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Grotto Sauna – A Canadian Prefab Sauna

The Grotto Sauna is a sculpted space designed by local studio PARTISANS, a sensual experience, and a sophisticated exercise in building science. Historically, grottos are secret, natural spaces within simple-looking rock formations. Their interiors are carved by natural forces to create sublime worlds of complexity and wonder, and as such this project is born from the rock and heat that shapes it inside and out.

Grotto-Sauna-By-PARTISANS-02-Jonathan-Friedman-759x497 Grotto Sauna / PARTISANS

© Jonathan Friedman

Nestled into the granite shore of a remote island near San Souci, Ontario, the Grotto is a sauna like no other. The Ontario Wood Award winning design by Partisan Projects of Toronto pushes the limits of what can be done with wood. The locally sourced Eastern White cedar interior is unfinished and mirrors the rock and water that surrounds it.

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© Jonathan Friedman

“The project is ambitious, yet very much in harmony with its surroundings. A great deal of time was spent understanding the site and determining the best way to integrate the structure into it – for instance, we digitally scanned the site to produce a highly accurate 3D model to design from so that we could fine-tune the building and have it emerge from the site in precisely the right way,” said Partisan Projects’ Alexander Josephson.

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© Jonathan Friedman

  • The Partisan team spent many months understanding the site, from the digital mapping to “examining the changing colours of the water, sky and granite, as the light changed from sunrise to sunset.” What emerged was the angular, rugged building that is a part of, yet distinct from, the surrounding landscape.
  • The project not only pushed the limits of the material but also the tools. Designers went so far as rewriting the software code of CNC machines to achieve their vision. Partisan worked closely with fabricators to “develop the process for achieving a stable panel with such complex geometry, while having all the grain oriented to align once carved.”
Grotto-Sauna-By-PARTISANS-15-Jonathan-Friedman-759x507 Grotto Sauna / PARTISANS

© Jonathan Friedman

Designers had to work closely with local authorities to resolve regulatory issues. The scale of the sauna was effectively reduced by half by moving the “building into the cliff and rotating its geometry to work with the landscape.”

“Given that the island is water access only, the most efficient way to complete the project on time and within budget was to prefabricate it in Toronto and deliver it to the site,” Josephson said. “Partisan managed the entire construction process, which involved coordinating the on-site construction team in Parry Sound with the prefabrication team in Toronto. Delivery to the site required a police-escorted convoy from Toronto, a 60-000 ton crane, and 2 barges to deliver the prefab building to the site.”

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© Jonathan Friedman

  • Josephson says that the limits of the skilled craftsmen involved were also tested in the hand-assembling of the interior. “Thus the project is a synthesis of cutting edge software, CNC technology and old-world craftsmanship.”
  • “We can really push the limits with wood, you can sculpt it, form it, bend it, seal it, and burn it,” Josephson said. “Moreover, it is inherently beautiful in its myriad natural forms and thoroughly engages all the senses which adds depth and subtlety to the work that other materials don’t achieve.”
Grotto-Sauna-By-PARTISANS-18-Jonathan-Friedman-775x1200 Grotto Sauna / PARTISANS

© Jonathan Friedman

Ontario Wood WORKS! Award Comment:

Wood was chosen for this private sauna, located on a remote island near San Souci, because it was the only material that could achieve the high list of demands for the project. For the interior, wood is essential to the performance of the sauna. It is able to absorb heat and humidity, yet retain its stability and remain comfortable to the touch. Wood also enabled the freedom to carve the sensuous forms of the interior. It is smooth and pleasurable to touch. In addition, all senses are engaged inside the sauna – the wood creaks as it is heated and the smell of cedar is unmistakable. Locally sourced Eastern White Cedar cedar was used. The wood is also very much alive – it expands and contracts, and will change in colour and texture over time as its users engage with it. At the exterior, the burnt wood cladding continues the interior narrative of steam, water and heat. It provides the superior flexibility, longevity and beauty that needed for this demanding and complex project.

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© Jonathan Friedman

Due to the remote and difficult nature of the site, the only way to achieve the precision and sophistication of the interior was to prefabricate the building and deliver it to the site via a barge and crane. Prefabrication off‐site meant that the builder spent only three weeks on site (doing foundations, finishing the cladding and connecting services). Given that bringing materials to the island is a six hour round-‐‐trip by barge, minimizing the time spent on site saved tremendous labour and energy, and minimized site disturbance resulting from the construction process. Thus the project is an example of a highly sustainable method of building in Canada’s remote areas.

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© Jonathan Friedman


Perched at the north-west edge of a private island, the Grotto Sauna is a sculpted space, a sensual experience, and a sophisticated exercise in building science. When PARTISANS met on site, they knew that their most prominent challenge was to make a free-standing structure that not only respected, but also matured from the context. Contemplated research was conducted, and through the process a Grotto was set as an inspiration that would inform the design. Grottos, historically, have been known as natural or artificial caves that are embedded deep behind the curvature of streams, and thus discovered by those who would take the time to explore.

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© Jonathan Friedman

The site is a prehistoric large-scale rock formation, and understanding it intimately was the first step toward architecture. The selected concept prescribed a solid, simple presence on the exterior, while the interior followed dynamic air movements in curvature forms; requiring design solutions. Challenging the standards of current practices in the construction industry, we worked directly with a millwork and steel fabrication partner on every detail. Together, we developed a new process of fabrication; utilizing state of the art 3-D technology to scan, model and build the Grotto.

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construction process 05 – © PARTISANS

Project Data:

Project name: Grotto Sauna
Location: Bernyk Island, The Archipelago, Ontario, Canada
Coordinates: 45.216138, -80.143835
Type: SPA Interior
Project Area: 800 sq.ft (72 sqm)
Status: Built
Completion Year: 2014


  • 2015 – Interior Design Magazine Award – Best in 10 Award – Category: Beauty/Spa – Winner
  • 2014 – Ontario Wood WORKS! Award – Winner
  • 2014 – Interior Design Magazine Award – Category: BEAUTY/spa/fitness – Best of Year – Project Winner

The people:

Client / Owner / Developer: Private
Architects: PARTISANS – 1139 College St, Toronto M6H 1B5, Canada
Design Team: Alexander Josephson, Pooya Baktash, Jonathan Friedman, Shamir Panchal, Ivan Vasyliv, Betty Vuong, Nathan Bishop
Contractor: Jordan Construction, Chantler Barging
Lighting Consulting: G2J Design Inc
Project Management: Partisans
Engineer: Moses Structural Engineers Inc.
Text Description: © Courtesy of PARTISANS, Ontario Wood WORKS! Award
Images: © PARTISANS, Jonathan Friedman


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