• Stack principle

    Stack principle

  • Axonometric of seperat studs

    Axonometric of seperat studs

  • Axonometric of combined studs

    Axonometric of combined studs

  • Plan


  • Drawings and model

    Drawings and model

  • Model and built structure

    Model and built structure

  • Usability test in model

    Usability test in model

Thermal Mass Sauna Stack


Anders Berensson Architects has designed a Sauna as a cave like stack of wood studs where the thermal mass of the timber absorbs heat and releases it when bathing. The design was commissioned and made in dialogue with legendary photographer and sauna connoisseur Mikkel Aaland in Ulefoss Norway. Mikkel asked for a design of an organic shaped wooden sauna with the finish Sauvasauna as role model. To do so we had to reinvent both the structure and the building physics of the modern Nordic sauna.

The design takes it starting point in the commission to design a womb like organic shaped wood space to be used as a sauna. When designing the sauna, we decided to aim for an organic wood structure without the use of glue like in plywood and glulam. To do so we designed a cube of stacked 2 by 3-inch fir tree studs that we subtracted into a cave like shape. In most parts the cave is stacked with straight cut studs but where the body meets wood the studs are jigged sawed and sanded into a smooth surface.

When talking to Mikkel during sauna sessions as well as reading “Sweat” Mikkels epos on saunas we got inspired by the Savusauna. A structure based on that the whole room is heated in advance so one can enjoy the heat from the warm stones and wood in fresh oxygen rich air when the heat source is put out. This led us to look back at the history of the Nordic sauna searching for the essence of its construction principles

Photograph of  a savusauna by Mikkel Aaland, www.mikkelaaland.com

During the last century when going from a standalone structure to be incorporated into a modern house the Nordic sauna made the same journey as most other wood buildings, becoming less and less wood and more and more insulation, moist and wind barriers and composite materials. The sauna typology however hardly benefits from this development. It don’t need thick insulation since it’s heated for short periods of time and the experienced heat is manly a direct heat from the stove or the charged thermal mass of the space. A sauna hardly needs plastic sheets and other chemical products that emits chemicals when heated. A sauna when used as a one time a day standalone heated space for sweating is better of in its original design with little insulation and a big thermal mas.

While rediscovering the traditional building physics of the Nordic sauna we wanted to improve and modernist our project to be a typology of its own. With this in mind we tried to optimize the thermal mass of our wood stack looking at our structure as a heat battery. Therefore we developed a system of stacked studs with a 4 inch space between each stud creating big exposed wood surface to be charged with heat in advance and released when bathing the sauna.

Construction drawings

How to build

A 2 by 3 foot fir tree stud (45 X 75mm stud) is a Nordic of the shelf product normally used in non load bearing walls. This is our only building part for the sitting structure. The stud is stacked with a distance 4 feat (95 mm). When creating a seating area the gap is filled with a stud making the gaps between the studs 10 mm. The studs are screwed together and the wholes are plugged when visible. Since the structure is made in a 3D program all studs can measured and cut in advance. Since the structure is in wood alterations such as smoothing surfaces can be made after the structure has been erected. A physical 1:10 model is sent to site as a construction drawing to simplify the understanding the final outcome.

Stop motion movie in 1:10 model

How to use

The lowest level is reached directly where you enter the sauna. The second level is an introvert space where you can crepe in to the wood structure. The third level you sit next to the old window looking out towards the fjord.