The original building, a freestanding six storey apartment block in loadbearing masonry construction was built in the early 1960s. The building comprised 24 apartments, and remained almost fully occupied throughout the development. The client bought an existing 1,600 sq ft ‘penthouse’ which had been constructed over part of the flat roof of the existing building in the 1980s, and had established rights of access to the full extent of the remaining flat roof. The existing penthouse was poorly conceived and cheaply constructed, occupying the spaces in between existing tank rooms and lift over-runs and accessed from the passenger lift on the floor below. A planning application was submitted and negotiated for a pair of two storey duplex apartments with a series of terraces and external areas. Each apartment was entered by direct lift access to the seventh floor where the living accommodation was arranged, from where a sweeping top lit helical staircase connected to the bedrooms and private quarters on the sixth floor below. Though broadly mirrored to each other, the existing layout of the fifth floor required that the two apartments were slightly different in layout, each one offering four bedrooms with ensuite bathrooms, generous living rooms, high spec kitchens and formal dining rooms. The majority of rooms have access to lushly planted private terraces, the largest of these reserved for the living rooms which are located on the quieter side of the building away from Finchley Road, and orientated towards views to Primrose Hill and the lights of the City in the distance. As construction started on site a further planning application was submitted for an eighth floor, which consisted of a sun room and further terrace sunk into the roof form. This was to benefit the northern apartment, which had less favourable views towards the south. Eventually won on planning appeal, this variation to the contract was absorbed into the main contract works. Where appropriate prefabricated techniques were employed to minimize time on site, disruption and noise. The main new structure was designed in KLH solid timber floor and wall panels on a steel grid to transfer loads onto the loadbearing walls below. A particular technical challenge was to keep a lift service operating throughout the construction period, while shutting down and extending first one lift shaft and then the other; the second of which was to be converted from a basic goods lift into a part M compliant passenger lift in the process. External finishes comprised an insulated render system and copper roof and wall cladding, these being artfully composed to break up the apparent bulk of the new accommodation while visually linking it to the rendered plinth level at the ground floor. The interiors were decorated to a high quality finish by others. Total floor area of the new development was 7,000 sq ft.