'We like the natural daylight effect,' says Martin MacKenna of Fraser Brown MacKenna of the 'very rich shading' that comes from incisions in an otherwise homogenous and uniformly coloured surface. 'It's very three-dimensional.' His firm's penchant is immediately obvious in the top right-hand corner of a large, white, square wall which has The Automobile Association's familiar logo 'aa' inscribed into it in 25mm-thick Stoboard. With the sun picking out the letters, it is just as visible as the distinctive black-on-yellow, yet has the advantage, says David Bramma of the aa's Property Division, of not bringing members of the public flocking to it to have their cars fixed. For this is not a public facility but the aa's National Technical Centre on a business park outside Basingstoke, and the interplay of relief and light to create shadow is a theme the architect carries through to the interior in its careful amalgamation of existing and new steelwork.
The giant square has another function than to establish the aa's presence. It is also a gesture large enough to disguise some of the crudities of the 1574m2 standard industrial shed which lies behind it, and a vast improvement on the shabby block which it replaces and which provided the previous entrance and offices for the facility.
MacKenna dates the original industrial shed to the 1950s. For some time the aa had occupied it as an engineerig research facility where products were tested and developed for use by the Patrol force. At some point it spawned an entrance lobby that job architect Kathryn Dunk calls a 'spandrel panel arrangement' on two storeys, with dark-brown glass spandrel panels up to sill level on each floor and aa stickers in the windows either side of the unprepossessing entrance door and small lobby. In turn it also offered inadequate office space to house the aa's Technical Library, and when the vehicle testing team was moved to be closer to its engineering colleagues, the opportunity arose to convert the workshop area to house the library and its support team. The Project Managers, Spicer Partnership, recommended Fraser Brown MacKenna, and, as Bramma says, 'we liked what they had been doing'.
For the aa, Bramma explains, the technical library was the crucial part of the project. The organisation was concerned, he says, that 'it would be in an enclosed space, without natural light', but fbm's design, with increased ceiling height, coloured walls and floor finish, is 'popular with its occupants'. With the new library, the building's working population has increased from 31 to 54.
The entrance is scarcely less important. 'We wanted to improve the front office space and frontage,' says Bramma. But the budget of £350,000 was very low. This meant re-using as much of the existing structure and foundations as possible, a contingency which meshed well with fbm's aesthetic principles. 'To be honest,' expands MacKenna, 'I quite enjoy the idea that if we have a bolt holding something up, we like to show it.'
He admires architects like Mies and Miralles, whose steelwork he finds 'very elemental but also wild'. And he enjoys the idea of a steel fabrication standing within a larger overall volume, allowing the whole space to remain apparent. Not afraid of the idea of re-using an existing component in accordance with this almost Arts and Crafts, spab-inspired vein, the architect even found potential in the existing steel frame of the office extension. As bland as it could be, once stripped of its fire-protective casing it had a certain elemental quality. With the large white wall forming an extension around the line of the original corner, the existing column became a feature within the newly created and expanded reception area. Elsewhere, the shabby original walling is replaced by a simple curtain walling system. As the gaps between the previous edge of the building and the new white wall are all glazed, the space captures a lot of light from different directions, just right to show off the relief of the channels and protruding bolts.
The original structure was never meant to be visible nor to form the edge of a gallery overlooking the reception desk and leading to the first- floor offices. It required a handrail and new steel angles to hold it. While many architects might have been tempted to create a clear distance between old and new - and, indeed, to choose the more usual wood as a finish at least to the top rail of the balustrade - fbm has opted instead for steel. It devised two details. One connects the new handrail to the existing steel beam on the landing at the top of the stairs which leads to the new 'balcony' in space created by the expansion of the building between the inside of the white wall and the original building line which looks one way to the entrance and the other across the front of the building. Here a new 178mm x 76mm rsj spans from the original corner column to the white wall. Two steel angles were fixed to it: one, 60mm x 60mm, is continuously welded to its back as fitting for the floor joists; the other, 75mm, x 75mm, sits above and oversailing the rsj to which it is intermittently welded. It holds the handrail and floor finish consisting of 22mm Junckers boards.
Within the line of the original building, fbm retained the existing concrete floor structure. But a new angle holds the handrail similar to the one for the balcony. In front of these angles stands the handrail. It is a simple, welded fabrication of steel flats, 50mm x 15mm for the uprights, 50mm x 10mm for the horizontals, the top one having a 30mm x 10mm flat welded to its underside to stiffen it. All is coated with a silver-grey metallic paint - undercoated with a primer or intumescent paint where fire protection was needed - to give both old and new a homogeneous feel. Traces of a previous life in the existing steelwork, though, are apparent in the unfilled holes where fixings were attached to the corner column.
Two fabricators worked on this installation, Cowcher Fabrication and Mid Kent Steel. A third, Albion, made an external spiral staircase which acts as a fire escape from the first-floor offices. Here cost limits forced re-use of existing steelwork. Care and thought in the design process made it reusable as part of an overall steel-based aesthetic.