A new host structure for an early extension by Foster Associates, Gianni Botsford Architects Hampstead home traverses multiple layers of architectural historyThis project was commended in the 2024 AR House awards. Read about the full shortlist hereIn 1967, after the demise of Team 4, Norman Foster set up Foster Associates with Wendy Cheesman, soon joined by Michael Hopkins. Oneof the practices first projects was theremodelling of a 19thcentury coach house tucked behind the carriage archway of a pub in Hampsteads South End Green, north London. Here, with the assistance ofproject architect Patty Hopkins, Foster lent an airy glass vestibule against the oldwalls to the south and sent out anaudaciously modern singlestorey extension to the east. In keeping with the spirit of the project, the Victorian cottage itself was modernismised by Foster Associates inside and out, with new metal framed windows and deornamentation ofdetailing. The house was completed in1968and went on to be lived in and byall accounts enjoyed by the original newspaper editor client for the best partofhalf a century.At the time of this project, Foster was alsoworking on designs for the worlds firstinflatable office building for an earlycomputer tech company in Hemel Hempstead. He was yet to meet Buckminster Fuller or face the American mentors famous question, How much does your building weigh, Mr Foster? But clearly legible in the garden extensions exposed latticework beams, raw blockwork flank walls and floortoceiling sliding windows are the lineages of Team 4s noble shed for Reliance Controls and the concrete, steel and glass house in Cornwall, Creek Vean (both 1965). In turn, the projects influence is traceable in the even more daring and totally seethrough glass architecture of the Hopkins own house round the corner, completed in 1976 nottomention the possibly millions of openplan, bifolddoored kitchen extensions constructed since.Fast forward to 2015, and the extended coach house was sold to a design enthusiast looking for a project, who appointed Londonbased Gianni Botsford Architects after competitive interviews with 10 or sopractices. I think we were the only oneswho did not arrive with a solution, explains Gianni Botsford, whosepractice has a track record of creating unexpected and expressive architecture inurban backland settings such as this, surrounded by other peoples bucolic gardens.Botsford has forged a concreteboned counterweight to Fosters featherlight extensionRetaining the Foster pavilion was alwayspart of the plan, but Botsfords feasibility studies and maquettes went on to explore a range of associated options, including building upwards from the extension andfull or partial retention ofthe original coach house and leanto. Intheend, the decision fell in favour ofdemolishing the lean-to structure and creating an entirely new host structure for the littleknown but historically important early Foster project perhaps not the easiest of architectural propositions.In a strikingly contrasting spirit, Botsfords approach to Reciprocal House owes more to psychogeography than to Fosters systems thinking, taking as it does the starting point of close observation of the experiential qualities ofthis particular hidden enclave of Hampstead, as well as memories of what went here before. The concreteboned counterweight to Fosters featherlight extension forged byBotsford echoes the mansard roof form ofthe Victorian coach house aswell asthe lines of Fosters leanto and is adroitly angled in response to tree canopies, outward views and dozens of potentially overlooking windows. The newwhole is anchored deeply in the earth,perhaps for the next 100 years.It was a little bit jarring, comments Botsford of the original notquite flow between old cottage and Eamesinflected openplan salon. Now, in contrast, a flipped and newly open kitchen and dining zone extends directly from a repositioned entrance, separated from the salon only bya run of kitchen counter and a weir ofthree concrete steps. Apart from the remaining exposed blockwork walls of the Foster extension, the new groundfloor envelope is almost entirely glazed, allowing the surrounding old garden boundary walls and fences, and crowding shrubs and trees,to read as the spaces enclosure bringing textured and shadowy depth of saturated colour to Botsfords recessive, almost ghostly, materiality of fairfaced concrete, aluminium and glass. A terrazzolike floor screed employing thesame local London aggregate as the shuttered concrete of the house provides auniting ground plane throughout the house. As well as relaying and insulating Foster Associates original floor slab, conservation work to the 1968 extension included adding insulation to the roof deck, replacing the original singleglazed windows with a Schuco system and reinforcing the exposedlatticebeams tobring them up to code.Originally completed by Foster Associates for the journalist and editor RonHall in 1968, the first renovation consisted of alean-to vestibule and single-storey extension (below) to an existing 19th-century coach house (above)Credit:Norman Foster Foundation ArchiveCredit: Archive photo courtesy of Gianni Botsford ArchitectsThe two upper floors of the new housestand on the table legs of four squaresection perimeter columns, supporting the slab from which the upper150mm poured concrete walls fold protectively in, as if capturing a moment ofboxing up (or unboxing). Below ground, a snug new basement level of auxiliary living space has been sunk 3m into theearth. This rooted space, with its blockworklined walls referencing Fosters above, is lit by daylight borrowed from lightwells and the mesh surface of the groundfloor car port.With no corridors and an absence ofconventional doors or partition walls, Reciprocal House relies on welljudged spatial zoning for hierarchy and privacy, assisted by banks of bespoke storage and fittings fashioned in finely perforated andtherefore not fully opaque aluminium. Bathrooms and cloakrooms, also odes toaluminium, are stacked by the house entrance to the west of the site a service slice separated via a generous front of house buffer zone of vertical circulation from the increasing seclusion of eastfacing bedrooms and the garden depths of the living space.Holepunched through the sum of thetwo living and two bedroom levels isacircular void through which an allaluminium staircase spirals towards agiant disc of sky. At basement level, thehouses single curtain of felted wool can beemployed to circumnavigate the stair footing for acoustic and visual separation. Usually these days, a stair suchas this would be craned into position as a single sculptural piece, but here accessrestrictions dictated design for assembly onsite, a fact now celebrated inrivets thatexpress the human graft ofsequential assembly.As well as providing daylight, the rain sensorcontrolled lantern is central to Reciprocal Houses passive environmental strategy, balancing stackeffect ventilation, thermalmass heatsinking and heat recovery, with the atmospheric shift that accompanies the opening or closing of oculus instantly palpable. Despite being insome ways theantithesis of systemised architecture, Reciprocal House is undeniably a finely tuned machine forliving in, with its electric glass (fedbyalowvolt current toretain its transparency), automatic blinds and mechanised sliding doors all providing privacy at the flick of a switch. Ithink Norman Foster would approve.Reciprocal House is undeniably a finely tuned machine for living inTo the outside world or at least as glimpsed through the archway on the street or perhaps from neighbouring windows, Reciprocal House presents something of an architectural brain teaser, a total oneoff, calling to mind a chatter ofassociations including mannerism, constructivism, even deconstructivism. The houses angled, oversailing planes ofperforated anodised aluminium, tinted in recessive brown to match the trunks ofadjacent trees, read as partsheltering, partflamboyant. In fact, the expressive sails (or shields or veils depending onyourmindset) serve a dual purpose asrainscreen cladding for the houses mansard concrete sections and as brisesoleil for its leanto glazing, apparently flying in the face of hightechs orthogonal rationality yet at the same timepaying homage to it.How much does your building weigh, MrBotsford? Probably a fair bit. But forall the monolithic concrete, moird aluminium and gizmos, the enduring impression of Reciprocal House remains one of otherworldly dappled light, tree canopies and birdsong.