Undulating Curved Glass Curtainwall Highlights 7th St. Thomas in Toronto

Located at the intersection of St.Thomas and Sultan Streets in Toronto, 7th St. Thomas represents a new concept in commercial real estate.

Designed by award winning architect Harry Pontarini, 7th St. Thomas is a nine-story building with 93,000 square feet of luxury office condominiums for businesses or individuals who want to own their own office space in an upscale Toronto neighborhood.

The unique and eye-catching design features a new modern glass tower built on top of six historical Victorian townhome facades that were original structures on the building site.

The historical building structures were maintained and preserved in sharp contrast to the undulating glass curtainwall rising nine stories above the original brick and stone.

BV Glazing Systems (formerly Global Architectural Metals), was contracted to furnish the curtainwall system for the glass tower. A unitized system was designed to facilitate installation in a relatively congested urban jobsite. 

The 4-sided SSG curtainwall system included curved insulated glass installed in convex and concave elevations to create an undulating wall.

The bent insulated unit specification included tempered and/or heat strengthened glass with a High Performance Low E coating, combined with white decorative frit lines that created a gradient fade on the glass surface.

Standard Bent Glass Corp of Butler, PA was selected as the curved glass supplier for the project. With 80 years of experience in custom glass bending and an industry leader in decorative glass fabrication, SBG was uniquely qualified for the project and the challenge.

The challenge was to incorporate High Performance Low E coatings and ceramic frit patterns on curved surfaces that are installed in both convex and concave elevations, within the limitations of bending and tempering glass.

1. High Performance coatings can only be fabricated on the concave surface of bent glass. (See Detail # 1).
2. Ceramic frit patterns can only be coated on the concave surface of bent glass.
3. The building elevation features units viewed from both convex and concave (See photo)
4. To best feature the white decorative frit, in all cases the frit should be to a more exterior surface (in front of) the Low E coating.

The process to satisfy all the unique elements of the job included close communication and “brainstorming” sessions between the curtainwall contractor and glass bender to develop the make-up of the curved glass.

The High Performance Low E selected for the project was Guardians 6mm SN68 coating on a low iron glass substrate.   Guardian SunGuard products can be post tempered and are bendable.

Standard Bent Glass is a certified Guardian SunGuard Select™ Fabricator. Low Iron glass was chosen to eliminate the tint in clear glass from compromising the color of the white gradient frit lines. 

Super Neutral (SN) 68 was selected as the Low E coating because it can be applied to the #1 and/or #3 surface of an insulated unit for aesthetics and performance. This choice was critical for the convex and concave installation of the curved glass.

For aesthetic reasons, it was important to feature the white gradient ceramic frit lines as close to the 1st surface (exterior) of the glass unit as possible. 

In addition, the SN 68 coating needed to be in back (towards the interior) of the white frit.  This would prevent the metallic coating from obscuring the white frit in any way. 

To meet these requirements, all the curved insulated units (convex and concave) had a laminated exterior lite and a monolithic interior lite. 

The combination laminated insulated unit included 3 lites of bent glass with six (6) corresponding glass surfaces.  

As previously mentioned, Low E coatings and ceramic frit can only be fabricated on the concave surfaces of bent glass.

The resulting bent glass unit make-ups are as follows:

Convex View:  White Gradient Frit   #2 Surface (Concave)

SN 68 Coating-  #4 Surface (Concave)

Concave View: White Gradient Frit   #3 Surface (Concave)

SN 68 Coating   #5 Surface (Concave)

In all conditions the White Gradient Frit is to the exterior of the Low E Coating. Visually the glass is consistent and identical, as the curtainwall undulates from convex to concave curves.

Standard Bent Glass created the Gradient Frit with Dip Tech direct-to-glass digital printing technology.  

This process provides excellent repeatability and registration so that the graphic patterns for adjoining glass units match vertically and horizontally with strict tolerance. The process can be incorporated with laminated or monolithic glass.

Curved or bent glass units are typically insulated with flexible spacers to accommodate the shape of the glass. 

The curved glass on this project is installed in a silicone structural glazed curtainwall system with bent glass units in excess of 50 square feet. 

To meet those demands, Standard Bent worked with Quanex Building Products to incorporate the Tri Seal™ Flex spacer. 

Tri Seal™ Flex is a warm-edge flexible silicone spacer specifically designed for the challenges of bent glass and the requirements of SSG systems. 

The spacer profile includes a flexing channel to accommodate slight variations in radii between the bent glass lites of an insulated unit. A secondary silicone is applied for structural integrity.  In addition, the insulated units were argon filled to increase thermal performance.

7th St. Thomas is an excellent example of the recent growth in technology and manufacturing processes for curved glass in architectural design and construction. In years past, the design elements of 7th St. Thomas would have prevented the use of bent glass.

The curved elevations would have been segmented with flat glass because the combination of curved glass with High Performance Low E, custom decorative frit, and tempered lites could not have been accomplished. 

Today the dramatic undulating glass tower at 7th St. Thomas is a testament to the advancements in glass technology and the knowledge that bent glass can now match flat glass in performance and aesthetics for design of building facades.