Springfield Avenue

• LOCATION: N10, London
• PROJECT: Refurbishment with ground floor and basement extension
• CLIENT: Marianne Davys
• ARCHITECT: Marianne Davys Architects
• STRUCTURAL ENGINEER: Charles Harris & Partners
• PARTYWALL SURVEYOR: James Davidson
• CONTRACTOR: Domi Development
• CONSTRUCTION COST: £200,000 + VAT
• CONTRACT: JCT Minor Works Building Contract
• DATE COMPLETED: 2015

Project brief

The property is a 1950s semi-detached ex-council house with gardens to the front and rear. The house is at the end of a cul-de-sac on a south-facing sloping site, next to Alexandra Palace and with panoramic views of London.

The brief was to provide a self-contained studio basement extension at ground-floor level, to alter and extend the ground floor of the property using the roof of the basement extension as a terrace outside the new kitchen and dining areas, and to provide a roof terrace at first-floor level accessed from the master bedroom.

Project specifics

A public sewer running behind the house had to be avoided, so the new basement is two metres away from the footprint of the original house.

Although the slope reduced the amount of excavation needed to the basement, this was still a significant exercise. An excavator at garden level did most of the digging, and two separate conveyor belts carried the dense clay to a compound at street level, from where it was removed daily over a period of five weeks. The excavator then exited the garden via a purpose-made ramp to the council-owned allotments to the rear of the property.

By establishing the existing water table level and using the natural slope of the land, there was no need for pumped surface water drainage. Surface water in the rear garden is taken to a soakaway under the lawn.

Apart from maximising enjoyment of the sun and the views, the benefit of the roof terrace at first floor level is its function as an alternative means of escape that enables a more open-plan arrangement on the ground floor.

The ground-floor extension with a sedum roof is highly insulated, and the original ground-floor structure was replaced with new insulation and underfloor heating, so although the house has increased in area by one-third the heating bills have increased by a relatively smaller amount. Good relations with neighbours were crucial and all were patient and understanding about the temporary loss of parking, the noise and dust, and the daily deliveries of materials. An almost identical project was carried out for the adjoining owners.

Project challenges

• Obtaining planning permission for roof terraces.
• Access for the excavator and removal of the waste material to street level with a series of conveyor belts.
• To meet the fire regulations, given the open-plan internal layout.
• To provide the new basement accommodation at garden level without the need for pumps.
• To design around a public sewer that ran behind the original house.
• The architect was living and working in the house during construction and the loft-level office looks straight down on the site – a challenge for the contractor!