Side returns, wraparounds, two-storey rears and basement digs, in a borough of 111,270 dwellings — planning-led design carried into the technical package, on Chiswick's Edwardian villas as readily as on the interwar semis out at Feltham.
Harder than most. Hounslow approved 69.9% of the householder applications it decided in the three years to March 2026 — 1,615 of 2,310 — against 83.0% across London. Only Barking and Dagenham and Greenwich sit lower. Its Datahub set records 33,282 extension applications at 67% approved.
| Householder applications, three years to March 2026 | Hounslow | London |
|---|---|---|
| Approval rate | 69.9% | 83.0% |
| Decisions made | 2,310 | 77,680 |
| Refused | 695 | — |
| Decided inside eight weeks | 91.2% | — |
| Larger-extension notifications | 477 | 354 not required, 78 granted, 45 refused |
| Householder appeals allowed after refusal | 49.3% of 659 | 40.8% of 13,067 |
Sources: decision figures from MHCLG District Planning Application Statistics (PS1 and PS2), twelve quarters to March 2026; appeal figures from Planning Inspectorate casework decided 2016–2026. Open Government Licence v3.0, retrieved 1 September 2026. Hounslow’s appeal-allowed rate of 47.2% is among the highest in London, which is the clearest sign that a Hounslow refusal is worth reading twice before accepting.
In Hounslow — Edwardian villas in Chiswick and Turnham Green; Georgian in Isleworth; 1930s semi-detached in Hounslow and Feltham; riverside new-build in Brentford for the most part — a house extension drawings package is the full measured-survey-to-submission drawing set London Borough of Hounslow 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 architectural technologist team at Architectural Drawings London — CIAT Affiliate, professional indemnity 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 edwardian villas in Chiswick and Turnham Green typical of Hounslow.
Housing stock in Hounslow: Edwardian villas in Chiswick and Turnham Green; Georgian in Isleworth; 1930s semi-detached in Hounslow and Feltham; riverside new-build in Brentford.
Character: Chiswick is one of west London's most conservation-controlled areas; outer Hounslow is permissive suburban.
We laser-measure and photograph the house first, then test the address against Hounslow's Article 4 directions and its 30 conservation area boundaries. That happens before the fee is quoted, not after it.
Two or three concept layouts before anything is costed: where the glazing sits, whether the roof runs flat with rooflights or pitches back toward the existing ridge, and how far the plan can push into the garden without arguing with the neighbour's daylight.
The submitted set is a location plan, existing and proposed floor plans, every elevation the work touches, sections cut through the new structure, and a design and access statement wherever the borough's validation list asks for one.
Steel beam, foundation, lintel design. Chartered engineer sign-off.
Where a new steel bears into a wall you share with next door, that is section 2 work and the notice goes out under section 3 of the Party Wall etc. Act 1996, two months before anything starts. Digging near a neighbour's foundations is section 6, and needs one month. Thames Water requires a Build Over Agreement separately, wherever the footprint lands 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 site survey.
Build costs are separate and quoted by your contractor. See our published fees.
Every Hounslow district we work in, listed with its prevailing house type and the council that validates an extension at that address. TW covers most of the borough; W3 and W4 do not sit tidily inside it. Every charge shown below is a statutory England rate set for 2026 — none of it is our quote.
| Postcode | Area | Dominant stock | What it means for a house extension |
|---|---|---|---|
| TW4 | Hounslow West | Edwardian villas in Chiswick and Turnham Green; Georgian in Isleworth; 1930s semi-detached in Hounslow and Feltham; riverside new-build in Brentford | TW4 is Hounslow West alone. The district's conservation-area map is the first thing a case officer measures an extension drawing against. |
| TW5 | Heston / Cranford | Edwardian villas in Chiswick and Turnham Green; Georgian in Isleworth; 1930s semi-detached in Hounslow and Feltham; riverside new-build in Brentford | TW5 (Heston and Cranford) lies entirely within the borough, so an extension from any TW5 address is validated and decided by Hounslow Council. |
| TW7 | Isleworth | Georgian and Victorian terraces | Isleworth is TW7, where the Local Plan policies on riverside setting and the Old Isleworth character are applied to an extension proposal. |
| TW8 | Brentford | Georgian fragments, Victorian terraces, new-build | Brentford is TW8. Hounslow Council decides here, with the Great West Road regeneration policies sitting alongside the ordinary householder tests. |
| TW13 | Feltham | 1930s semi-detached, post-war estates | TW13 is Feltham proper — determined by Hounslow Council, on interwar and post-war suburban stock rather than on period terraces. |
| TW14 | Feltham / East Bedfont | Edwardian villas in Chiswick and Turnham Green; Georgian in Isleworth; 1930s semi-detached in Hounslow and Feltham; riverside new-build in Brentford | Feltham and East Bedfont share TW14 on the western edge of the borough, and Hounslow Council is the deciding authority for an extension at either. |
| W3 | Acton | Victorian and Edwardian terraces | W3 (Acton) is split. Most of it answers to Ealing, the southern edge to Hounslow, and the policies map settles an extension street by street rather than by postcode. |
| W4 | Chiswick / Bedford Park | Arts & Crafts villas (listed) | W4 takes in Chiswick and Bedford Park and does not respect the borough line: some addresses are Hounslow, others Ealing. Establish which one before W4 drawings go anywhere. |
Pitch, wall build-up and plot depth are nothing like constant between Chiswick and Cranford, and each one changes how much extension a particular address can actually carry.
Hounslow conservation designations: thirty of them, with Bedford Park, Old Isleworth and Brentford the ones owners meet most often. Inside a designation the permitted-development route closes, so the extension becomes a householder application at £548 on an eight-week target rather than a £249 prior approval at six weeks. Bedford Park is the designation that most often sends a Hounslow extension back for redesign.
No blanket Article 4 over Hounslow: Hounslow Council has not withdrawn permitted development across Hounslow, so a house extension outside a Hounslow conservation area usually keeps it. The £274 Lawful Development Certificate is still the document a W4 owner wants on file.
Hounslow housing stock: Edwardian villas in Chiswick and Turnham Green; Georgian in Isleworth; 1930s semi-detached in Hounslow and Feltham; riverside new-build in Brentford. Chiswick is one of west London's most conservation-controlled areas; outer Hounslow is permissive suburban. Read that before choosing a house extension route in Hounslow — construction, not postcode, sets what is achievable. Hounslow Council charges £548 for a householder application and has 8 weeks to determine it.
Sources for this Hounslow 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.
Almost half of the householder appeals against Hounslow succeed. Across 763 decisions between 2016 and 2026, 360 were allowed and 389 dismissed — 47.2%, against 39.0% across London — with a further 14 allowed in part. Hounslow also refuses a higher share of applications than most London boroughs, and those two facts belong together: a council that refuses readily generates appeals it does not win. The practical consequence is that a Hounslow refusal is worth costing an appeal against rather than treating as the end of the scheme, and that the officer's stated reason deserves reading closely, because it will be tested.
The median Hounslow appeal ran 64 days from start to decision, and that clock starts only once the council's own determination period has already run — the practical argument for getting the first submission right. Just under one in ten, 70 cases or 9.2%, turned on a conservation area. All of them went by written representations, meaning an inspector read the drawings and the statement and saw nothing else.
Drawn from 763 householder appeals decided in Hounslow. Source: Planning Inspectorate casework. Licence: OGL v3.0. Everyone counted here was refused and then chose to press on, so the numbers describe how a fight ends, not how often Hounslow says yes.
Below are the queries that reach us most often from Hounslow addresses, each answered against this borough's own determination record rather than national averages.
Start a free quote →Plenty of Hounslow extensions still run on permitted development — a 3m or 4m single-storey rear, a side extension limited to half the original house width — but the borough's larger householder refusal record shows the wider allowances are no formality. Flats, listed buildings and conservation areas need full planning permission instead. We settle which route applies at the site survey.
Under permitted development a single-storey rear extension on a Hounslow house may project 3m from the original rear wall if the house is attached, 4m if it stands detached. The 6m and 8m depths are not automatic: they run through the larger householder prior approval procedure at Class A, paragraph A.4 of Schedule 2, Part 1 of the Town and Country Planning (General Permitted Development) (England) Order 2015, and Hounslow refused 215 of the 741 it determined, 29.0% (MHCLG planning statistics, retrieved 1 September 2026). Flats, listed buildings and addresses under an Article 4 direction have no such rights to begin with.
Budget a Hounslow extension in two parts. Ours covers the route through planning, the building regulations submission and the structural calculations, all at one agreed figure. The other is the build, priced by a contractor per square metre and moved by access, ground conditions and how the kitchen is specified. A side return infill is usually the cheaper square metre; a two-storey rear the dearer. See our fees.
Hounslow has no borough-specific basement policy, so a basement conversion is judged against the national framework and the Local Plan on structure, drainage and flood risk. That last test bites unevenly: Environment Agency mapping puts 9.74% of the borough's 55.96 km² in Flood Zone 3 and 12.73% in Zone 2. The zone settles one question only — whether a Flood Risk Assessment is required with the application. A Thames Water Build Over Agreement is a separate consent again, triggered within 3m of a public sewer.
A Chiswick or Turnham Green terrace usually has room for both. The side return takes the narrow passage beside the house and turns it into kitchen width; the rear extension buys garden depth. Do both and it becomes a wraparound. Which one earns its cost depends on where the existing kitchen wall sits, and that is a site-visit question rather than a plan-drawing one.
The Edwardian villas and terraces around Chiswick and Turnham Green take a single-storey rear kitchen extension or a side-return infill comfortably, and the semi-detached stock further west has the plot depth for a double-storey rear. A wraparound does both directions at once. Which is genuinely viable gets settled on the survey rather than from a floorplan on a listing site.
We cover all Hounslow postcodes — W3, W4, TW3, TW4, TW5, TW7, TW8, TW13, TW14 — with local surveyors. Survey appointments within 3 working days.
Hounslow decides almost everything at officer level: 3,872 of 3,929 determinations in the period were taken under delegated powers, 98.5% (MHCLG planning statistics, retrieved 1 September 2026). What those officers read for is materials that match or complement the existing house, the effect on a neighbour's amenity, and Part L. Where the planning history is tangled, a pre-application advice summary goes in with the drawings.
If your property sits on a boundary, here are the neighbouring options.
In Hounslow a household extension is refused about as often as a small development scheme, which is not how most of London behaves. Householder decisions were refused 695 times out of 2,310 here, a rate of 30.1%; minor schemes 347 times out of 1,010, or 34.4%. Pooled across the 33 boroughs those two rates are 17.0% and 22.1% (MHCLG planning statistics, retrieved 1 September 2026). One CIAT-affiliated team covers the drawings, the structure and the submission.
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