Originally conceived by CLT Plant Oy from the town of Kauhajoki in Western Finland, the terraced complex of four small saunas, called Villa Lilla, was completed on a quick schedule. Work on the site began in March and reached the finishing stages around Midsummer. One of the factors speeding up the construction was the use of lightweight, easy-to-process cross-laminated timber, or CLT.
The construction materials used for the terraced saunas are 100% Finnish.
“We ordered the sawn timber used as raw material for CLT from Metsä Fibre, because we value its Finnish origin and consistent quality very highly,” says Miikka Vainio, Managing Director of CLT Plant.
The grooved CLT wood materials and lamella are made of sound-knotted Finnish spruce that Metsä Fibre supplied from its Vilppula sawmill. Even the glue used in the production of CLT elements is Finnish. Made by Kiilto Oy, the glue is an M1 classified PUR product that resists vaporisation and retains its adhesion in extremely hot conditions.
“When it comes to strength, Finnish softwood is the world’s best. Finland also offers advanced sawmill technology, which provides an excellent basis for the production of CLT,” says Vainio.
Finnish origin is an absolute requirement for us in CLT products.
Special drying guarantees quality
The sawn timber used in CLT construction must be specially dried, which according to Vainio, is another of Metsä Fibre’s advantages as a raw material supplier.
“During the special drying process, the moisture content of sawn timber is reduced through a precise chamber drying process to 12 per cent, compared to the 18 per cent typical of ordinary shipping-dry sawn timber. Special drying is a requirement for CLT gluing and sawn timber use indoors. It calls for a great deal of competence, technology and experience,” says Ville Valio, Area Sales Director, Europe, for Metsä Fibre.
As the saunas constructed on the Naantali Housing Fair site will be used all year round, the specially dried CLT material will really get to prove its strength as a construction material.
“The wood must endure temperatures of up to 100 °C when the sauna is in use, as well as temperature fluctuations caused by the changing seasons, which can be 50 degrees or more. This has been a very enjoyable project, which has allowed us to present the advantages of wood construction to a large audience,” says Vainio.
Wood construction that blends into nature
All in all, around 130 cubic metres of spruce was used for the indoor and outdoor cladding, steps and railings of the sauna buildings perched on the shores of the housing fair site. Metsä Fibre supplied 100 cubic metres of this.
Some of the wood was left unpainted, while other parts were treated with paints that blend into the surroundings. The black, teal and grey paints let the natural appearance of wood shine through.
“Why hide a great material like this? Let the life cycle of wood be visible,” says Vainio.
After the housing fair, the saunas will serve residents and travellers to Naantali, satisfying their sauna bathing needs.
Miikka Vainio 
Ville Valio