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AR+D Award 1999: in recognition of excellence
Trees are precious in Africa. They provide shelter for the elders at meeting time, for school children in the midday heat, for all to shield against the unrelenting elements. In a sense the tree has become iconic, almost mythical.
A commission to design a house on the slopes of Table Mountain in Cape Town created an opportunity to test our concerns and searches for contextual responsiveness and connectivity. The site, adjacent to a valley and stream, has a canopy of magnificent spreading umbrella Pines. These trees, majestic and sculptural, provided the primary reference and ultimately the structural concept for the house. Five tree-like structures anchor the roof to the ground and provide shelter for the functions gathered under. These trees are surrounded by an entirely separate lightweight transparent steel and glass enclosure supported on a heavily rusticated stone base.
The design of the house incorporates themes of narrative, of layering and of expressed threshold. The visitor is invited to take part in a journey of discovery, requested to participate in the unlocking of experiences within the house, the unpeeling of layers. We tried to heighten the experience of unveiling and of delicate exposure, to create within the house sensuality and moments of intense intimacy - a folly immersed in, and closely linked with, the majestic beauty of the African landscape - a simultaneous dialogue between inside and outside and outside and inside, neither taking precedent over the other.
Notes from a paper on Tree House
In this paper we have elected to concentrate on a house, namely the Tree House in Higgovale, Cape Town and as a method of accessing the content of the project, we have included a summary of some of influences and themes of our practice, which preceded and naturally informed the design of this building.
It is our firm belief that all projects should be idea or concept based as opposed to being problem solving or stylistic exercises. This position has developed over many years of working together, now almost twenty-five years. We also believe that as designers we should be as aware as possible of the cultural and other influencing baggage that we carry with us, often unknowingly. For if we can understand our influences then perhaps we can build on them and have more understanding of how and why we design in certain ways - be more aware of our options, and design, hopefully with more responsibility.
In the Tree House, the opportunity arose to develop the theme of contextual sensitivity and connectivity. The site, a heavily wooded sloping swath of land adjacent to a valley and stream, is covered with the most beautiful Umbrella Pines, so typical to the Table Mountain slopes. These trees, majestic and sculptural, provided a tantalising reference and ultimately the structural resolution for the house where five tree-like structures which anchor the roof to the ground, provide shelter for the functions gathered under, which in turn are surrounded by a lightweight transparent steel and glass envelope supported on a heavy rusticated base.
In essence the main structural theme of the building is a combination between an ideal modernist plan, where the structure supporting the roof is separated entirely from the enclosure, and an almost classical rationalism in the section - having a base, middle and top. A base acts as a junction between the ground and the steel frame, a heavy brick structure, clad with black slate in horizontal rustication bands accentuating the load of the structure above, the openings measured and deep, with doors retracting into walls and strong, heavy security screens adding an almost mannerist exaggeration to underscore the weight of the base.
The middle two floors are enclosed by the consistent steel crate-like frame, the "shaft" of the structure, which mutates to describe the difference within. For example, on line with the axis of entry, the building sets in slightly to form a shadow. On its northern edge, the frame is filled predominantly with glass infill panels to connect the interior spaces with the outer forest as completely as possible. On the Southern end, however, the steel frame infill panels adapt to become timber, describing and underscoring these as service spaces of the house, a Kitchen a laundry, a service apartment. The timber theme of service is further extended to include timber ventilation panels and a timber-clad fireplace. The uppermost part of the building the, "top", the roof, is structurally entirely separate from the exterior enclosure which is basically self supporting. It is entirely supported by the composite steel and timber Tree-like structures, which carry the load through the house to the ground itself.
The Plan within and the experience of entry are a continuation of the theme of narrative, of layering and of threshold. A lightweight steel bridge transports the visitor from street to 'egg' shaped platform hovering without a clear reference in form to any other aspect of the house. However, it is both separator and connector for the house. It hovers within an opening in the screen wall, which provides necessary west sun control and privacy screening from the adjacent roadway. Within this wall are two urban (sized) doors, the first offering access, the second offering a glimpse of the inner house for the pedestrian. Both these openings are protected by two large sliding screens, the entrance one sliding open from a protective steel mesh enclosure to expose the next bridge to the interior, suspended, with a central band of fish plate with side panels of see through Mentis grating to heighten the experience of suspension. This bridge crosses over a “sloot”, a metaphorical river or moat over which the visitor must pass. It is protected by an over sailing canopy which is suspended not between the screen wall but from the house itself, offering a gesture of hospitality and shelter.
The Front door is large, but glassy and inviting. It admits the visitor onto a series of bridges, which link the two main sides of the house, the living, served spaces and the working, service spaces. These bridges are similar in character to the exterior bridge, still precarious, but include a maple inner lining, a softer, warmer feel underfoot. From this bridge, initially slightly widened for the act of greeting and welcoming, the visitor passes forwards to be faced by a full glass pane framing a view of the magical tree setting, a cylindrical - shaped staircase enclosed in an expanded metal sheath, the bridge toward the visible Lounge / Dining space or a door to the enclosed, private Kitchen space. A curved wall of maple meanders through the Plan metaphorically tracing the run of the river, initially uncoiling from the stair, it traces and defines the functions within the North wing, creating a triple volume space through which the trees are allowed to extend through to the sky to metaphorically photosynthesize. The Lounge and Dining Space extends over the void volume and literally are contained within the shadow of the tree -like canopy.
The tree trunks and branches required a great deal of research and structural analysis, and the process was collaborative at every stage between all members of the design team. In summary, the tree “trunk” is made of two folded GMS plates welded together and bolted to the base and filled with concrete for extra ballast. The connectors between the steel trunk and the timber branches are made of GMS pins which penetrate approximately 200mm into the solid timber branch poles, further strengthened with stainless steel ties to prevent splitting. A universal-type connection at the top of each branch allowed for junctions to the structure wherever best for both structural consistency and spatial effect. In practice the uppermost roof slab, a composite timber crate and lightweight slab needed to be built first on temporary supports after which the branches were connected where after the supports were removed and the roof eased into its position. The Mild steel rods which connect the roof to the structure are necessary tie rods to protect against wind deflection. This separation is deliberately accentuated by the ribbon window of butt jointed glass which surrounds the entire eaves perimeter.
There are two penetrations in the roof itself, a skylight element which is positioned over the central steel and timber spiral staircase and another which allows a further staircase to penetrate up to the roof deck. Both these staircases are strategic elements and are highlighted in order to clarify and describe their function and hierarchical position within the overall structure and design. The central steel stair is a focal one, surrounded by a lightweight sheath of expanded steel it snakes it’s way through all three levels, with maple treads and soft light penetrating down from the uppermost skylight.
The middle level contains the Main Bedroom, Bathroom and a staff flat. The Main Bedroom surround is open and transparent, while the inner wall provides a sheltering edge for the bed and cupboards. Where closure is required internally, the inner walls are glass where possible, sandblasted for privacy. The bathroom has an ample bath and shower which are respectively heavy and light, spatial features rather than appliances in the space. The basins complete the ensemble, light and apparently floating against the delaminated mirrored support. A recess along the edge of the structure provides space for venetian blinds, again timber and horizontal, in sympathy with the timber “service” theme elsewhere in the house.
The structure of the intermediate floors is a grid of structural steel onto which is fastened a permanent shutter of shutterboard, (the very best the Contractor could find), onto which was poured a lightweight concrete slab, for additional acoustic protection. A lightweight timber floor and tiles, where necessary, make up the final layer of this composite lightweight structure.
At the base level, on the "served" side, is located the Study and Guest Bedroom and on the "service" side a Garage, Store and Utility flat. These Rooms have a quite different feel and experience to the upper rooms, being in fact almost in exact juxtaposition. They are enclosed, largely top lit from the void space, and almost like the caves of the building in comparison with the "sitting in the branches of the tree" experience of the uppermost rooms. They also have the added dimension of opening directly onto the garden of the house, the pool and the river.
The Kitchen of the house is located on the uppermost floor adjacent to the Lounge and Dining Room in the timber clad service side of the building. It too shelters under the canopy of a single structural tree and the cupboard fittings are maintained at a low height to allow the ribbon window to continue through unobstructed. Brushed stainless steel surfaces blend with the timber, glass and porcelain tiled surfaces. The Fireplace similarly timber clad on the exterior "floats" in the east glazed wall in order to least obstruct the view. A beaded stainless steel cupboard door screens a storage alcove adjacent internally to the fireplace.
The house has it's own particular way of responding to the surrounding environment and with the prevailing climate. The large Pines and Poplars, not indigenous, but nevertheless now well established on the Cape skyline, provide it with natural shading devices, and a soft penetrating dappled shade. The solid brick west wall stands separate from the glass and interrupts all low west sun before in can penetrate the building. The triple volume also acts as an exhaust for air, cool air being drawn over the pool, through the ground floor slot vents and grilled openings, and through to the upper spaces. Being located in a sheltered valley the site rarely experiences strong winds, while laminated glass and internal blinds further protect against excessive temperature variations in both summer and winter.
As with our previous projects it is evident that the narrative remains a central theme in the Tree House, the visitor being invited to take part in a "journey of discovery" to unlock the elements within the house, to unpeel the layers, as Mathew Barac has described in the Architectural Review, rather like a "Designer Onion". In many ways we tried to heighten the experience of unveiling and delicate exposure, to create within the house sensuality and moments of intense intimacy.
All truncated references not fully cited below are those of Joanna Walker's original text and cited in full in the 'Bibliography' entry of the Lexicon.
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