First, the tapered column heads were inserted into glued laminated timber downstand beams. Then, cross laminated timber ceiling slabs were set on top of them. The carpentry-style connections resemble traditional Japanese wood construction. In follow, 25 mm thick and 330 mm long beech dowels were hammered into pre-drilled holes in the downstand beams. Wall and ceiling panels consisting of cross laminated timber were connected with x-shaped birch plywood dowels along their butt joints. This was the first time they were used in Norway in this manner. The timber frame facade elements were manufactured in the workshop and clad with prefabricated, shingle-covered elements on site. They were chosen to echo the small scale brick structure of the neighbouring historic storage building. The inclined window reveals feature fabric sun blinds in pastel green hues, corresponding to the climbing plants on the open emergency stairwell facade oriented to the street.
60 % of furniture pieces, sanitary objects, ventilation systems, raised floors, and acoustic panels were sourced from upcycled items from other buildings. The remaining 40 % consist of biodegradable natural building materials such as wood, cork, wool, and goat hair carpets, or were sourced from recycled waste, for instance plastic reclaimed from the ocean. As far as possible Oslotre used semi-finished products and standard formats with a minimum of penetrations, intended to support their universal application in the lifecycle to follow. In the central zones, downstand beams were interrupted to permit installing service lines without collisions and enable simple reversibility.
The basement consists of reinforced low-carbon concrete and serves as a plinth above grade, thereby compensating the elevation change of the site, sloping in two directions. The raised green antespace allows users and visitors to access the entrance hall. Six broad seating steps lead them downstairs to the hall and the cantina. This area is also used for events, and its full storey steel and glass facade presents an open character to the streetscape. The flexible 5 × 5 m column grid of the timber structure permits creating different office types, ranging from cellular to open plan office. A roof terrace complements the diverse set of spaces, extending them outdoors. The many custom solutions resulted in a simple building system that allowed occupying Haseltre following a construction period of only eight months.
