At the new campus of the Pudasjärvi School in northern Finland, the prevalence of timber creates a multisensory experience. Wood is seen, felt, and smelled in the school’s exposed log structure, branching glulam columns, and cladding. It even affects what occupants hear—or rather, what they don’t hear. Wood naturally absorbs sound, quieting the environment, says project architect Pekka Lukkaroinen, who recently retired as the founder of Lukkaroinen Architects in Finland.
In a country famed for its evergreen forests, centrally located Pudasjärvi (population 8,000) has been branded the country's “log capital” due to its enviable timber supply and the presence of Kontio, one of the world’s largest log manufacturers and a major employer in the area. When Pudasjärvi School was completed in late 2016, the 105,250-square-foot campus became what the firm believes is the largest log building in the world.
The school, located on the banks of the Ijoki River, consists of four volumes grouped into two wings connected by a dining area. The two-story volumes to the north host administrative offices, a gymnasium, art studios, a metal shop, and the kitchen, while the single-story volumes to the south host classrooms.
Structurally, the buildings are nearly all wood, with solid walls made of Kontio’s interlocking laminated pine logs. Nearly 11 inches thick, the logs provide all the insulation the building needs, Lukkaroinen says, and eliminate the need for interior finishes. For intermediate floors and stair banisters, the architects specified cross-laminated timber.
Topping the largely rectilinear buildings are hipped roofs punctuated by boxy skylights, called “lanterns” by the architects. In the single-story classroom buildings, the lanterns are 22 feet wide and 23 feet to 34.6 feet long in plan, and project more than 10 feet above the roofline. They are supported by curving, glulam pine columns, which splay out from a central node roughly 10 feet above the finished floor and connect to the lanterns’ roof beams, stiffening the timber frame. “The Y-shape of the columns is not only aesthetic, but also a functional choice in spaces where an excess of columns needs to be avoided …. [T]he weight of the roof needs to be distributed to multiple load bearing points in the roof structure,” Lukkaroinen says.
The columns measure 6.5 inches wide by 14 inches deep, and stand up to 36.6 feet tall, arching with a relatively shallow radius of 28.4 feet. In plan, the columns form an X at their base and are joined together with ½-inch-thick knife plates that likewise form an X, 3 feet in length. Each column utilizes two such plates along their height, secured by using three bolts and up to 18 screw, all 12 millimeters in diameter. “The bigger bolts provide easier initial assembly and take higher loads, and the screws surrounded by wood are better protected against heat in the case of fire,” Lukkaroinen says.
At the roof, the curved members connect to neighboring columns via embedded steel knife plates with angled 13-inch-long blades. Lukkaroinen Architects worked closely with the structural engineers at Stockholm-based Sweco to develop the connections (architects are not permitted to draw structural details in Finland).
The glulam was fabricated at Kontio’s facility just outside Pudasjärvi and trucked to the site. Inside the school, the wood was left exposed, finished only with a clear wax coating. In a novel arrangement, the company is responsible for maintaining the school’s timber structure for 25 years due to the large-scale use of Kontio’s log system.
All told, the school used nearly 92,000 board feet of pine logs, the majority of which were harvested in the immediate area. “We wanted to create a unique character for the campus that would present, at the same time, the long history of the woodworking in the area as well as a modern and forward-looking atmosphere,” Lukkaroinen says. “Wooden architecture has always had a special place in the Finnish architect’s heart, and we are delighted to see a revival of wooden architecture going on in Finland.”