Apt turns to prefabricated pods to extend a listed modernist house


Designed by Erich Mendelsohn and Serge Chermayeff for the publisher Denis Cohen, 64 Old Church Street was completed in 1936 and is one one the most significant Modern Movement houses in the UK. The grade-II*-listed Chelsea house has been in the same family ownership for 40 years, and has recently undergone its second major modification. The first – which included a new conservatory at the south end – was completed in 1992 by Norman Foster, who had been taught by Chermayeff at Yale. The second is by Apt, and comprises the refurbishment of the exterior and a new extension at the north end of the building providing staff accommodation.

The structure of the original house is a steel frame with a cement-rendered brick skin. The roof is a combination of steel and hollow tile. “Extensive research was carried out to match original finishes and details as far as possible”, says the architect. “Architecturally this included window rhythm and proportion, providing natural top-lit space and matching exterior paint finishes and colours”.


In the original building, honey-coloured sycamore and pear wood panelling were used to line the living spaces, and form niches, shelving and fitted wardrobes that are still in use. “Key details were replicated and materials matched”, says the architect, “including the source and nature of timber veneers, door handles – cast using the originals for moulds – light switches, paint finishes, window frame ironmongery and up-lighting”.

The new extension is designed to be easily removable to allow restoration of the house to its existing condition at some later date, and was prefabricated to minimise disruption to the house and its occupants, and to afford a high degree of control over the quality of finish.

Intended to complement the existing architecture, the addition follows its tripartite vertical division and the proportions of the glazing, but maintains the building’s asymmetry, and makes a clear distinction between old and new.


The open-plan space has three zones – kitchen, dining, and living – sitting under a series of vaulted ceilings, which could be constructed from three prefabricated modular pods. These came to site largely complete, with services and fixed joinery already in place.


The design of the pods was developed with structural engineer Expedition Engineering and fabricator Weber Industries, and their installation was “meticulously planned over several months, including the commissioning of a point cloud survey which would serve to assist the extension’s integration with the listed building fabric”, says the architect. The pods sit on an independent structural frame spanning between the garage wall and the existing house, so all preparatory work could be completed in advance without major disruption. The three units were delivered to site and lifted by crane over an eight-hour period, before being bolted into position and sealed to each other and the existing house.

“64 Old Church Street is a wonderful example of how off-site construction techniques can be utilised to create a sensitive addition to a much-admired heritage building”, says Apt’s James Ewen, “retaining the building’s character whilst also ensuring that it is suitable for modern day living”.