House extension in Harrow on the Hill

Connect the added space to the existing home.

Start with the house extension brief

Begin with how the new space will meet the old rooms, garden and circulation. A measured brief should record boundaries, levels, existing drains, neighbouring windows and the parts of the building you intend to keep.

Develop daylight, structure and services alongside the floor plan. Agree which openings and finishes are included, how the existing home will be protected during construction and which decisions need surveys or approval before a quotation.

The local building context

The Village conservation area, designated in 1968, lies on the western slope of Harrow Hill, within walking distance of Harrow town centre and Harrow on the Hill Station. Its appraisal says the Victorian era saw a significant proportion of its dwellings and streets built to house artisans and school employees. On Nelson Road, Crown Street and West Street, mostly two-storey terraced cottage rows follow the contours of the hill in yellow stock brick, some rendered, with slate roofs and sliding timber sashes. Across the Village, many buildings sit directly on the pavement, and few have off-street parking.

On the lower slopes, the Mount Park Estate appraisal describes late Victorian and Edwardian houses, mostly detached, typically two storeys with rooms in the roof and set well back in extensive mature gardens along Mount Park Road, a narrow private road with gated entrances at either end. Red brick, red plain tiles, steep roofs and timber casements and sashes are characteristic. In Roxborough Park and The Grove, Arnold Mitchell’s Arts and Crafts houses stand on Grove Hill and Peterborough Road, and Whitehall Road, Lowlands Road and Lansdowne Road have late Victorian and Edwardian red-brick semi-detached houses.

The name Harrow on the Hill and an HA1 postcode do not settle the council, a conservation area boundary, a listing, Article 4 coverage or the consent route. The Hill is not all HA1: the John Lyon School on Middle Road, in the same Harrow on the Hill ward as Harrow School, has an HA2 address. Confirm the council for the address, then check Harrow’s conservation area search and map, any Article 4 schedule, the list entries, the title or lease and the planning history.

Local design and consent context

The Council’s schedules give the Village as designated in 1968, Mount Park Estate in 1980, extended in 1982 and revised in 1988, and Roxborough Park and The Grove in 1980, extended in 1991 and May 2013. The appraisals record the designation of the Harrow School area in 1968, Harrow Park in July 1969, Sudbury Hill and Roxeth Hill in 1969 and South Hill Avenue in 1980. The adopted Local Plan says the detailed policies and guidance in such SPDs and appraisals can provide further material considerations, so ask Harrow how it weighs them for your proposal.

The 2008 SPD counted about 80 listed building entries within the Hill’s conservation areas and about 400 locally listed buildings on the Hill; Harrow now counts 909 locally listed buildings across the borough, protected locally by planning policy rather than by listing. Harrow’s April 2016 list gives ages for its entries, approximate in most cases, such as the fifteenth century for 3–7 West Street, about 1817 for Julian Hill and 1895 for St Margaret’s on Mount Park Road. Harrow Park, formerly Flambards, is a grade II registered park and garden, and St Mary’s Churchyard and Churchyard Extension and Grovefields on Grove Hill are locally listed parks and gardens.

The 2008 SPD says much of the green open space around the Hill is Metropolitan Open Land, and the adopted Local Plan records a substantial tract of it in the Harrow School and John Lyon School estates; Policy GI1 protects Metropolitan Open Land from inappropriate development, and the Mount Park appraisal notes that the designation reaches into some rear gardens. The 2008 SPD says a large part of the Hill is the “Historic Harrow” Archaeological Priority Area, and Historic England’s current record covers the core area of Harrow on the Hill; new basements in a priority area should be informed by consultation with the Greater London Archaeological Advisory Service.

Access and site planning

The 2008 SPD notes that the Hill’s smaller side roads are congested by the lack of off-street parking, so plan deliveries, waste and protection early. In Harrow, a skip on the public highway needs a skip licence, which the skip company obtains; scaffolding, hoardings and building materials on the highway each need a licence, with materials on the carriageway, not the footway. Allow up to 10 working days for a skip licence or a bay suspension, granted only in marked bays, and check on Harrow’s map search whether the street is in a controlled parking zone. The supporting text to Local Plan Policy M3 asks for highway approvals and licences at least 60 days before works start. On a private road such as Mount Park Road, ask who manages it before booking a skip.

Continue planning

The Harrow on the Hill area guide · House extension across London · Hampstead Architecture & Planning · Hampstead Chartered Surveyors

Discuss your project

Tell us what you are planning in Harrow on the Hill

Share the property location, the work you have in mind and any drawings or permissions you already have.

£5M public liability, £10M employers’ liability and contractors’ all risks cover.

Design support: Hampstead Architecture & Planning.
Surveying support: Hampstead Chartered Surveyors.