On an island within the Finnish archipelago, a sleek, pebble-shaped sauna seems to delicately balance atop a small rock formation. Called Kivi Sauna, the structure was designed by Helsinki-based design and architecture studio Sotamaa.

The firm’s design process was guided by a desire to foster a deep connection between the sauna and its surrounding environment, which is defined by the sea and the island’s stark rock landscapes.

The sauna was constructed with mass timber, specifically Cross Laminated Timber (CLT) sourced from Finnish forests. Its interior features vast CLT sheets, while its exterior is crafted from milled CLT panels. Between these layers lies a sturdy timber frame. The structure’s exterior is clad in Leadax, a waterproof membrane derived from recycled car windows, which functions as a sustainable replacement for traditional lead roofing. The material’s gray hue echoes the colors and reflections of the surrounding rocks and water.

The sauna’s entryway includes a small terrace and a stove hatch, which was designed to receive firewood from outside. This ensures the interior remains warm and clean. 

Inside, a large black volume houses the stoves for heat and hot water. The top level features an expansive horizontal window that offers panoramic views of the archipelago and the sea.

Kivi Sauna was designed to withstand extreme weather conditions. Its aerodynamic form allows it to fend off gale-force winds, while solid rock foundations and the cantilevered structure protect the sauna from flooding, stormwater, ice, and snow. In addition, the double-skin solid timber structure allows for proper ventilation, and the inner skin’s design eliminates unnecessary voids under the seats, which improves heating efficiency and prolongs warmth retention.