Ifyour head office is a dull brick '50s block in the south London suburb of Tooting, new work can afford to be radical.Wandle Housing Association occupies what was once an Inland Revenue office - concrete and steel frame clad with brick, a flat roof, and a single storey flat-roofed office addition running along the north and west sides. A few years ago the association commissioned PRP Architects to rethink the entrance lobby and reception. Visitors now approach the entrance via an aluminium and stainless steel ramp; they pass through automatic sliding glass doors and into a glass lobby with a blue glass roof supported on glass rafters; this leads, through a widened opening, to the new reception area. The new lobby increases the depth and quality of daylight and gives the association a modern image.
Inspired by this, the association was keen that the next phase, more administration office space, related to the modern concept and materials of the lobby. But project architect at PRP Richard Pain left to set up his own practice and the new phase has been designed by PRP with pain + phillips architects.
The original idea, to put another storey on top of the single-storey office on the north and west sides of the two-storey building, was limited by planning restrictions to the north side of the building only.
The first-floor extension has a curved roof which extends 1.5m beyond the walls of the single-storey office to give more space and rises to oversail the original parapet wall of the two-storey office, incorporating a row of clerestory rooflights which flood the new space with sunlight. The roof is clad with pre-patinated zinc with standing seams. The west gable wall is also clad with pre-patinated zinc, laid in diamond-shaped 'fish-scale' panels. A fully-glazed south elevation is set back from the original parapet to create a terrace, protected by a glazed balustrade.
The structure of the new extension, a series of paired glulam beams flitched to curved steel beams, is fixed to the face of the ground floor external wall and leans outwards before curving back to land on steel posts about 1m above the existing upper floor roof. At upper levels the wall - an insulated lightweight steel-frame system - rests on the glulam beams; at lower levels it is suspended from an RSA beam bolted to the curved flitch plates. Timber windows, clad with silver anodized aluminium, face the blank gable of an adjacent house or are obscured where privacy of the house at the back of the site might have been infringed.
The window openings of the first floor offices are retained as an open screen and their concrete surround is reflected in a new dry-lined border in which the border is painted white against the background of the orange painted wall, matching the Wandle Housing Association's orange logo.
The new terrace at the front has a structural glass balustrade in the same blue laminated glass that forms the roof of the lobby; it is capped with an aluminium-cored stainless steel handrail. Likewise the same aluminium decking used for the lobby ramp forms the terrace floor and the landing and treads of the galvanised fire escape staircase which leads from the new office.
The new extension cost £175,000; it provides desk space for six extra staff and a space for meetings.