Single-storey, double-storey, rear and side extension drawings for Harrow homes — measured to Harrow Council's design guidance, delivered in days and revised free until your decision, with a free approval-odds check before you commit.
Harrow Council granted 83% of the householder planning decisions it made in its latest published year — 4 points below the 87% England-wide householder average. Hip-to-gable conversions dominate because so much of the stock is hipped 1930s semis — roof bulk and the pair's balance are the tests, which is where a policy-literate drawing pack earns its keep. Its dominant Edwardian (1901–1910) and interwar (1918–1939) housing stock sets the design brief on most streets.
The permitted-development ceilings are fixed: 40m³ of new roof volume for a terraced loft and 50m³ for a semi or detached house under Class B, plus a 3m single-storey rear extension on a terrace or 4m on a detached house under Class A. Harrow carries at least one Article 4 direction, and conservation areas including Harrow on the Hill, Pinner High Street and Pinner Village remove those rights outright, so we confirm your exact address before a line is drawn. A validated householder application in Harrow is determined against an 8-week statutory target.
Harrow on the Hill (historic hilltop conservation area), Pinner (the medieval High Street and Metroland semis), Stanmore (detached and semi-detached interwar houses), Wealdstone (Edwardian terraces near the town centre), Rayners Lane (classic Metroland semi-detached estates) and Kenton (1930s hipped-roof semis) — these are the Harrow pockets our drawings cover most. Heritage designations here include Harrow on the Hill, Pinner High Street, Pinner Village, Roxeth and Harrow Weald. Harrow Council weighs each proposal against Harrow Local Plan and the Residential Design Guide SPD, where the borough resists loss of the gaps between semis that define Metroland streets. On roofs the borough is hipped roofs on the 1930s semis and steeper gabled roofs in Pinner village, over interwar Metroland semi-detached houses, Edwardian terraces around the stations and detached homes on the hill.
Harrow homes come in a handful of recurring shapes, and each one points to a different extension. The borough is built largely from interwar Metroland semi-detached houses, Edwardian terraces around the stations and detached homes on the hill, so a Victorian terrace usually wants a rear or side-return infill, while an interwar semi has room for a wider single-storey wrap or a two-storey side addition. Harrow Council judges every one of them against Harrow Local Plan and the Residential Design Guide SPD, weighing footprint, height and the impact on the house next door before it looks at the elevations.
That is why the drawings decide the outcome. We set the extension depth against the permitted-development limits precisely, keep the eaves and ridge within the allowances, and plot the 45-degree daylight lines to the neighbours' windows so the case officer can see the amenity test is passed. Hip-to-gable conversions dominate because so much of the stock is hipped 1930s semis — roof bulk and the pair's balance are the tests, so we design around it from the first sketch rather than discover it at validation.
Harrow also protects whole streets — Harrow on the Hill, Pinner High Street, Pinner Village, Roxeth and Harrow Weald among them. Harrow on the Hill and the Pinner conservation areas carry tight controls, and several streets have Article 4 directions removing permitted-development rights. On designated land the larger-home extension route and most side extensions stop being permitted development, so we confirm your address against those layers before drawing a line.
Plenty of Harrow extensions are permitted development and need no planning application — a single-storey rear extension within the depth and height limits is the common case. You will normally need to apply to Harrow Council if any of these apply:
We draw the footprint, the ridge and eaves heights and the neighbours' daylight on the page — the relationships Harrow Council's officers weigh first — and submit a validation-complete pack, whether that is a lawful development certificate, a prior-approval notification or a full householder application.
Below is Harrow Council's real householder decision record, drawn from official planning statistics and refreshed as new data lands. Harrow grants a fair share of householder applications, with hip-to-gable roof bulk on Metroland semis and the spacing between paired houses the recurring considerations. A complete, policy-literate extension pack anticipates those pressure points before submission, which is why professionally drawn applications are decided faster and refused less often than DIY ones.
Source: MHCLG planning application statistics (householder decisions, rolling year). Compare every borough on our London approval-rate league table.
Tell us about your project and get a fixed, no-obligation quote back within one working day. If you don't need planning permission at all, we'll tell you that too — for free.
Across Harrow on the Hill, Pinner and Stanmore, the extension that lands most often is the single-storey rear addition — a glazed kitchen-diner across the back of the house, kept within the permitted-development depth or taken to a full application where the ground floor wants more. On the borough's interwar metroland semi-detached houses, a side-return infill frequently pairs with it to square off the plan; on wider detached homes on the hill, a two-storey side or rear extension can add a bedroom above without swallowing the garden.
The borough resists loss of the gaps between semis that define Metroland streets. We size the extension to the amenity and daylight tests, match the roof and materials to the host house, and keep enough garden to satisfy Harrow Council's space standards — so the scheme answers the borough's questions before an objection can raise them. Where permitted-development rights are used up or removed, we prepare the householder application to the council's extension design guidance instead.
We draw extensions on every street in the borough. A few of the neighbourhoods where Harrow projects come up most often:
Extension drawings for Harrow on the Hill's historic hilltop conservation area — footprint-checked, daylight-tested and drawn to Harrow Council's guidance.
Extension drawings for Pinner's the medieval High Street and Metroland semis — footprint-checked, daylight-tested and drawn to Harrow Council's guidance.
Extension drawings for Stanmore's detached and semi-detached interwar houses — footprint-checked, daylight-tested and drawn to Harrow Council's guidance.
Extension drawings for Wealdstone's Edwardian terraces near the town centre — footprint-checked, daylight-tested and drawn to Harrow Council's guidance.
Extension drawings for Rayners Lane's classic Metroland semi-detached estates — footprint-checked, daylight-tested and drawn to Harrow Council's guidance.
Extension drawings for Kenton's 1930s hipped-roof semis — footprint-checked, daylight-tested and drawn to Harrow Council's guidance.
The right extension in Harrow depends on your house type and how much garden you can give up. This is how the main options compare on planning route and what they add.
| Extension type | Permitted development? | What it adds | What Harrow Council checks |
|---|---|---|---|
| Single-storey rear | Often, within 3m/4m depth (6m/8m via prior approval) | Bigger kitchen-diner across the back | Depth, height, neighbour daylight (45°) |
| Side-return infill | Sometimes, if within width and height limits | Squares off an L-shaped ground floor | Width vs the original house, glazing to boundary |
| Two-storey rear/side | No — full application | Extra bedroom or bathroom above | Bulk, overlooking, 7m rear-boundary gap |
| Wraparound (rear + side) | No — full application | Whole-width open-plan ground floor | Combined footprint and garden retained |
Route depends on your street — conservation areas such as Harrow on the Hill and Pinner High Street and Article 4 directions can remove permitted-development rights.
A fixed process built around how Harrow Council validates and decides householder extension applications — most drawings are submission-ready within seven days of survey.
Tell us your Harrow postcode and house type. We confirm your conservation and Article 4 status, how much permitted-development depth you have left, and score your odds against live Harrow Council decisions.
We measure the existing footprint, floor and eaves levels, boundary distances and the neighbours' window positions — the numbers the depth limits and daylight tests depend on.
Chartered designers develop the single-storey, two-storey or side extension to your brief, drawn inside the permitted-development limits or to Harrow Council's extension design guidance.
We submit the certificate, prior-approval notice or application, manage validation and case-officer queries, and revise the drawings free until Harrow Council issues its decision.
Not always. A single-storey rear extension up to 3 metres deep on a terrace or semi, or 4 metres on a detached house, and no higher than 4 metres, is usually permitted development. In Harrow you will need to apply to Harrow Council for two-storey extensions, side extensions wider than half the house, anything forward of the front wall, deeper rear extensions under the larger-home prior-approval route, and any extension in a conservation area such as Harrow on the Hill and Pinner High Street.
Standard permitted development allows 3 metres on a terraced or semi-detached house and 4 metres on a detached one. The larger-home extension scheme can double that to 6 or 8 metres, but it needs a prior-approval notification to Harrow Council and a neighbour-consultation period, and it does not apply on designated land such as Harrow's conservation areas. We confirm which route your property qualifies for before drawing.
Two-storey and double-storey extensions almost always need a full householder application to Harrow Council, because they fall outside permitted development on most homes. The council looks closely at bulk, overlooking of neighbours and the 7-metre gap a two-storey rear extension must keep from the rear boundary. We design to those tests and show the daylight and privacy angles on the drawings.
A householder planning application in Harrow runs to a statutory eight-week target, a larger-home prior-approval notification to around six weeks including the neighbour-consultation period, and a lawful development certificate to eight weeks. Incomplete submissions stall at validation, so we submit a complete pack and manage officer queries to keep the decision on schedule. Harrow Council is the decision-maker.
Yes — planning permission and building regulations are separate consents, and almost every extension needs both. Planning governs whether you can build it; building control governs how it is built, covering structure, insulation, drainage and fire safety. We prepare the building-regulations drawings alongside the planning set so Harrow Council's building control or an approved inspector can sign the work off.
Every house and brief is different, so we price each Harrow extension individually and send a fixed, no-obligation quote back within one working day. It covers the full drawing pack with free revisions until Harrow Council approves, and we tell you upfront whether your extension qualifies as permitted development. Call 020 7864 7245 to get started.
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Same fixed quotes, same fast drawings — wherever your project is.