Raw Materials

  • Cardinal, Kuraray

Grotto Sauna

High-performing, insulated glass units, comprised of 2-3 plies of glass.
A low-e coating was applied to the interior glass lite and silicone was used as a secondary sealant for its superior mechanical and heat resistance capabilities.
The insulated glass units underwent a heat-treating process and were tempered.


For this Georgian Bay gem, the team was challenged with unique requirements such as the Grotto Sauna’s location (perched on granite bedrock, part of the southern edge of the Canadian Shield and ubiquitous to the 5,800 sq m bay), a “pedestrian skylight”, high temperatures and small window openings. Careful consideration and planning was necessary to achieve these high-performing, insulated glass units and ultimately create the most optimal spa retreat. The custom IG units are comprised of two or three plies of glass enclosing a hermetically sealed air space. Insulated glass was the most effective option to increase the window’s thermal performance by reducing heat loss.


The edges of the IG units have been placed far away from the opening in order to keep the primary sealant (butyl) away from high heat. A low-e coating was applied to the interior glass lite to stop the heat at its nearest point to the source and to reflect it back into the wooden oasis. Silicone was used as a secondary sealant for its superior mechanical and heat resistance capabilities, eliminating temperature as a concern altogether. The skylight was designed by AGNORA’s Senior Technical Specialist to withstand the snow loads and an occasional person standing on it. The glass has been laminated with SentryGlas®, an interlayer that has the highest resistance to high temperatures, while also retaining strength and clarity.


With such a small opening, a high light transmission was chosen to maximize the natural daylight entering the sauna. The low-e coating applied, while minimizing the amount of ultraviolet and infrared light that can pass through glass, doesn’t compromise the amount of visible light that is transmitted.


In order to provide greater resistance to thermal stresses, and achieve specific break patterns for safety glazing applications, the components were subjected to a heat-treating process and tempered. Tempered glass is a type of safety glass processed by controlled thermal treatments. It is four times stronger than annealed glass. Tempering shrinks the faces of the glass thus putting the outer surfaces into compression and the inner surfaces into tension.
This imprisoned energy causes the glass, when broken, to shatter into small, granular chunks instead of splintering into jagged shards. The granular chunks are less likely to cause injury.

Learn more about this incredible project from Partisans.