Basement conversion in Pinner

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 Pinner High Street conservation area, designated in 1968, is in its appraisal’s words a remarkable survival of a medieval village, with timber-framed buildings, some listed, from as early as the 15th century. Many have brick facades and tiled roofs, often relatively steeply pitched; timber-framed walls were historically rendered or weatherboarded, and the appraisal records timber sashes, lattices and casements from every century since the 15th. The grade II* Church of St John the Baptist, with 14th- and 15th-century work, is the area’s oldest building, and 25–27 High Street was originally a Wealden hall house, rare in Middlesex.

The Pinner Hill Estate conservation area, designated in 1990, is characterised by detached houses on large plots with spacious rear gardens. After 1919, F. W. Griggs’s Country Garden Estates Ltd sold plots of at least half an acre, many houses were architect designed, and since the 1970s plots have been subdivided and houses extended or redeveloped. The appraisal records houses of up to three storeys in Art Deco, Tudor Revival, Arts and Crafts and Neo Classical inspired designs, mainly in hand-made brick, clay tile, timber and render, on roads that are private except Potter Street Hill and Potter Street.

Pinner’s population, 761 in 1801, reached 44,392 by 1951, and the Metropolitan Railway station opened behind the High Street in 1885. Pinnerwood Park is a garden-suburb estate of inter-war cottage-style houses, Waxwell Close a crescent of red-brick semi-detached houses and Moss Lane a blend of Edwardian and 1930s Arts and Crafts-style houses. Borough-wide, Harrow’s Local Plan records a greater share of whole houses, and a lower share of flats, than the London average, its evidence base finds semi-detached housing the borough’s most common type, and the Pinner Road appraisal notes several 1930s blocks of flats in the Pinner area.

Local design and consent context

On Pinner Hill, a direction confirmed on 19 July 1990 covers hard surfaces, satellite antennas, gates, fences and walls and new accesses to a highway across the conservation area, except the listed golf club and farm, and one confirmed on 17 December 2002 covers the enlargement or alteration of a house, other roof alterations and porches, where fronting a highway, waterway or open space, at six named houses; Harrow notes these add to the standard conservation-area controls. At West Towers, a direction of 10 June 1991 covers enlargement or alteration, porches, antennas and the painting of exterior brickwork on front and exposed side elevations, and one of 23 October 2003 covers other roof alterations, such as rooflights or altered roof tiles.

In Pinnerwood Park, a direction in force from 10 June 1991 controls satellite dishes throughout and, in a defined core area, additions and alterations including replacing windows and doors other than at the rear; an Article 4(2) direction of 25 January 1996 extended similar controls to the outer areas. At East End Farm, named houses have controls on hard surfaces, and Dormer Cottage and 96 Moss Lane on enclosures as well, where development would front a highway, waterway or open space.

Policy HE1 supports proposals that preserve or enhance a heritage asset’s significance, with their impact assessed through a Heritage Impact Assessment, and its supporting text notes that below-ground development and changes to internal layouts can affect significance.

Access and site planning

For an address in Harrow, the council permits noisy construction work from 8am to 6pm, Monday to Friday, and 8am to 1pm on Saturday, with none on Sundays or bank holidays, and suggests giving neighbours advance warning of the work and its duration; residents should not carry out DIY before 8am or after 8pm. In a flat, ask the managing agent about building rules on hours, deliveries and common parts; if you stay at home, agree which rooms stay in use and when water or power will be off.

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The Pinner area guide · Basement conversion across London · Hampstead Architecture & Planning · Hampstead Chartered Surveyors

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