A colonnade of whole charred tree trunks supports the roof of Puusauna, a sauna and tea room in Finland designed by architect Jaakko Torvinen.

Located on the small island of Kaunissaari in the Gulf of Finland, the 30-square-metre sauna sits at the boundary where a large forest meets the beach.

Charred tree trunks support this Finnish sauna

Puusauna, which means Tree Sauna in English, was constructed almost entirely using trees from this neighbouring forest, which have been hand-hewn and left as whole trunks to create sculptural structural elements.

Sheltering an external terrace is a canopy supported by charred tree trunks, building on a technique used by Torvinen for his previous project, Little Finlandia – a temporary events space in Helsinki supported by load-bearing pine trunk columns.

Jaakko Torvinen designed it for a site in the Gulf of Finland

"This is something I think is at the core of my design – using the organic shape of wood as part of the architecture," Torvinen told Dezeen.

"The trees were selected one by one from the forest according to their individual, natural forms. These trees play a central role and appear as prominent elements in the building."

A whole tree is incorporated into the bannister

Puusauna was designed as a traditional loft sauna, with washing spaces located on the ground floor and the sauna itself upstairs.

Wrapped by dovetailed log-cabin walls made from hand-hewn trunks, the sauna is organised around a batch-fired stove, which was specifically chosen for its "slow, hands-on" heating process.

A colonnade of charred tree trunks supports the roof

A timber staircase with a whole tree trunk acting as the bannister's newel post leads up to the sauna benches, which face a large, panoramic window overlooking the ocean. A second window behind frames the forest.

"As a Finn, I sauna almost every other day and swim outdoors at least weekly – also in winter – so this deep, personal relationship with sauna culture is directly reflected in the design," said Torvinen.

"After a sequence of compressed and sheltered transitions, the visitor steps into a tall, over four-metre-high volume where an organically shaped tree trunk rises through the space and draws the gaze upward," Torvinen added.

"The architecture is intentionally restrained in how it reveals views: they only open once you sit down – first while washing, and later on the upper benches – turning the act of bathing into a slow, choreographed ritual rather than an immediate visual experience," he added.

A window in the sauna frames the forest

Alongside the sauna, the 10-square metre tea room is organised around a small wood-burning stove. Its design was informed by traditional Japanese architecture and features end-grain wooden flooring and a bench that ends in another small twisting tree trunk.

Both the sauna and teahouse are wrapped by a deep timber terrace, framed by a colonnade of charred tree trunks and featuring a large boulder that Torvinen had been particularly drawn to when first visiting the site.

Other sauna projects recently featured on Dezeen include Watercave, a timber sauna that floats atop a Norwegian lake, and the Drying Shed, which Built Works created in woodland in East Sussex.

The photography is by Päivi Tuovinen.