Basement conversion in Northwood

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

Hillingdon’s Northwood Town Centre, Green Lane Conservation Area Appraisal, adopted in September 2019, describes a relatively small conservation area centred on the Green Lane and Maxwell Road junction, taking in Station Approach and most of the residential Maxwell and Murray Roads. Green Lane was a quiet country lane until Northwood Station opened in 1887; by 1891 Frank Murray Maxwell Hallowell Carew had laid out the roads, naming them after himself and his family, and sold all the plots. The historic buildings are mainly red brick under red clay tiles, with gables, half timbering, sash windows, leaded lights and chimney stacks.

Hillingdon’s November 2009 leaflet describes the Northwood-Frithwood conservation area, designated in 1989, as primarily large, individually designed detached houses in the Arts and Crafts style on the estate Frank Carew developed after the Metropolitan Railway arrived in 1887, with later houses by C.H.B. Quennell, Swanell and Sly and John Markham, on roads lined with mature trees. Hillingdon’s local list includes Quennell houses of about 1910 at 5 Carew Road, in red brick under a sweeping tiled hipped roof, and a line of his houses at 10–16 Eastbury Road.

The Glen, a conservation area since July 2007, is a 1950s planned estate of maisonettes on the south side of Green Lane, designed by Kenneth C. Saunders, Architects, and built in 1958 and 1959 in brown brick, with white-painted casements and brown tiled roofs with bonnet hips. Hillingdon’s Area of Special Local Character maps for the Copsewood and Gatehill Farm estates take in Copse Wood Way, Nicholas Way, Gatehill Road and Elgood Avenue; the 2023 townscape study illustrates its large suburban type with Nicholas Way, describing substantial houses on large plots, many with a strong Arts and Crafts influence.

Local design and consent context

Hillingdon lists three conservation areas in Northwood. Northwood Town Centre, Green Lane, recorded by Planning Data as CA-36, was designated on 2 December 2009 after Cabinet approved it on 15 October 2009, and its appraisal, adopted in September 2019, is a material consideration in planning decisions. Northwood, Frithwood (CA-15) dates from 1989 and was extended in 2009; the council’s list offers a map and a November 2009 leaflet for it. The Glen, Northwood (CA-38) was designated on 18 July 2007.

The Glen has its own appraisal and management plan, both dated March 2008. Hillingdon says planning applications in a conservation area should come with a heritage statement and take account of any appraisal and management plan, and that it will generally not permit the demolition of buildings that make a positive contribution to the area’s character or appearance. The Frithwood and Glen leaflets, from November 2009 and June 2007, describe the rules as they then stood, so check the current rules with Hillingdon rather than relying on them.

Hillingdon has 15 Areas of Special Local Character, which it describes as non-designated local heritage assets. Its list includes Dene Road, Northwood (13 November 1989), Old Northwood (31 March 2005) and Hillside, Northwood Hills (24 July 2008), and gives the Copsewood Estate and the Gatehill Farm Estate, Northwood, a designation date of “Not applicable”. Policy DMHB 5 asks alterations in these areas to respect the established scale, building lines, height, design and materials, and extensions to be subservient, leaving space for landscaping.

Access and site planning

For a Hillingdon address, the council permits building work audible at the site boundary from 8am to 6pm, Monday to Friday, and 8am to 1pm on Saturday, and not on Sundays, public or bank holidays. In a flat or maisonette, ask the managing agent or residents’ association about any building rules on noise, deliveries and shared parts. If you stay at home, agree which rooms remain in use and when water or power will be off, and tell neighbours in advance what is planned.

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

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