The whole spectrum — rear extensions, side returns, wraparounds, double-storey, basement digs. Planning-led design with detailed technical phase, ideal for 1930s semi-detached dominates typical of Hillingdon.
Hillingdon decided 3,978 householder applications in the three years to March 2026 and approved 84.2%. On the 6m prior approval route it handled 476 notifications and told 354 of them that no prior approval was required. Its householder appeals also succeed often: 45.4% of 1,126, median 57 days.
| Measure | Hillingdon | Outcome |
|---|---|---|
| Householder decisions | 3,978 | 84.2% approved |
| Decided inside eight weeks | 93.0% | — |
| Larger-extension notifications | 476 | 354 not required, 77 granted, 45 refused |
| Lawful development certificates issued | 1,756 | — |
| Extension applications in the Datahub | 11,496 | 74% approved |
| Householder appeals decided | 1,126 | 45.4% allowed, median 57 days |
Sources: rows one to four from MHCLG District Planning Application Statistics (PS1 and PS2), decisions made in the twelve quarters to March 2026. Row five from the Planning London Datahub, retrieved 15 August 2026 — phrase-matched descriptions, comparable within Hillingdon only. Row six from Planning Inspectorate casework decided 2016–2026. Open Government Licence v3.0.
In Hillingdon — 1930s semi-detached dominates; Metropolitan Green Belt covers much of north Hillingdon; Victorian cottages in Uxbridge and Ruislip villages; post-war housing near Heathrow for the most part — a house extension drawings package is the full measured-survey-to-submission drawing set London Borough of Hillingdon needs in order to determine an application: existing and proposed plans, elevations and sections at 1:100 and 1:50, a location and site plan, and the supporting statements the case officer asks for.
Prepared and reviewed by the chartered technologist team at Architectural Drawings London — MCIAT chartered, £2m PI insured.Last reviewed 2026-08-03.
The whole spectrum — rear extensions, side returns, wraparounds, double-storey, basement digs. Planning-led design with detailed technical phase, ideal for 1930s semi-detached dominates typical of Hillingdon.
Housing stock in Hillingdon: 1930s semi-detached dominates; Metropolitan Green Belt covers much of north Hillingdon; Victorian cottages in Uxbridge and Ruislip villages; post-war housing near Heathrow.
Character: Largest outer west London borough; significant Green Belt; Heathrow noise contours affect planning decisions in Harmondsworth and Sipson.
Measured existing survey, photographic record, Article 4 and conservation check specific to Hillingdon before we quote.
2–3 design options at concept stage — alternative layouts, glazing, roof forms.
Site location plan, existing and proposed plans, elevations, sections, D&AS where required.
Steel beam, foundation, lintel design. Chartered engineer sign-off.
Party Wall notices where needed; Thames Water Build Over Agreement where within 3m of a public sewer.
Single planning or regs submission.
Planning + building regs + structural.
Listed, conservation, complex sites.
Move the controls for an indicative figure. It anchors your budget — it is not a quote. Every project is priced after a free survey.
Build costs are separate and quoted by your contractor. See our published fees.
Every Hillingdon postcode district we draw in, the stock that dominates it and the authority that validates a house extension there. Hillingdon fees below are the statutory England rates for 2026, not house extension estimates.
| Postcode | Area | Dominant stock | What it means for a house extension |
|---|---|---|---|
| HA6 | Northwood | 1930s detached, Edwardian villas | A house extension at an HA6 address in Northwood is determined by Hillingdon Council under its own Local Plan policies for Northwood. |
| UB3 | Hayes / Harlington | 1930s semi-detached, post-war estates | UB3 covers Hayes / Harlington only; Hillingdon Council handles the house extension, and Hayes / Harlington case officers apply the UB3 conservation-area map. |
| UB4 | Hayes / Yeading | 1930s semi-detached, post-war estates | A house extension at an UB4 address in Hayes / Yeading is determined by Hillingdon Council under its own Local Plan policies for Hayes / Yeading. |
| UB7 | West Drayton / Sipson / Harmondsworth | 1930s semi-detached, post-war | West Drayton / Sipson / Harmondsworth sits wholly inside UB7, so Hillingdon Council validates every house extension submitted from an UB7 address. |
| UB8 | Uxbridge / Cowley | Georgian fragments, 1930s semi-detached, post-war flats | UB8 covers Uxbridge / Cowley only; Hillingdon Council handles the house extension, and Uxbridge / Cowley case officers apply the UB8 conservation-area map. |
| UB9 | Denham / Harefield | Tudor and Georgian fragments, 1930s semi-detached | A house extension at an UB9 address in Denham / Harefield is determined by Hillingdon Council under its own Local Plan policies for Denham / Harefield. |
| UB10 | Hillingdon / Ickenham | 1930s semi-detached, Tudor fragments | Hillingdon / Ickenham sits wholly inside UB10, so Hillingdon Council validates every house extension submitted from an UB10 address. |
| UB11 | Stockley Park | 1930s semi-detached dominates; Metropolitan Green Belt covers much of north Hillingdon; Victorian cottages in Uxbridge and Ruislip villages; post-war housing near Heathrow | A house extension at an UB11 address in Stockley Park is determined by Hillingdon Council under its own Local Plan policies for Stockley Park. |
Roof pitch, wall build-up and plot depth change every few Hillingdon streets, and each one changes what a house extension can achieve at that address.
Conservation areas covering Hillingdon: Hillingdon Council runs 29, and Ruislip Village, Northwood, Harefield are the ones Hillingdon owners meet most. A house extension inside a Hillingdon conservation area loses permitted development, so the Hillingdon submission is a householder application at £548 decided in 8 weeks — not a £249 prior approval decided in 6 weeks. In Harefield a house extension is judged on the street elevation first.
No blanket Article 4 over Hillingdon: Hillingdon Council has not withdrawn permitted development across Hillingdon, so a house extension outside a Hillingdon conservation area usually keeps it. The £274 Lawful Development Certificate is still the document a HA4 owner wants on file.
The building fabric around Hillingdon: 1930s semi-detached dominates; Metropolitan Green Belt covers much of north Hillingdon; Victorian cottages in Uxbridge and Ruislip villages; post-war housing near Heathrow. Largest outer west London borough; significant Green Belt; Heathrow noise contours affect planning decisions in Harmondsworth and Sipson. A house extension in Hillingdon is scoped against that stock first, because it decides whether the scheme runs as permitted development, a £274 Lawful Development Certificate, or a full £548 application to Hillingdon Council.
Sources for this Hillingdon house extension page: borough policies maps and conservation-area registers (2025–26), Royal Mail postcode district boundaries, the Town and Country Planning (Fees for Applications) (England) Regulations, the Town and Country Planning (General Permitted Development) (England) Order 2015 as amended, and the Party Wall etc. Act 1996.
Of 1,126 householder appeals decided in Hillingdon over the window covering appeals decided 2016-2026, an appeal against Hillingdon succeeded more often than the London norm — 45.4% against 39.0% city-wide. 511 were allowed and 588 dismissed, with 27 split. Extensions and other alterations to a single home are decided as householder applications, so these 1,126 cases are the population a refusal in Hillingdon joins on appeal - not the far larger number that were simply approved.
Half of those Hillingdon appeals took more than 57 days to decide from the day the appeal started — time added on top of the council's own determination period, which is the argument for getting the application right first. 100.0% were decided by written representations rather than a hearing or inquiry, meaning the written case and the drawings were the whole of the evidence.
1,126 householder appeals decided in Hillingdon. Source: Planning Inspectorate casework, OGL v3.0.
Direct answers to the questions Hillingdon homeowners ask every week about house extension drawings.
Start a free quote →Most standard extensions in Hillingdon qualify as Permitted Development — single-storey rear up to 3m/4m, side extensions up to half the width of the house, under standard national rules. Flats, listed buildings and conservation areas need full planning permission. We confirm eligibility at the free site survey.
Standard permitted development allows single-storey rear extensions up to 3m (attached house) or 4m (detached) in Hillingdon. Larger extensions up to 6m/8m are allowed under Prior Approval (Class AA). Flats, listed buildings and Article 4 areas in Hillingdon are excluded from these PD rights.
A Hillingdon extension has two cost lines: our architectural package (planning, building regulations and structural calculations in one fixed quote) and the build itself, which contractors price per square metre and which moves with access, ground conditions and specification. A side return typically costs less per m² than a double-storey rear. See our fees.
Hillingdon does not have a borough-specific basement policy beyond the national framework — basement conversions are generally permissible subject to structural, drainage and flood-risk considerations. Thames Water Build Over Agreements apply where you're within 3m of a public sewer.
Most Victorian terraces in Hillingdon (particularly in Uxbridge) benefit from both — a side return extension infills the narrow side passage to create a wider kitchen, a rear extension projects back into the garden. A wraparound combines the two. We recommend the best option at the free site visit.
Hillingdon's 1930s semi-detached dominates terraced and semi-detached stock typically suits rear single-storey extensions (kitchen-diners), side-return infill extensions, or double-storey rear. Wraparound extensions combine both directions for maximum gain. We recommend the most viable option at the free site visit.
We cover all Hillingdon postcodes — HA4, HA5, HA6, UB3, UB4, UB7, UB8, UB9, UB10, UB11 — with local surveyors. Survey appointments within 3 working days.
Hillingdon Council follows the London Plan and its own Local Development Framework. Extensions must match or complement existing materials, respect neighbour amenity and comply with Part L. We include a Pre-Application Advice summary where the planning history is complex.
If your property sits on a boundary, here are the neighbouring options.
We cover every architectural technology service in Hillingdon with one chartered team.
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Hillingdon's most space-efficient loft solution when PD-route dormers are blocked. Our chartered team designs mansards that get approved in ...
Turn your unused Hillingdon garage into a bedroom, home office or open-plan kitchen-diner. Planning route assessment, full building regulati...
Full architectural technology service for basement digs and cellar conversions in Hillingdon — structural underpinning design, waterproofing...
Chartered structural engineer calculations for every residential intervention in Hillingdon — steel beams, lintels, pad foundations, wall re...
Measured surveys across Hillingdon — floor plans, elevations and sections to ±3mm accuracy. Leica Disto laser + BLK360 point-cloud scanning,...
End-to-end Party Wall Act 1996 service for Hillingdon — Section 1, 3 and 6 notices, schedule of condition surveys, party wall award coordina...
London's most popular loft type — the full-width rear dormer. Planning or Permitted Development route assessed for your Hillingdon property,...
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