House extension in Northwood

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

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.

The name Northwood and an HA6 postcode settle none of the questions that matter. Hillingdon’s Gatehill Farm Estate map shows administrative boundary lines along the estate’s northern edge, and beyond them Admiralty House lies in Three Rivers District Council’s Frith Wood Conservation Area, so confirm the council with the government’s finder first. Then check the conservation area and Area of Special Local Character maps, the listed and locally listed building records, Hillingdon’s Article 4 directions, the title or lease, any residents’ association rules and the planning history, including conditions on earlier permissions.

Local design and consent context

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.

Local Plan Part 2 has special policies for the Gatehill Farm Estate and Copse Wood Estate: new development is expected to conform to the vernacular styles predominant there, with traditional roof forms and architectural features, and to relate to its landscaped setting. Policy DMHB 6 asks new houses there to keep similar plot widths and building lines, unobtrusive boundaries in natural materials, at least 1.5m to side boundaries and the mature trees. Under Policy DMHD 1, two-storey side extensions there should be set in at least 1.5 metres from the side boundary, and most Copse Wood Estate trees carry preservation orders.

Hillingdon lists five Article 4 directions, none of them a conservation-area direction for Northwood householders. The one that reaches ordinary house extensions is borough-wide: in force from 22 September 2014, it removes permitted development rights for a single-storey rear extension reaching more than 4 metres beyond the rear wall of the original house. The sealed direction is dated 20 September 2013 and was confirmed on 22 July 2014.

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.

Continue planning

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

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