This two-storey house extension in Wohlen, AG, Switzerland is the result of three years of close collaboration between our two architecture offices, Gwendoline Eveillard Architecture and bürodrü, and with the engineers Schnetzer & Puskas.
Built in the 1950s, the existing house extends over two levels and follows a typical layout of that era. Rather than demolishing and reconfiguring the interior, we chose to add a complementary structure—a shell of the same size capable of accommodating all the functions that could not fit within the existing space.
The extension completes the existing house by creating a long-missing link between the interior living spaces and the garden. It serves as a counterpart to the original structure, replicating its volume with the same dimensions but in an interactive and evolving form—transparent and reflective, adaptable and adjustable. This project is a reflection on flexible functionality, structure, and processes of construction.
Throughout the design process, this project has become a demonstration of how a structural system can serve not only its load-bearing purpose but also act as the solid backbone of a flexible, evolving, multi-purpose space - shaping and defining it while still allowing maximum adaptability.
The new hybrid steel–concrete–timber structure is organized around four columns arranged on a 5 × 5 m rectangular grid.
All columns are positioned within the interior, near the perimeter of the ground floor. The steel structure above follows the same 5 × 5 m grid and consists of IPE 160 beams supporting a 16 cm raw concrete slab, together forming a composite construction. On the south and east sides, the beams cantilever 2 m, creating an interior first-floor footprint of 7 × 7 m. In these same directions, the cantilevers continue outward as balconies. Above, the structural logic repeats as a roof grid of purlins and rafters, topped with prefabricated timber hollow-box elements.
The extension functions statically independent of the existing house.
The project’s character arises from the interplay of its vertical and horizontal structural elements, which actively shape the interior spatial experience. The steel connections were custom-designed to allow most elements to be pre-welded, enabling on-site assembly with a minimal number of screws. Each of the four columns was individually selected or engineered to meet its specific structural requirements with minimal material use. The steel structure was erected in just two days. Its design allows for straightforward disassembly, creating the possibility of relocating the house in the future or modifying the façade without requiring structural alterations.
A fully glazed façade wraps around the space. On the ground floor, retractable façades create a seamless transition between the garden and the living area.
On the upper floor, non-load-bearing partitions and the framework are made of wood. In both its layout and symmetrical design, the house aims to be flexible and multifunctional, closely connected to the outdoors through its transparency and openings.
