Major refurbishment and extension of an Edwardian house with addition of a Passivhaus-standard annexe in south west London
Set in a conservation area of Kingston-upon-Thames, this project has seen the reworking and extending of a double-fronted detached Edwardian Villa and rebuilding of its poorly constructed 1970s bungalow annexe to create flexible live/work accommodation for the architect Stephen Coates and his wife Andrea.
The original villa was stripped back to a shell, with only the timber stair at its centre retained, a large living/kitchen extension built to the rear and double-glazed heritage windows, thermal insulation, air source heat pump air conditioning and underfloor heating installed.
With grown-up children, the couple wanted the house to be able to accommodate visiting family but not feel empty, or have unused bedrooms, the rest of the time. So on the first floor, four bedrooms have been worked together to form a main bedroom suite, with dressing room and snug. Hidden beds in the study, snug and a bedroom in the annexe accommodate the couple’s extended family of nine as and when required.
Source: Stephen Coates
The heart of the composition is the courtyard garden sitting between the main house and the annexe, designed around a acer tree discovered during clearance of the garden.
The new-build annexe is constructed of prefabricated structural insulated panels (SIP), erected in one week, which have been waterproofed and clad in fire-treated and black-stained Siberian Larch from a sustainable source in Scotland. It is designed to be used as an office, studio, gym or family/guest bungalow.
Throughout triple-glazing combines with high levels of insulation and airtightness to ensure low energy use. 50% of all power needs of the house and annexe are met during daylight hours by an array of 18 solar panels sitting on the annexe roof.
Source: Stephen Coates
The design of the courtyard garden was developed, working with Tom Howard, around a beautiful acer tree discovered during clearance of previous overgrowth. The tree is visible upon entry to the villa and defines a path through the house to the annexe, partly hidden behind the ‘folded plate’ wall which frames the acer and acts as the fourth wall of the living space.
The extension is finished in matching brick but with a floating concrete slab that takes its cues from the white lintels seen on the front façade of the villa. Off black walls and insitu concrete floors extend from the hall, through the living / kitchen space into the garden and link and identify the new interventions.
Source: Stephen Coates
In the villa, rejecting a stripped back interior of white walls and shadow gaps, replacement period detailing was re-introduced including skirtings, cornices, architraves, new timber floors and new double glazed heritage windows. Roof-lights were introduced above the stair and master shower to reduce need for artificial light at the centre of the square plan.
As the kitchen shares space with the living area it was designed as ‘boardroom’ furniture – dark stained timber, black granite offset by an oversized extractor finished in etched stainless steel. The kitchen is supported by a utility kitchen that sits between the open kitchen and dining room.
The form of the replacement annexe was defined by the existing floor slab which had to be retained to avoid disturbing roots of neighbouring trees. Prefabricated structural insulated panels (SIP)-erected in one week - offered unparalleled speed, levels of insulation and crucially, weight savings and a spread loading on the retained perimeter strip footings.
The SIP panels were wrapped in breather paper and waterproof ply on battens. The whole enclosure was then wrapped in single ply waterproof membrane with proprietary fixings that allowed timber support battens to be connected through the waterproofing. Further battens support the external cladding of fire treated and black stained Siberian Larch from a sustainable source in Scotland.
Stephen Coates, aCTa
01 site plan page 001 2
Source: Stephen Coates, aCTa
Start on site September 2018
Completion date December 2019
Gross internal floor area House 320m²; Annexe 110m² (incl. garage)
Construction cost House £960,000; Annexe £275,000
Architect and interior design Stephen Coates, aCTa
Client Stephen and Andrea Coates
Structural engineer Blue Engineering
Lighting Lucy Martin
Landscape consultant Tom Howard at www.tomhowardgardens.co.uk and Stephen Coates
AV consultant HiTech homes
Project manager Stephen and Andrea Coates
Approved building inspector Marc Rees, London Borough Hammersmith and Fulham
Main contractor Huser Design and Build Ltd
CAD software used Autocad 2020