Rear extension design for a period house in Stanmore conservation area, Harrow

Stanmore · HA7 · Harrow

Rear Extension Drawings in Stanmore HA7

Fixed-fee, MCIAT-chartered rear extension drawings for Stanmore (HA7) homeowners — London Borough of Harrow validation and local constraints handled from the start.

Stanmore (HA7) sits on the wooded high ground of north Harrow, where Georgian cottages on Stanmore Hill and large period houses along Old Church Lane make rear and side extensions a careful design exercise rather than a routine build.

Two conservation areas plus Harrow's Article 4 directions mean front-facing works and many minor alterations here need consent, so we always check the exact boundary and Article 4 status before deciding between permitted development and a full householder application.

Proposed floor plan

Stanmore HA7

Stanmore (HA7) — planning at a glance

Council: London Borough of Harrow
Postcode district: HA7
Planning portal: View the Harrow planning portal
Housing stock: Stanmore Hill mixes Georgian and Victorian cottages with grand detached villas on one of the highest points in London. Old Church Lane, of medieval origin around the 1632 old church, carries substantial period houses in mature wooded plots.
Article 4: Harrow has made Article 4 directions across its Stanmore conservation areas, removing permitted-development rights for front-facing changes such as windows, doors, roofs and boundary walls.
Conservation: Stanmore Hill Conservation AreaOld Church Lane Conservation Area
Sample streets: Stanmore Hill · Old Church Lane · Dennis Lane · Green Lane
Local constraints: Stanmore Hill and Old Church Lane conservation-area controls on front elevations, roofs and boundary treatmentsArticle 4 restrictions requiring permission for otherwise-permitted alterationsMature tree cover and likely TPOs on the wooded hillside plots

Planning in Stanmore (HA7): what to know before you apply

Inside the Stanmore Hill or Old Church Lane conservation areas, expect a full householder application for most visible work and reduced permitted-development scope under Article 4. Rear extensions can still succeed where scale, materials and tree impact respect the historic setting.

Typical Stanmore housing stock

Stanmore Hill mixes Georgian and Victorian cottages with grand detached villas on one of the highest points in London. Old Church Lane, of medieval origin around the 1632 old church, carries substantial period houses in mature wooded plots.

Streets we regularly draw for in Stanmore

Stanmore Hill · Old Church Lane · Dennis Lane · Green Lane

What HA7 is actually built of

Measured from 131 classified residential buildings in HA7, not from a description of the area.

Stanmore HA7 housing mix

Residential building form across the HA7 postcode district, from 131 classified buildings.

Attached on more than one side	27%
Attached on one side	55%
Detached	18%
Median building footprint	78 m²
Addresses per buildingAbove about 2 means flats and maisonettes dominate	1.63
Buildings classified	131

Source: Ordnance Survey National Geographic Database (derived statistics). Contains OS data © Crown copyright and database right 2026. Contains Royal Mail data © Royal Mail copyright and database right 2026. Extracted 2026-08-17.

Rear Extension Drawings for Stanmore (HA7) homes: the package and the process

Depth is the number the application turns on, and it has to be measured from the original rear wall of the house rather than from whatever is there now. The drawings carry that dimension, the eaves and ridge heights, the position of any rooflight, and the boundary distances on both sides.

Where the scheme goes beyond the standard allowance and relies on the larger home extension route, the drawings serve a second purpose: they are what the council sends to the neighbours during the consultation. A clear, dimensioned proposed elevation answers the objection about overshadowing before it is made.

Depth is limited by the plot as much as by the rules. A long garden behind a terrace can take the full allowance, while a short one runs out before the rules do — and on a semi or detached house the same depth reads very differently from the boundary.

Do I need planning permission for a rear extension in London?

Many single-storey rear extensions qualify as permitted development, meaning no planning application is needed, provided depth, height and materials stay within set limits. That changes if your property sits in a conservation area or is subject to an Article 4 direction, both of which can remove permitted development rights across a street or borough — in that case a full householder planning application is required regardless of size.

Even where an extension qualifies, most homeowners obtain a Lawful Development Certificate to confirm that status in writing before building — useful for mortgage lenders, buyers and Building Control. We check your property against your borough's constraints before recommending a route.

How deep can a single-storey rear extension go?

Depth is the main constraint on a rear extension, and it depends on your house type and whether you use standard permitted development or the larger home extension scheme.

Permitted development

Standard permitted development allows a single-storey rear extension up to 3 metres deep for terraced and semi-detached houses, or 4 metres for detached houses, generally with eaves height limited to match or stay close to the existing house.

Larger home extension scheme

The prior-approval scheme extends this to 6 metres for terraced and semi-detached houses and 8 metres for detached houses. Your council writes to affected neighbours; if none object within the notification period, approval follows without a full planning application. If an objection is raised, the council assesses the impact on neighbouring light and outlook itself, rather than automatically refusing, so a well-considered design still has a good chance of approval.

Designing the kitchen-diner: rooflights, bi-folds and daylight

Most rear extensions exist to create one open-plan kitchen, dining and living space, so the drawing work focuses on getting light and flow right within the depth you are allowed.

Structural opening sized for bi-fold or sliding doors across most of the rear elevation
Rooflights or a roof lantern positioned to light the centre of the room, away from the shadow line of the main house
Open-plan layout tested against the 45-degree rule, which protects daylight to your neighbours' windows and can limit how close a flank wall or roof comes to the boundary
Floor build-up and threshold detail coordinated so the new floor meets the existing one without a step

Rear extension routes at a glance
Route	When it applies	Typical fee
Permitted development (Lawful Development Certificate)	Depth within 3m (terraced/semi) or 4m (detached), height and materials within PD limits	PD/LDC pack ~£950–£1,450
Larger home extension (prior approval)	Depth up to 6m (terraced/semi) or 8m (detached), with neighbour notification	from £1,100
Full householder planning permission	Extension exceeds PD/larger-home limits, or the property is in a conservation area with an Article 4 direction	Full Planning pack ~£1,600–£2,400
Planning + Building Regulations (structural)	Combined planning and construction-ready pack with structural calculations for the opening and roof	Planning + Building Regs pack ~£2,200–£3,850

Sheet from a rear extension drawings package drawn for a Stanmore property in HA7, showing the existing and proposed arrangement at scale — A sheet from the rear extension drawings package we submit to London Borough of Harrow for Stanmore (HA7) properties.

Also in Stanmore HA7

Planning Permission Planning Drawings Architectural Drawings Building Regulations Drawings Loft Conversion Drawings Rear Extension Drawings across Harrow Rear Extension Drawings across London

FAQ

Rear Extension Drawings in Stanmore HA7 — FAQs

How much does a rear extension cost to design in London?+

Rear extension drawings start from £1,100, with the final fee set by the route your extension takes — permitted development, prior approval or full planning — and whether you need building regulations and structural calculations bundled in. The fee is fixed and agreed upfront.

Do I need an architect for a rear extension?+

No. DrawingsDirect is an MCIAT-chartered architectural technologist practice, producing the same council-accepted drawings as an architect for a fixed fee typically around 30% lower.

How long does it take to get rear extension drawings?+

Drawings are typically ready around 7 days from survey. Once submitted, councils have a statutory 8-week period to determine a standard householder planning application.

What is the 45-degree rule?+

It is a daylight test many London councils apply to check that a rear extension does not block too much light to a neighbour's nearest window, measured as a line drawn at 45 degrees from that window. We check it before submission, not after a refusal.

Will I need a Party Wall Agreement for a rear extension?+

Only if your foundations or new walls sit on or near the boundary with a neighbouring property. A straightforward rear extension set within your own plot often does not trigger the Party Wall etc. Act 1996, unlike a Side Return or Wraparound extension, which usually does.

Do I need planning permission for a loft conversion in Harrow?+

Harrow's Metro-land semis and detached houses in Rayners Lane, Kenton and Stanmore suit hip-to-gable and dormer lofts, which frequently qualify as permitted development within the volume limits. The exceptions are the conservation areas — Harrow on the Hill and Pinner's historic core — and the Article 4 wards. We check your address and can confirm permitted development with a Lawful Development Certificate.

What does Harrow expect for a rear extension on a 1930s semi?+

The council pays close attention to preserving the rhythm and building line of its interwar suburban streets, so extensions are expected to respect the established line and roof form. Many single-storey rear extensions still fall within permitted development; where a full application is needed, we design to the borough's residential guidance so it validates and approves without repeated revisions.

Can I extend a home in Harrow on the Hill or Pinner?+

Yes, but these historic conservation areas carry a heritage setting and long views the council protects closely, so permitted development is often restricted and a full, context-led application is required. We design to the character of the area — materials, proportions and rooflines — and evidence the heritage considerations so the submission stands up.

How long does Harrow Council take to decide?+

Harrow determines most householder applications within the statutory eight-week period once validated. The commonest delay is a validation query, so we prepare Harrow submissions to the council's checklist with correctly scaled existing and proposed drawings and a location plan to keep the application on track.

How much do planning drawings cost in Harrow?+

We work to a fixed fee agreed upfront, usually around 30% below an architect's charge for the same council-accepted drawings, with free redraws until Harrow approves. The figure depends on the scheme — a dormer loft differs from a double-storey extension — so we confirm it once we understand your project rather than billing by the hour.

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