Kuvatoimisto Kuvio Oy

Ville Hara calls the timber skin of Helsinki’s Löyly sauna “the cloak.” The angular, geometric façade, interrupted by narrow slit entrances, conceals a second structure: a simple rectangular volume of black concrete that houses Löyly’s restaurant and public saunas, providing visitors a sense of privacy without limiting their views of the Baltic Sea. “From inside you see outside, but from outside you don’t see inside. It acts like a venetian blind,” Hara says, who founded Helsinki-based Avanto Architects with Anu Puustinen in 2004.

Opened in May 2016, Löyly—the Finnish word for the steam created by throwing water on heated stones—sits on the edge of a manmade peninsula just a mile from the center of Helsinki, as part of a planned residential development in what was once an industrial area. To preserve as much of the existing shoreline as possible—which was slated to be turned into a park—and avoid blocking the views of the soon-to-be-condo owners, Avanto designed a low, narrow building whose free-form “cloak” is meant to evoke a natural landform, an effect that will intensify as the heat-treated pine weathers to a stony gray.

Kuvatoimisto Kuvio Oy
Marc Goodwin/archmospheres

The project—spearheaded by actor Jasper Pääkkönen and entrepreneur and member of Parliament Antero Vartia—had several starts and stops following its initial 2011 proposal, but from the beginning, Hara says it was important to strike a balance between privacy and transparency. Formed by a series of sloping triangular planes created by thousands of wood lamellas, the cloak creates transitional spaces—open yet sheltered from the elements—for the periods before and after trips in to the sauna, and also shades the glazed inner volume. To the south, the façade flattens out to become stairs, which lead to a pair of roof terraces.

Hara says the overall shape of the cloak was designed in AutoCAD, but working out the dimensions and spacing of the lamellas took time. Half of the 4,000 lamellas are unique, he says, and each had to be modeled in three dimensions. The architects also worked with the carpenters at local Puupalvelu Jari Rajala Oy to build a full-scale mock-up of the façade. They initially used thinner wood members since structural requirements were minimal, but the skin was too transparent. Eventually they landed on 73mm (2.9 inches) as the ideal depth, spaced 130mm (5.1 inches) apart—the maximum height permitted for steps in Finland. (The dimensions of the lamellas do not change, even at the stair.) Avanto also used the model to test the lighting, and painted a portion gray to show the client how it would look after a year of aging.

Thanks to plentiful forests, timber is a popular building material in Finland. However, for Löyly’s cloak, Avanto selected a new product that the firm had never used: glued-laminated wood from a Finnish startup called Nextimber. The company, founded in Kuopio, Finland, in 2014, makes glulam out of forest thinnings (small-diameter trees removed from timber forests) and core residues from plywood manufacturing. Löyly’s heat-treated pine panels were baked and pressed to improve structural performance and weather resistance. According to Nextimber, this thermo-mechanically modified wood is 20 to 25 percent stronger than typical glulam. But it was attractive to Avanto because it is inherently sustainable, making use of a material—what Hara calls “trash wood”—that otherwise would go to waste.

The cloak’s structure is a complex skeleton made of hollow steel tubes. Originally designed to be freestanding, the timber skin was eventually tied into the interior volume in a dozen places. Round steel nodes were designed to accommodate the structure’s complex geometries, which created points where as many as six steel columns meet. Welded to each support are standard steel plates that support the wood lamella. With tens of thousands of connections, the joinery had to be “extremely simple,” Hara says, “because otherwise it starts to be very, very expensive.”

The pine planks were milled on CNC machines in Kuopio. Their outer edges were cut diagonally to continue the angle of the façade; a chamfer at the tip prevents breakage. Planks were then numbered and shipped to the site, where they were bolted to the steel structure. A slight angle allows the timber to shed water, keeping interior spaces dry and ensuring that rainwater doesn’t pool on the unfinished wood. Typically, Hara says, the glulam would be oiled, but the huge number of lamellas used on the project made this cost-prohibitive. If a single person were to oil all four sides of each lamella, it would take more than a year, Hara says, and by the time that person finished, they immediately “would need to start from the beginning.”

Thanks to its use of timber byproducts, last summer Löyly became the first FSC-certified structure in Finland. But Hara is just as pleased that the sauna is being used. Public saunas have become rarities in the past few decades, and Löyly is now a popular destination, even attracting the attention of The New York Times. Its success, he says, is good for the architecture profession in Finland, which has a reputation for being overly academic. “I see [Löyly] as a kind of propaganda tool,” Hara says. “With this kind of project, we can show that architecture is a positive thing, and it brings joy to the people. Without this architecture, it would be just a box, or a standard building, and it would not be the same."

Kuvatoimisto Kuvio Oy
Interior design, Interior Photography
Mikko Ryhänen / Joanna Laajisto Interior design, Interior Photography