The owners first wanted to demolish and build bigger; instead KOSMOS Architects and Gordon Selbach gave a 1972 Vienna villa a second life as Stammhaus, a house that can hold three households under one roof.
In Wolfersberg, a quarter in Vienna's 14th district, private homes sit close in compact gardens, most built between the 1960s and the 1980s. Johann Bachl put up this single-family house in 1972, one of many caught between housing demand and pressure to densify. KOSMOS Architects and Gordon Selbach took the opposite view. "Houses from this period are frequently undervalued," KOSMOS notes, and demolition wastes the material and carbon already locked into them.
The clients, a couple with two teenage sons, had wanted to maximise floor area; instead the house was reorganised from within. "A new roof unifies and gathers the volumes of the existing 1970s villa into a single, simple form," KOSMOS writes. Its higher pitch is extended toward the garden, and it partly shelters the terrace below.
Strategic cuts through the facade, walls, floor slabs and roof open the once-dark, labyrinthine plan into rooms that join or split as the family changes. Each bay between the load-bearing walls now draws light and cross-ventilation from both street and garden, organised in an enfilade like a Viennese Altbau. On the lower level, almost buried as the ground rises to the garden, the soil was cut back, turning 70 square metres of dark, underused area into living space with direct garden access and a new street entrance.
The house can live as one dwelling or divide into three. Reading the structure as three blocks across three floors, KOSMOS and Selbach treat the vertical circulation as a free-standing core, a spine that lets air and light through while discreetly dividing the main living areas and forming in-between spaces from which toilets and storage are reached. Three terraces grade the privacy: a main one under the extended roof, reached by amphitheatre-like steps from the garden; a second embedded in the garden by excavation, set deeper within the greenery; a third from an opening in the roof, oriented to the opposite side of the site for visual and acoustic privacy.
Budget and speed ruled out bespoke detailing, so the palette leans on standard industrial products. All visible load-bearing timber is painted green, a nod to Otto Wagner's green across Vienna and to the lacquered wood of Adolf Loos. Walkable surfaces are laid in herringbone parquet; polished metal wraps the circulation core and the kitchen; the roof is clad in Prefa aluminium shingles ordered without their colour coating, so it catches the light and alters as the weather turns. Even the plaster facade carries a little silver pigment, enough to shift with the angle of view and change with weather and season.
The whole transformation took a year and a half, at EUR 1,650 per square metre, showing reuse can be quick, low in cost and green. The clients had insisted they never watched television and wanted no set. The first object to arrive, before any furniture, was a large screen, and the house's interconnected spaces absorbed the rearrangement easily, joining or separating as needed.
