A wooden shelter at Nemus Futurum

Latin for ‘Forest of the Future’, Nemus Futurum is Metsä Group’s visitor centre in Southern Finland. The three-hour guided tour through forests showcases sustainable Finnish forest management and visitors use tablets, GPS tracking and augmented reality for an experience of how different forestry activities affect the climate and forest biodiversity.

During the tour, visitors make an intermediate stop at Laavu, a shelter built from Metsä Wood’s products, mainly from Kerto® LVL (laminated veneer lumber). The shelter houses around 20 people at a time in a space of 17 square metres. A dry toilet named Huussi, also made of Kerto LVL and plywood, complements the rocky hilltop location. The use of Kerto LVL enables fast, light and green construction.

Sustainable Kerto LVL shows its strength as a construction material

The designer’s idea to shape the building following the growth rings of a tree while ensuring that it blends in with its surrounding nature posed a challenge for the load-bearing structure. The diminishing rings required six arc-shaped supports, each of them a different size. The ideal arc distance was determined in close cooperation between the architect and the structural engineer.

“The brief was to use Metsä Wood’s materials, such as the ecological Kerto LVL, but otherwise I had total design freedom”, says Teija Piirto, the designer responsible for the architectural solution. “I wanted to create something that blends into the surrounding nature while creating a feeling of being protected and sheltered, like a nest. Ideally, the building should also highlight the latest construction techniques.”

The load-bearing structure was made with Kerto LVL Q-panels glued together to form 75 × 250 mm arcs. The six arcs were designed so that they could be cut to shape out of larger panels in a CNC machining process with a minimum amount of material waste.

Lateral stability with sawn timber

Thanks to Kerto LVL’s strength properties, combined with the arc shape of the load-bearing structure, vertical strength was not a problem. Lateral strength, however, was more complicated. Because of Laavu’s location on a hilltop and its height of up to 4 metres with a vertical, large façade, the structure would be exposed to strong lateral wind forces.

To ensure lateral stability, diagonal support structures of 21 × 100 mm sawn timber boards were installed on either side of the building. These were complemented by additional sawn timber ribs placed diagonally and longitudinally. The cladding made of wood shingles was attached onto these ribs. The shingles were hand-made from spruce by a local carpenter.

“Lateral bracing was an interesting challenge because of the changing radius of the tapering arcs”, says Ville Pulkkinen, the structural engineer. “That’s why we decided to use 21 mm board as it could be sufficiently bent to follow the arcs. The architect made a 3D model of the structure that indicated how high on the arcs the diagonal ribs could stretch, and the rest was supported by longitudinal ribs.”

It was necessary to calculate the strength properties separately for both sides of the building because of its curved shape, with one side longer than the other.

Modern meets traditional

The vertically load-bearing arcs were fixed to concrete pillars anchored to the natural rock. The stabilising ribs were screwed to both inside and outside of the arcs.

Finally, the wood shingles used I the cladding, were attached to the ribs with nails following a traditional Karelian method using only one nail per tile to prevent warping and splitting. The shingles were also used on the inside to hide the ribs fixed to the insides of the load-bearing arcs from sight while leaving the arcs visible.

Material versatility combined with collaboration flexibility

Both Teija Piirto and Ville Pulkkinen say that as challenging as the design of Laavu was, it highlighted the versatility of Kerto LVL as a construction material. “This was my first project where laminated veneer lumber was machined into an unusual shape”, says Ville Pulkkinen. “Kerto LVL is an ecological and natural material for construction, and in fact, probably the only material that could be persuaded into the unique shape of the building.”