Extension to Architectural Office Lausanne

Maria + Bernhard Zurbuchen-Henz

Subject | Extensions to buildings can be approached and designed in different ways. They can either match the style and material of the existing building, merely only altering its size, or they can intentionally deviate in terms of style and material, thereby expressing something new and leaving the nature and size of the original structure untouched. Here, the second approach was chosen and implemented in a convincing fashion.

Design | The house belonging to the architects Maria and Bernhard Zurbuchen-Henz is located on the edge of the city of Lausanne, in a district with a mixture of different building styles consisting of housing blocks and small detached houses with garden sheds. This theme was taken up by the architects as they started planning their office extension in 1989; the project was completed in 1991. The new lightweight wooden pavilion represents a functional but informal extension to the original detached home. The simple design is a skilful answer to the existing circumstances, such as the narrow plot, the lush vegetation and the heterogeneous surroundings. Owing to the distances to the boundaries which had to be maintained, the new structure had to be built in the middle of the plot. Therefore, the garden was subdivided into different sections: front garden, back garden and patio. The front garden is used exclusively by the office, the rear part is private and the patio serves as a direct external extension of the house. The banal detached house dating from the 1930s and converted as long ago as 1964, is clearly improved by the addition of this extension.

The architects chose timber as their building material because, due to its un-pretentiousness, it best satisfied the nature and scale of the project. In addition to that, the extension had to be completed quickly and on a low budget. The result was a formally modest but very skilfully designed structure.

Location

Maria and Bernhard Zurbuchen-Henz, Ch. de Maillefer 19,1018 Lausanne, Switzerland

Client and Architect Maria and Bernhard Zurbuchen-Henz, Architectes FAS/SIA, Lausanne Project Architect Claire Bertusi

Structural Engineer Jean-Pierre Marmier, Ing. EPUL/SIA, Lausanne

Timber Construction Mullener SA, Pully

Date of Completion 1991

Costs

The total cost of the works was 180 000 Swiss Francs. For a volume of 325 m3 that equates to 376 Swiss Francs per m3, and for a usable space of 109 m2, a cost of i i2i Swiss Francs per m2.

Structure | The building not only exhibits wood both inside and outside - it is also conceived as a timber-framed structure. The two-storey pavilion in the garden, with meeting room downstairs and private accommodation upstairs, is placed at the end of the single-storey office wing. The complete extension rests

7 | Detail of window, scale i:io.The window frames for the opening lights are screwed directly behind the structural members and include a silicone seal. The fixed lights lie in the plane of the air space and are attached to the timber members from the outside.

6 | Detail, scale 1:20. The air gap on the outside of the thermal insulation is very neatly planned in the roof and wall constructions. The vapour barrier is on the inside in front of the thermal insulation and directly behind the internal plywood cladding. Roof construction: 50 mm gravel, synthetic roofing felt, 22 mm plywood, 160 mm air space, 120 mm thermal insulation, 15 mm plywood ceiling. Rooftop patio construction: 27 x 160 mm wooden open-grid flooring, 40 x 60 mm battens, 20 mm plastic spacer blocks, 3 mm protective layer, synthetic roofing felt, separating layer, 22 mm plywood, 160 mm air space, 120 mm thermal insulation, 15 mm plywood ceiling. Wall construction: 24 x 80 mm external cladding, 30 x 60 mm air space, protective layer, 120 mm thermal insulation, vapour barrier (airtight lining), 15 mm plywood internal cladding.

8 | The two-storey pavilion from the west. The stairs lead from the rooftop patio down to the private part of the garden.

on a concrete plinth which raises the timber construction about 400 mm above ground level and hence protects it from splashes of water. The timber frame consists of 60 x 120 mm studs at 80 cm centres and of 280 x 60 mm floor and roof beams. All the structural timbers, such as columns, header/footer joists and beams, are glulam members. Stability is achieved by way of the 15-mm-thick plywood panels which remain exposed internally.

The thermal insulation is placed in the bays between the beams and consists of 120-mm-thick rockwool batts.The roof of the pavilion, a cold roof like the office wing, has a 150 mm ventilation space between thermal insulation and roof covering. The roof covering itself is made up of 22 mm plywood covered with a synthetic roofing felt. The roof of the pavilion includes a 50-mm-thick layer of gravel on top of the felt for protection. In the case of the patio, battens on spacer pieces are used to support the wooden open-grid flooring above the roofing felt. The external walls have open-joint boarding ventilated from behind consisting of 24 x 80 mm douglas fir planks. None of the timber has been treated in any way; it retains its natural colour and will change with time accordingly. The only metal to be seen externally is in the form of the hot-dip galvanized steel posts for the balustrading around the patio. When asked "Why metal here?" the architects replied: "We wanted to have a clearly defined volume made of timber, all other elements are only implied and form only apparent spatial boundaries."

8 | The two-storey pavilion from the west. The stairs lead from the rooftop patio down to the private part of the garden.

9 | The pavilion during construction. The necessary bracing is attached on the outside so that the plywood providing the permanent stiffening can be screwed on later from inside the framing.
10 | Simple external corner detail for the boarding. Visible here are the open joints and the shaping to deflect the rain. The horizontal external corners of the planks are at the same height, conveying the impression of continuous strips.
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