. In the latest twelve months of published figures the council decided 367 minor applications and granted 68.7 per cent of them, with 89.4 per cent decided within eight weeks or an agreed extension.

    That grant rate is well below the 90.2 per cent the council grants for householder work such as extensions. The gap is the useful lesson. A flat conversion is judged on space, parking, amenity and the street, and those tests are more demanding than an extension's, so the drawings carry more weight.

    We therefore build the schedule of areas, the bin and cycle stores and the garden division into the first set rather than leaving them for the case officer to request. We also read the council's online planning register for conversions already decided on your road, which tells us how officers have applied the rule locally.

    Green Belt, directions and trees in a borough this large

    Green Belt covers 42 per cent of Hillingdon. A conversion happens inside the existing walls, but any extension you add to make a flat work is tested against Green Belt policy, so we keep added bulk to a minimum.

    The council also publishes 150 Article 4 directions, 33 conservation areas and 731 tree preservation orders. Any of these can alter the exterior changes a conversion usually needs: a second front door, a new window to a bedroom, a bin store at the frontage.

    We run a constraints check on the address as part of the survey stage, so you hear about a direction or protected tree before the layout depends on it. Our architectural drawings page for Hillingdon lists each of the borough's constraints in more detail.

    Space, sound and the costs that sit outside the drawings

    Every flat must meet the national space standard, and London adds its own height and outdoor-space rules. The London Plan asks for a floor-to-ceiling height of 2.5 m across most of each flat, which can rule out a cramped loft or a low ground floor.

    The Mayor's levy is charged on new floor area. Hillingdon sits in charging band 2, and for permissions granted this year the indexed rate is £72.73 per square metre. The council has its own residential rate as well, shown in the table below, and the usual exemption for small extensions does not apply where a new dwelling is created.

    The planning fee is £610 for each flat created, paid to the council. For comparison, the borough's average flat sells for around £285,116 against £457,686 for a terraced house, a spread you can weigh against build cost.

    What our Hillingdon set includes

    You receive existing and proposed floor plans for every level, elevations, sections, a block plan, a schedule of areas for each flat and a note on how each limit is met. Once planning is in hand we can move to building regulations drawings, and sold or let flats will each need lease plans.

    Neighbouring boroughs apply different tests, so if you own across the border see flat conversion drawings in Hounslow as a comparison.

    What you receive

    Building regulations section drawing showing the construction build-up
    Sample drawing. Building regulations section showing construction build-up for a building control check.
    Upper floors of a large yellow-brick Victorian house in London with chimney pots
    Unit by unit
    Move up and down — the nearest units slide out.

    Other services in Hillingdon

    Flat conversion drawings nearby

    Questions

    Can I convert my Hillingdon house into flats if it is a small semi?

    Usually not. The council's policy asks for a minimum original floor area, and smaller houses fall below it. We measure first and tell you before you pay for design.

    Does the street limit stop every conversion on a road with existing flats?

    It caps the share of flats on the street, so a road already near the limit may be closed to new conversions. We check the street as part of the desk study.

    How much does the council charge to apply for a conversion?

    The national fee is £610 for each flat created. Our fixed drawing price starts at £1,195 including VAT.

    Is Green Belt a barrier to converting a house into flats?

    A conversion is a change of use inside the existing building, so it is not barred by itself. Extensions you add to the house are tested against Green Belt rules.

    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