Back-of-house extension drawings for Harrow homes — the glazed kitchen-diner across the rear, drawn to Harrow Council's depth and daylight limits, delivered in days and revised free until your decision, with a free approval-odds check first.
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.
The rear extension is the workhorse of Harrow home improvement — it is how a dark back kitchen becomes an open family room facing the garden. Because the borough is built largely from interwar Metroland semi-detached houses, Edwardian terraces around the stations and detached homes on the hill, most back walls sit close to a neighbour on at least one side, and that proximity, not the design, is what Harrow Council scrutinises. The council reads the proposal against Harrow Local Plan and the Residential Design Guide SPD, and the first line an officer draws is the 45-degree splay from the neighbour's nearest window.
So the drawings live or die on geometry. We set the depth against the exact permitted-development figure, hold the eaves and the flat-roof or lantern build-up under the 4-metre height ceiling, and show the projection tested against both the 45-degree plan angle and the 25-degree section angle to the neighbouring windows. 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 the rear elevation is composed around it rather than corrected after an objection.
Where the property sits in a conservation area — Harrow on the Hill, Pinner High Street, Pinner Village, Roxeth and Harrow Weald among Harrow's — the larger-home extension route is switched off and even a modest rear addition needs consent. Harrow on the Hill and the Pinner conservation areas carry tight controls, and several streets have Article 4 directions removing permitted-development rights. We confirm the designation before the survey.
Many single-storey rear extensions in Harrow are permitted development and need no application. You will normally need to apply to Harrow Council, or use the larger-home prior-approval route, if any of these apply:
We draw the depth, the roof build-up and the daylight splays to each neighbour on the page — the tests Harrow Council's officers apply first — and submit a validation-complete pack, whether that is a lawful development certificate, a larger-home prior-approval notice or a full householder application.
Below is Harrow Council's real householder decision record, taken 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. Rear extensions turn most often on neighbour daylight and depth, so a drawing pack that proves those tests upfront is decided faster and refused less often than a DIY submission.
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 approved rear extension is typically a single-storey glazed box within the depth limit, roofed either flat with a lantern or in a shallow mono-pitch, and finished in brick or render to match the host wall. On the borough's interwar metroland semi-detached houses, keeping the projection to the permitted-development figure often avoids an application entirely; where owners want the full 6 metres, the larger-home route succeeds when the neighbour-consultation period passes without a sustained objection.
The borough resists loss of the gaps between semis that define Metroland streets. We keep the extension inside the daylight splays, set any glazed roof below the first-floor cill, and retain the garden depth Harrow Council expects — so the back elevation answers the amenity case before a neighbour can lodge one. Two-storey rear extensions we draw with the 7-metre boundary gap and privacy screening resolved on the plan.
We draw rear extensions on every street in the borough. A few of the neighbourhoods where Harrow back-of-house projects come up most often:
Rear extension drawings for Harrow on the Hill's historic hilltop conservation area — depth-checked, daylight-tested and drawn to Harrow Council's guidance.
Rear extension drawings for Pinner's the medieval High Street and Metroland semis — depth-checked, daylight-tested and drawn to Harrow Council's guidance.
Rear extension drawings for Stanmore's detached and semi-detached interwar houses — depth-checked, daylight-tested and drawn to Harrow Council's guidance.
Rear extension drawings for Wealdstone's Edwardian terraces near the town centre — depth-checked, daylight-tested and drawn to Harrow Council's guidance.
Rear extension drawings for Rayners Lane's classic Metroland semi-detached estates — depth-checked, daylight-tested and drawn to Harrow Council's guidance.
Rear extension drawings for Kenton's 1930s hipped-roof semis — depth-checked, daylight-tested and drawn to Harrow Council's guidance.
How far you can extend at the back in Harrow depends on your house type and the route you take. This is how the options compare.
| Route | Depth allowed | Consent needed | What Harrow Council checks |
|---|---|---|---|
| Standard permitted development | 3m terrace/semi · 4m detached | Lawful development certificate (optional) | Depth, 4m height, materials |
| Larger-home prior approval | 6m terrace/semi · 8m detached | Prior-approval notice + neighbour consultation | Neighbour objections on amenity |
| Full householder application | Beyond the above, or two-storey | Full planning permission | Daylight (45°/25°), bulk, garden retained |
| Conservation area | Case by case | Full planning permission | Character, roof form, boundary treatment |
The larger-home route is switched off on designated land — conservation areas such as Harrow on the Hill and Pinner High Street and Article 4 streets need a full application.
A fixed process built around how Harrow Council validates and decides rear-extension applications — most drawings are submission-ready within seven days of survey.
Send us your Harrow postcode and house type. We confirm your conservation and Article 4 status, how much rear-extension depth you have under permitted development, and score your odds against live Harrow Council decisions.
We measure the original rear wall, floor and eaves levels, side and rear boundary distances and the neighbours' window positions — the numbers the depth limit and daylight splays depend on.
Chartered designers develop the single or two-storey rear extension to your brief, drawn inside the permitted-development limits or to Harrow Council's extension design guidance, with the daylight angles shown.
We submit the certificate, prior-approval notice or application, handle validation and case-officer queries, and revise the drawings free until Harrow Council issues its decision.
Often not. 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 involve Harrow Council for anything deeper via the larger-home route, for two-storey rear extensions, and for any rear extension in a conservation area such as Harrow on the Hill and Pinner High Street, where those permitted-development rights fall away.
The larger-home extension scheme lets a single-storey rear extension reach 6 metres on a terrace or semi, or 8 metres on a detached house — double the standard allowance. It is not automatic: you submit a prior-approval notification to Harrow Council, neighbours are consulted, and if one objects on amenity grounds the council rules on it. It also does not apply on designated land such as Harrow's conservation areas.
It is the daylight test Harrow Council applies to protect neighbours. Drawn on plan, a line at 45 degrees from the midpoint of the neighbour's nearest ground-floor window should not be crossed by your extension; a companion 25-degree line is checked in section. If the projection breaches it, the extension is likely to be shortened or refused, so we test and prove it on the drawings before submission.
A two-storey rear extension almost always needs a full householder application to Harrow Council, as it sits outside permitted development on most homes. The council checks that it stays at least 7 metres from the rear boundary, does not overbear the neighbours and avoids new overlooking. We resolve the boundary gap, privacy and daylight on the plans so the application is decided on its merits.
Frequently, yes. If the rear extension involves work to a shared wall, building up to the boundary, or excavating foundations near a neighbour's structure, the Party Wall etc. Act applies and you must serve notice — this is separate from Harrow Council's planning decision. We flag it early and can prepare the drawings a party-wall surveyor needs alongside the planning set.
We price each Harrow rear extension on its own footprint and send a fixed, no-obligation quote within one working day. It covers the full drawing pack with free revisions until Harrow Council approves, and we confirm at the outset whether your extension is permitted development, needs prior approval, or a full application. Call 020 7864 7245 to begin.
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