By Dovetail Communications

First published in Wood Design & Building, 2020

Joensuu is a small but growing city – where more than 10% of the population attends either the University of Eastern Finland or the Karelia University of Applied Sciences – student housing solutions are a priority.

The Joensuu Lighthouse timber building in Joensuu, Finland. Photo by Commons Wikimedia

The Joensuu Lighthouse timber building in Joensuu, Finland. Photo by Commons Wikimedia

Completed last year, the 14-storey Lighthouse Joensuu is Finland’s tallest wooden high-rise building, containing 117 student apartments and rising close to 165 ft. The city’s zoning plan specified that the site should utilise high-rise construction, favouring wood. As a result, the architects devised an all-wood plan (beyond the concrete ground floor) with innovative design features, including an exterior stone tile facade featuring a lightwork installation by Finnish ‘light artist’ Kari Kola.

The project’s goal was to minimise costs by using an efficient floor plan, optimised structures, and innovative technology. To that end, the ground floor and civil defence shelter – a standard requirement for occupied buildings over 12 917-sq.ft. (1 200m²) in Finland – are made of concrete, but the remaining structure uses LVL floors and CLT walls, including for the elevator shaft. The structure is stiffened with numerous steel rods inside the wooden structures, tensioned from top to bottom.

The ground floor includes sauna facilities, a laundry room and adjacent drying room, technical facilities, and storage spaces for household and outdoor equipment. Floors one to 13 have nine apartments each, of which two are one-bedroom apartments and the remaining seven are studios, with the apartments varying in size from almost 280 sq. ft. to slightly more than 510 sq. ft.

Although the apartment building is made of wood, very few wooden surfaces are visible in the finished building; most interior surfaces are clad with gypsum board to meet fire safety requirements. The fire safety design for the building is based on functional fire design, as the standard E1 tables only cover wood buildings up to eight storeys high. Sprinklers were installed throughout (OH1 level, two-way water supply), but the building was designed to withstand a fire even if the sprinklers do not work. Building regulations require third-party inspectors for both fire safety and structural design; in addition, the ventilation systems were evaluated according to government standards.

Completed on schedule, each mass timber storey of Lighthouse Joensuu took less than two weeks to build. The panel blanks arrived at the construction site, where the window and door openings and the conduits for building services were then machined under the cover of a tent. The mass timber elements were then installed as the weather permitted. After installation, each completed storey was protected by a temporary roof to maintain the dry chain.

Lighthouse Joensuu’s wood components – almost 70 630 cu.ft. in total – store a quantity of carbon equivalent to the annual emissions of approximately 700 passenger cars. The Karelia University of Applied Sciences conducted measurements, acoustics research and evaluated the structure’s carbon footprint; studies to-date reveal that only about one-fifth of the carbon footprint of Lighthouse Joensuu was generated during the construction period, and the remainder is operational, which is still under analysis.

The project – which won the 2019 Puupalkinto Wood Award and is nominated for this year’s International Award for Wood Architecture – was also supported by Finland’s Ministry of the Environment. As one of the tallest structures in the town, Lighthouse Joensuu illuminates the skyline at night and acts as a beacon – both for the town and for the future of wood construction.

Client: Opiskelija-asunnot Oy Joensuun Elli Joensuu, Finland

Architect: Arcadia Oy Arkkitehtitoimisto Joensuu, Finland

Wood engineering: Joensuu Juva Oy Joensuu, Finland A-Insinöörit Tampere, Finland

Wood supplier: Stora Enso Varkaus, Finland

General contractor: Rakennustoimisto Eero Reijonen Liperi, Finland