Basement conversion in Harrow on the Hill

Investigate the structure and ground before design.

Start with the basement conversion brief

Distinguish an existing cellar conversion from excavation for a new basement. Record levels, drainage, access and the adjoining structures, and obtain project-specific ground and structural investigations before relying on a design or budget.

Plan temporary works, waterproofing, ventilation, escape and spoil removal as part of the same brief. Ask Hampstead Chartered Surveyors to assess party-wall matters and Hampstead Architecture & Planning to coordinate the design requirements. An area name alone does not establish ground conditions.

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.

Elsewhere the mix changes. The Harrow Park appraisal records the road Harrow Park as mostly characterised by substantial buildings divided into flats, and Julian Hill as mostly single houses; Sudbury Hill is predominantly yellow stock brick under grey slate, with stucco especially on Regency and early Victorian properties; South Hill Avenue is essentially detached housing, with properties built between 1910 and 1930 on Orley Farm Road and Hill Close inspired by the Garden Suburb ideal; and Roxeth Hill mixes Edwardian villas, Arts and Crafts inspired terraces and 1930s semi-detached houses.

Local design and consent context

As of 8 February 2007, an Article 4(2) direction covers the Village properties its schedule lists: on elevations fronting a highway, waterway or open space, alterations including replacement windows and doors, roof alterations including roof lights and replacement tiles or slates, porches, gates, fences and walls, satellite antennas and exterior painting other than windows and doors, such as painting previously unpainted brickwork, need planning permission; hard surfacing needs it only at a shorter list of addresses.

Two further Village directions, confirmed on 5 October 2021, withdraw the permitted development right to demolish all or part of any gate, fence, wall or other means of enclosure fronting a highway, waterway or open space at the numbered properties in their schedules. On the Mount Park Estate, a 1990 direction over all land covers hard surfaces, satellite antennas, gates, fences and walls and new accesses to a highway, and a 2021 direction covers demolishing gates, fences and walls. South Hill Avenue has 1991 and 2021 directions on its hatched land, and in Roxborough Park and The Grove the directions name Chalgrove, Grove End and The Gables.

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

Harrow permits noisy construction work from 8am to 6pm, Monday to Friday, and 8am to 1pm on Saturday, with no noisy work on Sundays or bank holidays. It notes that the Control of Pollution Act 1974 gives it powers to limit working hours and suggests giving neighbours advance warning of the work and its duration. In a flat, ask the managing agent about any building rules on working hours, deliveries and common parts, and if you stay at home, agree which rooms remain in use and when water or power will be off.

Continue planning

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

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