In Vienna, near the Westbahnhof, at the highest point of Felberstraße, a two-storey rooftop extension has been added to a late nineteenth-century house. In a fully built-up area where it it is hard to find any additional residential volume, the architects Regina M. Lettner and Günter Lagler of skywood by baukult set a new two-storey space on top of the existing building. The rooftop extension, called ‘Bird of Paradise’, is an example of excellence in urban densification, in terms of cost-effectiveness, ecology and adding value to the property. Lightweight and quick construction is often the key to success with extension projects, and this makes special demands on planning and materials. Here, the architect and owner skilfully used the light and high-performance materials wood and steel, which gave her the most freedom with the design while respecting the existing structure. The extension is made mainly of prefabricated wooden elements with some steel. The structure is exposed and visible in the interior, making an architectural statement. The wide-span Kielsteg elements form the roof structure and set new standards for urban wooden building by reducing the load on the substructure and creating pillar-free floor plans. The roof is partly green and partly covered in photovoltaic panels. After only five weeks in construction, the new living space is inviting, spacious, open and full of light, with fantastic views into the far distance. Wherever the existing structures and the planning regulations allow, this type of rooftop extension in wooden construction offers the perspective of activating valuable and much-needed reserves of urban living space with a low CO2 profile.