Rooftop Extension in Stuttgart
The elevated region of Stuttgart at the boundary of the forests with the vineyards, which reaches as far as the inner city on the floor of the valley basin, is a sought-after residential area offering a magnificent view. The apartment building had been built with restricted resources in the 1950s. To be able to erect a penthouse with a roof terrace on top of it, a close eye had to be kept on low weight in the choice of materials and construction. The project comprised renovation of the building and the balcony, in which the plaster was entirely removed and replaced with coloured scraped rendering, and replacement of the railings. To create another floor it was necessary to remove the uninsulated hipped roof. The first two floors of the property consist of one-room apartments accessed via pergolas, and feature a bulkhead structure on a 3.35 m grid. The existing second floor can be functionally incorporated with the roof apartment as an optional additional area, or may be used separately as an office. The new, external spiral staircase provides access to the office and the roof apartment, separate from the existing apartments. The floor plan of the glass superstructure results from the architects’ desire for a floating stage. This had to be harmonised with the necessary clearance areas and the planning authority‘s requirement for a staggered story. The all-round glazing gives the impression of an open roof terrace, even from inside. The sloping situation leaves little opportunity for being overlooked. Six external sliding doors of untreated aluminium, 1.90 m wide, provide access to the outside without sills, and ensure adequate cross-ventilation. The lightweight structure can therefore be cooled quickly in summer. Controlled ventilation prevents heat loss through the openings in winter. The minimal structure, having the lowest possible weight, is constructed from wrought industrial products. The facade pillars simultaneously support the roof. The underside of the roof consists of trapezoidal corrugated sheet spanning more than 6 m. Fastening the 75 cm wide panels with high shearing-strength rivets at the abutments creates a stiff horizontal roof plate supported all round by an L-shaped edge beam.
