Volume 23, Issue 1 - January/February 2009

A Light from Within

Glass Helps Illuminate Oakland’s New Cathedral
By Ellen Rogers

Imagine the visual appearance of a building changing before your eyes, simply from the passing of light over its surface. The façade’s characteristics evolve as the sun moves from shining brightly upon it, to disappearing behind a dark sky. The use of light in architecture can render stunning results. And while the concept is not new, its use as a design focus in Oakland, Calif.’s Cathedral of Christ the Light (winner of an AIA 2009 National Honor Award) is unique. Designed by Craig Hartman of Skidmore, Owings & Merrill LLP’s (SOM) San Francisco office, advanced technologies were employed in order to create a “luminous structure and evocative architecture with modest materials while minimizing the building’s ecological footprint.” Simply put, without the use of glass as a major design element, the resulting project would not have been the same.

Groundwork 

Located on a two-block site that overlooks Lake Merritt, construction of the Cathedral of Christ the Light began in 2002 with initial design work and was completed last September. Before the actual design began, the Catholic Diocese of Oakland organized a detailed selection process to find the right architect for the job. 

“They went through a lengthy process of first reviewing individual design portfolios and then [those being considered] had to respond to written questions asked by the diocese about certain approaches to architecture,” says Hartman. “From there, it went on to interviews and the diocese continued to whittle down the group until there were three: Santiago Calatrava from Spain, Ricardo Legorreta from Mexico and us.” Hartman says SOM was actually not the firm initially selected. However, a few months later the diocese decided to go with SOM.

“They called me back and asked if I would still be interested in building what I had done for the design competition,” says Hartman. “I said yes, and they said OK, as long as you stay within the budget.”

From the beginning, Hartman says this cathedral was not to be like any other cathedral.

“The diocese wanted the cathedral to represent the aesthetics, technology and architectural design of our current place in time and not a historical replica,” says Hartman, who explains there were two key initial design considerations.

“First was the site and then second was a personal interpretation of what the history of the church has been in terms of space and especially light,” says Hartman. “In regards to the site, we are on the Pacific Rim and in a place that is extremely multi-cultural, so we were not designing for a single culture. And then also, was making a building reflective of the Catholic Church’s history in a way that was not just about replicating forms from the past, but trying to find the essence of what that sacred space might be.” 

Follow the Light 

To develop that essence, Hartman worked extensively with glass. He used it to create the qualities of a lantern that would glow during the day from sunlight and in the evening from the light within.

“In the context of the overall building, glass is the outer veil, providing protection for the sanctuary, which is made of wood,” says Hartman. “The glass creates an enclosure for the building that constantly changes with the light here in the Bay Area. Because of the way we treated the glass, with the fritting and the translucency, when you have direct light on the surface it becomes a solid object in its appearance and at other times, as the light moves around, it’s designed to allow light to strike the veil from the back side as well as the front surface so that it becomes very luminous.” 

Energy Performance 

In addition to aesthetics, the building minimized the use of finite resources, be it fossil fuels or the materials actually used in construction and operation. The cathedral was designed so that a minimal amount of energy is needed to heat and cool it. In fact, artificial lighting is only needed at night. The veil glass, which was supplied by Viracon, played a significant part in making this possible.

“For the veil wall, the glass assembly is an insulating, laminated fritted unit. And each assembly component has its own performance task,” explains Keith Boswell, technical director for SOM. “The insulating glass (IG) units were used for two reasons: first, to provide the highest-performing make-up of low-E IG for minimizing heat gain and heat loss. Secondly, since we are going to have a temperature gradient from low to high due to the displacement cooling, we needed to minimize the amount of condensation we would get compared to either a laminated unit or a monolithic unit.” (Editor’s note: through the displacement cooling system only the lower 15-feet of the building is cooled; the upper end is not heated at all. Radiant heat is used in the floor during winter months.)

Boswell adds that laminated glass was used primarily for acoustic reasons, mainly to mitigate outside noise from being transferred inside the sanctuary.

“And then the fritting that we used on the number-two surface does several things. One, it provides the amount of shading or surface for the light to shine on from either outside or in for the desired effect, either night time or day, and it allows the quality of the light coming through the glass to change as the sun moves across it.”

The First and the Last

Perhaps one of the most awe-inspiring features of the cathedral is the Omega Wall, which re-images a 12th-century sculptural depiction of Christ from the façade of Chartres Cathedral in France. 

“There are two ends of the building, the entry side (the Alpha wall) and the alter side (the Omega wall). The entry end faces due south where there is bright, direct sun,” says Hartman. “In both walls we have a surface of glass on the exterior, which is triangulated in order to allow the surface to conform to a compound, complex surface. There’s a curve at the base and it tips inward and upward and creases at the top. The sanctuary within is protected by a second layer of 1/8-inch thick aluminum panels that mirror the glass in a triangulated pattern. However, the aluminum (which is about 18 to 24 inches in board of the glass) is designed differently in the way it relates to the light. On the Alpha side we have tipped these triangulated panels inward as they move upward, and as they tip back and forth between one another. We can take the very direct, bright sun from the south, bounce it off these inwardly tipped panels onto a neighboring panel—much like the pedals of a flower opening up to bright sunlight—and that creates a dramatic condition of light on the panels.”

Hartman continues, “It’s the same design on the Omega wall except the aluminum panels are folded up tight against one another. What we have done there is perforate those panels with small holes that range from ¼ inch to 1-¼ inches and within that range there are about 140 sizes from big to small. We used these to create a gray scale and using computer techniques we applied this to a scan of a re-created image of Christ. We’ve translated that into this veil where you read pixels of light coming through these openings in the metal from the translucent glass behind.” Hartman says that while the image could certainly have been created via digital printing, it would have been rather predictable. 

“The idea was to make this image, like that of the overall building, change as the quality of light changes. So it comes and goes; it really is like a veil, which sometimes, depending on the nature of the light, is very strong and vivid. That’s typically when the light is strong on the outside and less so on the inside. As you get more light, either through light coming off the ceiling and down on the surface of the image or as light becomes brighter on the inside moving toward evening … that begins to diminish in its intensity,” Hartman says.

The glass used in the Alpha and Omega walls is a laminated assembly that has two clear lites with a PVB interlayer. According to Boswell, probably the most interesting technical aspect is its width. 

“Both the planned elevation and section geometry are very compound and ever-changing as it goes from the bottom to the top,” says Boswell. “So the reason that the lites of glass in their final form are triangulated is to accommodate the multiple geometries in plan and elevation to get them to resolve and close back on the veil walls.”

Installation Tactics

Webcor Builders, the general contractor, invited Enclos Corp. to install the glass. 

“Enclos worked closely with Webcor assisting the design team in the development of the unique concepts,” explains John Fulton, who works in design and pre-construction for Enclos. “We were responsible for engineering, designing, manufacturing and installing the majority of the cathedral and rectory building exteriors. Our scope included the cathedral veil unitized curtainwalls, oculus skylight, veil wall skylights, point-supported/suspended Alpha and Omega walls and interior sunshades (including the perforated art work), baptistery skylights, reliquary wall windows and skylights, doors, entrances and storefronts.” 

Group Effort

In order to ensure a successful project, communication and coordination were critical components. Boswell says for both the outside veil walls and the Alpha and Omega walls it was an iterative process with both Viracon and Enclos.

“We developed our base system and base materials, came up with a suite of design details—what we wanted to see in geometry, what we wanted to see in profile and what we knew we had to meet in performance—that we provided to the fabricators,” says Boswell. “We would then get commentary back on what was possible with not much effort, what was possible with a lot of effort and what we should possibly think about a little bit further. We did that to get enough input not only on design but on the build-ability of the system and the infill materials and then developed a few more details with the final details coming from actual shop drawings provided by the subcontractor.”

Bob Paal, a Viracon sales representative involved with the job, says, “The primary focus of the design team was proper balance of light and translucency of the glass. We also worked closely with Enclos once they were awarded the project. The entire project team traveled to Minnesota to view the mock-up glass prior to being crated for shipment to assure everything was correct.”

According to Fulton, the working relationships Enclos has with both SOM and Viracon have proven critical over many years, as the firms have worked together on numerous projects. “In a lot of ways, this was just ‘business as usual.’ On the cathedral project, Viracon provided all of the custom, trapezoid-shaped, silk-screened pattern glass for the veil curtainwalls and the triangular point-supported Alpha and Omega wall. No one glass lite is square, and no two lites are the same size,” says Futon. “There was a lot of careful study by the team members regarding glass sizes and patterns generated by computer modeling.”

Pushing Through

Aside from the build-ability of the project, there were also technical challenges. One in particular involved the Alpha and Omega walls.

“With that level of complex geometry, it has been one of our best examples of sharing information directly from design team to builder team; one in which we built the 3-D model in planned elevation with all of the points defined and then delivered that information directly to those who were fabricating and installing so that they could take direct 3-D information and develop their drawings from that instead of having to interpret a set of drawings.”

Fulton agrees.

“The cathedral’s complex 3-D geometry in combination with the unique wood structure had one-of-a-kind challenges for a curtainwall contractor. Elements of the building, such as the Alpha and Omega walls and their sunshades, could not have been created without the aid of 3-D computer modeling.”

Hartman adds that cost was always a significant issue. 

“We were constantly working to make sure elements served double uses and we were always editing the project down to what the essence of it really was,” he says.

Ray of Light 

Per direction from the diocese, the cathedral had to be built in such a way that it would still be standing centuries from now. It’s also a significant example of how glass can be used to create something that’s actually more than what it may appear to be. 

“In terms of using of glass, the idea was to create an architectural structure about light and the atmosphere so that you [see] the building [differently] throughout certain times of the day. What’s new and different is that you also read it with light from within; the light is carried from the sun striking the inner side of the veil in which the face itself [the image of Christ] becomes luminous,” says Hartman. “This building is trying to reveal light, both at nighttime from within and during the day from the sun, in the architecture and the fundamental quality of the building itself. With glass and with the treatments of glass all brought together, we were able to revel light in this way.”

Hartman adds, “What we have done is consider glass not just for its transparency, but about how glass can be used in combination with other materials to create a more profound experience of light.” AG

Ellen Rogers is the editor of the Architects’ Guide to Glass & Metal.

Architects' Guide to Glass & Metal
© 2009 Copyright Key Communications Inc. All rights reserved. 
No reproduction of any type without expressed written permission.