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Service area · London Borough of Harrow

Architectural Designers in Harrow

Magna Studio prepares planning and Building Regulations drawings for homeowners across the London Borough of Harrow. This is Metroland: the 1930s semi in Rayners Lane, Kenton, North Harrow, Pinner, Stanmore and Harrow Weald dominates our work, with two-storey side extensions, 4–6 m rear extensions, hip-to-gable lofts with rear dormers, and garden rooms. Around Harrow on the Hill and Pinner High Street the older houses sit in conservation areas, and the Green Belt wraps the north of the borough, so we check constraints before choosing a route.

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Planning authority
Harrow
Decision time
8 weeks statutory
Common work
Side extension
Quote
Within 24 hours
01Local context

Typical homes we work on in Harrow

  • 1930s semi-detached houses in Rayners Lane, North Harrow, Kenton, Belmont, Harrow Weald and Pinner
  • Detached inter-war houses in Stanmore, Hatch End, Pinner and around Harrow Weald Common
  • Victorian and Edwardian terraces in Wealdstone, Harrow town centre, Roxeth and West Harrow
  • Georgian and Victorian houses in Harrow on the Hill and Pinner village
  • Post-war estates in Rayners Lane, South Harrow and Wealdstone, with new-build flats around Harrow and Wealdstone town centres
02Planning permission

Do I need planning permission in Harrow?

Answer-first guides for the projects we see most here, with the national rules and the local constraints that change them.

03Constraints

Planning constraints in Harrow

What changes the planning route in this area. Always confirm on the council's constraints map before relying on permitted development.

Green Belt and Metropolitan Open Land

The north of the borough is Green Belt, including Harrow Weald Common, Stanmore Common, Bentley Priory, Pinner Park Farm and Old Redding, with Metropolitan Open Land at Harrow on the Hill and along the Yeading Brook. Extensions to houses in the Green Belt must not be disproportionate to the original dwelling, and outbuildings face a strict test.

Source · Checked 15 Sept 2026

Conservation areas

Harrow has around 28 conservation areas, including Harrow on the Hill, Pinner High Street, Pinnerwood Park Estate, Roxeth Hill, Harrow Weald Park, Stanmore Hill and Kerry Avenue. Roof extensions are not permitted development inside them and extensions are expected to be subordinate and in matching materials.

Source · Checked 15 Sept 2026

Article 4 directions

Pinnerwood Park Estate and several other conservation areas have Article 4 directions removing permitted development for front alterations, windows, boundary treatments and some roof works. The council has also considered a direction on small HMOs; check the constraints map and current position before relying on permitted development.

Source · Checked 15 Sept 2026

Residential Design Guide SPD

Harrow's Residential Design Guide SPD sets out expectations for rear extension depth, the set-back and set-down of two-storey side extensions, dormer size and position, and outbuildings. Officers apply it alongside the Development Management Policies on design and amenity.

Source · Checked 15 Sept 2026

Listed buildings

Harrow on the Hill, Pinner High Street, Headstone Manor and Bentley Priory contain concentrations of listed buildings, including several medieval and Tudor houses in Pinner. Listed building consent is needed for almost any alteration.

Source · Checked 15 Sept 2026

Local flood risk

The River Pinn, Yeading Brook and Wealdstone Brook put parts of Pinner, Eastcote Lane, Wealdstone, Kenton and Headstone in Flood Zones 2 and 3, with surface water flooding elsewhere. Ground-floor extensions there may need a flood risk statement.

Source · Checked 15 Sept 2026

What London Borough of Harrow planning officers look for

Harrow officers are, in our experience, reasonable on suburban householder work but apply the Residential Design Guide closely. Common refusal reasons are two-storey side extensions without a set-back from the front wall that create a terracing effect, rear extensions that fail the 45-degree test, front dormers, and box dormers that wrap the hip. Hip-to-gable lofts with rear dormers and 4–6 m rear extensions on ordinary 1930s semis are usually accepted. The council offers a paid pre-application service and decisions often run beyond 8 weeks, so allow 10–14 weeks.

Council links

Extensions and loft conversions in Harrow

Harrow is Metroland. Rayners Lane, North Harrow, Kenton, Belmont, Harrow Weald, Pinner and Stanmore are lined with 1930s hipped-roof semis on plots wide enough for a two-storey side extension and deep enough for a 4–6 m rear extension, with roofs that suit a hip-to-gable conversion and rear dormer. Gardens are long, so garden rooms and home offices are common. A large share of this work is possible under permitted development (PD), and we secure a Lawful Development Certificate (LDC) as proof.

Wealdstone, Roxeth and West Harrow are Victorian and Edwardian terraces, where side-return infills and rear dormers within the 40 m³ allowance are the standard moves. Harrow on the Hill and Pinner village are different: Georgian, Victorian and, in Pinner, medieval and Tudor houses inside conservation areas, many of them listed, where work is slower and more careful. Flats in the new town-centre blocks and on estates have no householder PD rights.

Planning constraints in Harrow

  • Green Belt across the north of the borough, from Harrow Weald Common to Stanmore Common and Bentley Priory, where extensions must be proportionate to the original house.
  • Around 28 conservation areas, including Harrow on the Hill, Pinner High Street, Pinnerwood Park Estate and Stanmore Hill, where roof extensions lose PD rights.
  • Article 4 directions in Pinnerwood Park and other conservation areas, and possibly for HMOs.
  • Residential Design Guide SPD setting depth, set-back and dormer expectations.
  • Listed buildings in Harrow on the Hill, Pinner, Headstone Manor and Bentley Priory.
  • Local flood risk along the Pinn, Yeading Brook and Wealdstone Brook.

If you are unsure which of these affect your plot, start with the council’s constraints map or ask us to check as part of your quote.

What Harrow planning officers look for

Officers assess householder applications against the Development Management Policies and the Residential Design Guide SPD. The recurring tests are the 45-degree line from the neighbour’s nearest habitable window, a clear set-back and set-down for two-storey side extensions to avoid a terracing effect, rear extension depth relative to the neighbours, and dormers kept below the ridge, inside the roof slope and clad in matching tiles. Loss of daylight and outlook to a neighbour’s rear rooms is the most common refusal. The council offers paid pre-application advice, worth using in conservation areas and the Green Belt. Council fees from April 2025 are £528 for a householder application and £264 for a proposed-use LDC; verify before applying.

Our services in Harrow

Example projects nearby

Guides

Read Permitted development rights in London and Householder planning applications in London.

Ready to start in Harrow? Get an instant estimate: your indicative fee on screen and by email in two minutes, then a written fixed-fee quote within 24 hours.

04Examples

Example projects in and around Harrow

Proposed ground floor plan of a two-storey rear extension and side infill to a 1930s semi in EalingExample project
Two-storey extensionNorthfields, Ealing

Two-Storey Extension in Northfields, Ealing

Two-storey rear extension with a single-storey side infill to a 1930s semi-detached house, adding a kitchen-dining room, a fourth bedroom and a family bathroom.

Typical route: Householder planning application for both storeys in one submission

Proposed ground floor plan of a side extension and garage conversion to a 1930s semi in Finchley, BarnetExample project
Side extensionFinchley, Barnet

Side Extension and Garage Conversion in Finchley, Barnet

Conversion of an attached garage and a single-storey side extension behind it to a 1930s semi-detached house, widening the kitchen and adding a utility room and WC.

Typical route: Householder planning application, as the width exceeds the PD limit

05Questions

Planning questions we hear in Harrow

Do I need planning permission for a side extension in Harrow?

A single-storey side extension no wider than half the original house and no higher than 4 m is usually permitted development on a semi outside a conservation area. A two-storey side extension always needs planning permission, and Harrow expects it to be set back from the front wall and set down from the main ridge so the pair of semis does not read as a terrace.

Can I convert my loft under permitted development in Harrow?

On a 1930s semi in Rayners Lane, Kenton, Pinner or Stanmore outside a conservation area, usually yes: a hip-to-gable and rear dormer within 50 m³ is typically lawful with nothing to the front. In Harrow on the Hill, Pinner High Street, Pinnerwood Park and other conservation areas roof extensions need permission. We recommend a Lawful Development Certificate.

Is my house in the Green Belt in Harrow?

If you live near Harrow Weald Common, Stanmore Common, Old Redding, Bentley Priory or Pinner Park Farm, quite possibly. Extensions are allowed in principle but must not be disproportionate to the original house, and garden buildings are judged strictly. Check the Local Plan policies map or ask us to confirm as part of your quote.

Can I build a garden room in Harrow without planning permission?

Usually yes, outside the Green Belt and conservation areas. An outbuilding up to 2.5 m high within 2 m of a boundary, covering no more than half the garden and used for something incidental to the house, such as an office or gym, is permitted development. It cannot be a bedroom or a self-contained annexe. We can certify it with a Lawful Development Certificate.

How long does Harrow council take to decide a householder application?

The statutory period is 8 weeks from validation, and 8 weeks for a Lawful Development Certificate. Harrow often agrees an extension of time, so we advise allowing 10–14 weeks and submitting complete, fully dimensioned drawings.

06Coverage

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