Congregation sings praises of windows

Few project teams receive an invitation to a church service to celebrate the completion of a window system renovation. Leaders of the First Unitarian Society of Minneapolis honored specialty glazing contractor Harmon Inc.’s Minneapolis team in front of their congregation, singing the fitting tune “I Can See Clearly Now” by Roberta Flack.

The Harmon team removed the original curtain wall of the church and replaced it with a high-performance, low-emissivity insulating glass and aluminum, thermally broken curtain wall. Consequently, the energy efficiency in the assembly spaces improved by 50 percent, and new aluminum and steel frames enhanced the aesthetics while preserving the original architectural design.

The original glass exterior of FUS represented one of the earliest examples of curtain-wall design in the Twin Cities.

“Designed in 1949 by Long and Thorsov Architects, the concept for this high span, glass to the front, wall system must have been revolutionary in its time,” says Steve Norton, director of sales for Harmon. “Thermally improved, pressure equalized curtain walls did not debut until the early 1960s.”

The use of warm brick massing elements, offset circulation patterns and large aluminum window-wall technology creates an optimistic and rational spatial experience that dramatizes the mission of the Society, says George Hutchinson, chair of FUS’ Building and Grounds Committee.

“As with other avant-garde architectural designs, the design vision exceeded the limits of the technology of the day,” Hutchinson says.

The historic curtain wall featured a steel frame supporting aluminum tubes laid out in a grid. Direct connection of the glass thermopanes to the aluminum tubes with exposed steel fasteners and exterior aluminum battens provided no accommodation to weep infiltrated water out of the frames.

“As the glazing compounds gradually failed, the glazing units sat in trapped water and the edge seals deteriorated,” Norton says. Additionally, he notes, “The internal metal spacers were made from a steel channel, rather than aluminum in common use today. Water trapped in the area between the exterior pressure bar and the aluminum tube provided ideal conditions for corrosion between the steel and aluminum components. Combined with incompatible steel fasteners, the proximity of dissimilar metals in a wet environment led to internal rusting and staining of the wall system’s interior surfaces, as well as a general breakdown of the wall’s internal structure.”

Glass failure occurred early in the curtain wall’s life cycle. “Glazing units began failing six years after the building’s original construction,” Hutchinson says. While the glazing was replaced, the root cause of the system’s deterioration was never understood or addressed, and the glass units continued to fail over a period of years. The Society continued to replace individual units on a regular basis until finally deciding to fix the existing wall system. FUS issued a request for proposals and selected Harmon to tackle the project.

Harmon’s four-step approach to renovation revealed the primary cause of the wall systems’ problems, defined a series of alternative designs and budgets and performed the work on a tight schedule.

1. Survey of field conditions

FUS and Harmon officials met to define the existing wall’s problems and discuss potential solutions. One approach suggested leaving the existing structural framework and applying a new glazing system on the exterior. A second idea proposed removing and replacing the entire system. Officials evaluated each approach based on cost, aesthetics and feasibility, potential disruption to the congregation, wedding planners and the nursery school inside the church.

The team also worked with the city inspections department to design and approve exit doors required at the lower-level assembly room. These doors were integrated into the architectural design of the window mullions, providing access to the exterior patio and code-required egress capacity.

2. Non-destruction field evaluations

The team conducted multiple evaluations to determine details of remediation options. Engineering and abatement experts were brought in by Harmon officials to help identify structural and potential asbestos issues. The consultants helped them define the best approach for handling asbestos containing materials present in the spandrel panels and glazing materials. The team prepared and issued reports detailing the two design options and budgets. “It became clear that the most effective solution was the complete wall replacement,” Hutchinson says.

3. Prove the solution

Harmon officials put up a field mock-up of the proposed solution. During removal of the glass, the consultants monitored and measured asbestos levels to confirm the best methods to abate these areas. Inspection of the interior of the frames validated the need for a complete replacement of the existing wall system.

4. Work the plan

Harmon designers produced the final shop drawings, and the Building and Grounds Committee reviewed and approved them. FUS staff and nursery school tenants reviewed the work schedules and activity plans for minimizing occupant disruption. Harmon’s team figured a way to gain access to the difficult site, and project manager Jeff Hackenmueller choreographed material deliveries. The workers built a temporary wall inside the lower assembly hall to limit disruption to the nursery school classes and eating areas. They placed a swing stage scaffolding on the roof of the auditorium to provide a platform for the crews, and a full-height interior scaffold in the main auditorium. The foliage on the patio needed to remain undisturbed for the upcoming wedding season. So, the workers delivered the glazing units, structural steel and the large aluminum ladder-frames with a crane, from the front entrance street, over the roof of the building and into the courtyard located a story below street level.

The Harmon team worked for seven weeks, between July and August 2003, and completed the project about two weeks ahead of schedule without any damage to the garden and patio area and with minimal disruption to the nursery school.

“We were very pleased with the professional approach of the Harmon renovation team on this project,” Hutchinson says. “They worked closely with our staff and tenants to ensure that things went as smoothly as possible.”

FUS’ board of trustees echoed the compliments in a letter sent to Harmon’s renovation team: “We are thrilled with the result! The work performed on our window wall was of excellent quality and completed in a timely and professional manner.”

For more information on Harmon Inc., call 763/287-4900.