House extension in Pinner

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 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.

The name Pinner and an HA5 postcode do not settle the council, a conservation area boundary, a listing, Article 4 coverage or the consent route. Hillingdon Council gives its Eastcote Library an HA5 address, the Pinner SPD places Eastcote station outside Harrow, and at the southern end of Potter Street Hill the Pinner Hill Estate conservation area boundary runs into Hillingdon. Confirm the council for the address, then check that council’s conservation area maps and Article 4 schedules, the list entry and local list, the title or lease and the planning history.

Local design and consent context

The Local Plan says these SPDs and appraisals can provide further material considerations, so read the guidance for your area. For Pinner Hill, the 2009 management strategy encourages extensions at the rear and subservient to the house, protects front and side roofs from dormers and rooflights, asks for original features such as timber windows and doors to be kept and usually avoids change of use to flats. It records pressure for large extensions and hard-surfaced front gardens, and overuse of rooflights on South View Road.

Policy HO2 sets criteria for converting a house into self-contained flats, among them an internal floor area as originally built above 130 square metres, or one that could be accepted for extension to that size, at least one family-sized home of 74 square metres or more, and a site in an area of PTAL 3 to 6. Harrow’s Residential Design Guide SPD (2010), which is not statutory but is considered in planning applications, covers extensions and conversions of houses to flats.

Harrow’s 2009 SPD records that most of the Pinner Hill Estate conservation area and all of the Pinnerwood Farm conservation area are Green Belt, where planning controls on extensions, and especially on new development, are more stringent. Local Plan Policy GI1 considers Green Belt proposals in line with the NPPF, and its supporting text says that inappropriate development will not be approved except in very special circumstances, so ask Harrow whether a house or garden lies within the Green Belt before designing an extension.

Access and site planning

Plan deliveries, waste and protection for any shared hall or drive before work starts. In Harrow, a skip on the public highway needs a licence, which the skip company obtains, while one on private land does not; scaffolding on the highway needs a licence issued to the company erecting it; building materials on the highway need a licence even if placed there only temporarily, and so does a hoarding. Bay suspensions are granted only in marked bays and can take up to 10 working days. Most Pinner Hill Estate roads are private, so confirm with Harrow which licences apply there before booking.

Continue planning

The Pinner area guide · House extension across London · Hampstead Architecture & Planning · Hampstead Chartered Surveyors

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