House Extensions in Hampstead (NW3)

Much of NW3 has lost more permitted development than the national conservation-area rules take away, and the extra controls sit mostly at the front of the house.

The Hampstead conservation area. Designated in 1968, it covers the old village and its surroundings on the edge of the Heath. Article 4 directions have applied to houses in it since September 2010, and in June 2025 Camden made a replacement direction for the whole conservation area except Frognal Way, which has directions of its own. The new direction takes the street-facing side of the house out of permitted development: extensions and alterations to the front, and to any side wall facing a road; changes to the front roof slope; porches; paving at the front or side; chimneys and flues visible from the street; front walls, gates and fences, including taking them down; and painting the front of a house that isn't already painted. The one thing it drops from the 2010 version is solar panels, which Camden wanted to make easier to fit. Camden said the direction would come into force in June 2026 if confirmed, and planning.data.gov.uk now lists it from 9 June 2026.

Fitzjohns/Netherhall. This conservation area, designated in 1985, got a newer and narrower direction at the same time, aimed at front gardens: paving over a front or side garden that faces the street, putting up or altering front walls, gates and fences, and demolishing them. Camden's reason was the appraisals it adopted in December 2022, which found that lost walls and hedges and front gardens paved for parking were eroding the green character of these streets. Redington Frognal, the conservation area across much of Frognal ward, has the same front-garden direction, and planning.data.gov.uk lists both from 9 June 2026 too.

What they don't touch is the back of the house. A rear extension out of sight of the street is governed by the national rules for conservation areas: a single-storey rear extension within the standard 3m or 4m can still be permitted development, but side extensions, the larger-home prior-approval route, dormers and other roof enlargements need planning permission, and a listed house needs Listed Building Consent whatever the size. In practice the front of a Hampstead house now gets planned with the extension rather than after it: bins, bikes, parking and the boundary wall go in the same drawings.

Most of Belsize Park falls in Camden's Belsize ward, one of the three wards in the decisions above, and nearly all of that ward lies in conservation areas: the Belsize conservation area, designated in 1988, covers most of it, and Fitzjohns/Netherhall takes in the north-western side. The houses are big Victorian villas and terraces, many of them long since divided into flats, and that changes the question before any design starts. A flat has no permitted development rights, so a garden-flat extension, a lower-ground dig or a roof addition on a converted house is a planning application every time, with the freeholder's consent under the lease as well.

The Belsize conservation area has had Article 4 directions on particular houses since 2010, and a separate direction from 1994 covers a run of houses on Belsize Avenue. In June 2025 Camden made a replacement direction for the conservation area on the same terms as Hampstead's, bringing the street-facing side of the house into planning and letting solar panels back out, and planning.data.gov.uk lists it from 9 June 2026. The basement direction applies here as it does across the borough.

With the front of the house controlled, the space to gain in Belsize Park is at the back and below: a lower-ground floor opened to the garden, or a rear extension at garden level, with the street elevation left as it is. That's where the rules leave room, and it's where we start the design.

Camden's Policy A5 sets the envelope for a Hampstead basement before design starts: one storey, less than one and a half times the footprint of the house, and no further under the garden than half the garden's depth. The Basement Impact Assessment that goes in with the application is normally checked by an independent engineer at the applicant's cost, and it has to show no more than very slight damage to the houses either side. Camden's guidance also names Hampstead Town among the parts of the borough at higher risk of surface water flooding, so the drainage and a pumped outlet are designed early. Approvals do come through: in the twelve months to 22 September 2026 Camden approved basement schemes on Lower Terrace, Lyndhurst Road and Pilgrim's Lane in Hampstead Town ward, and on Glenmore Road and Lancaster Grove in Belsize. For how the dig, underpinning and waterproofing are done, and what a basement typically costs in London, see basement conversions in North London.

Plenty of Hampstead projects are not extensions at all so much as reinventions: a listed or conservation-constrained house rethought floor by floor, with a basement doing the quiet heavy lifting and a garden-side addition finishing the composition. At NW3 values that programme rewards real design, and it is priced as one fixed figure however far it runs.

We run that scale of work through our luxury extensions service, one team from heritage drawings to handover, with the budget bands laid out plainly in the luxury extension cost guide.