Volume 35, Number 9, September 2000

Alleviating the Labor Crunch

Unitized Curtainwall Systems Help Keep Projects on Budget and on Time

by Heather West

Contractors and construction managers want to keep labor costs low while meeting tighter and tighter installation time-frames. Building owners and managers want to keep building tenants comfortable while keeping maintenance and energy costs low. Architects want to design elegant structures with larger and larger windowscapes.

High performance curtainwall systems can address all of these desires. Involving the curtainwall manufacturer early in the design process will help keep the project on budget and on time.

wpe15.jpg (4939 bytes)The AEFA’s two-story interior walkways, designed with unitized curtainwall, allow lots of sunlight all year.

 Labor Lag

“Early involvement among the curtainwall system manufacturer, glazing contractor, general contractor and architect is a necessity to keep projects on track,” said Steve Fronek, Wausau Window and Wall Systems vice president. “With a 3.5 percent unemployment rate, the construction industry is suffering from a shortage not only of qualified labor, but labor in general. This favors a movement toward pre-assembled, pre-engineered, and pre-fabricated systems. There are often too many variables associated with field labor. The experience and availability of labor forces is limited in many areas. It’s also expensive in terms of both time and money. The faster we can close up the building’s exterior skin, the faster that building can open for business,” he added.

A unitized curtainwall design allows for system components to be fabricated and assembled in panelized frames (units). The panelized frames usually span vertically, from floor-to-floor. The width of the system’s horizontal span is dependent on weight and glass loading stresses on the aluminum framing and transportation capabilities.

wpe16.jpg (5034 bytes)Unitized curtainwall systems accommodate aesthetic options such as the AEFA’s granite panels.

 Sound, Seismic, Sun

Unitized curtainwall systems reduce dependence on field weatherseals and can accommodate building dynamic movements without placing unnecessary stress on glass, sealants or other infills. Performance characteristics of unitized curtainwall designs include enhanced water resistance and air performance. Acoustic, seismic and thermal performances are important factors when engineering a unitized
solution.

When addressing acoustical considerations, blocking low frequency noise requires more mass than blocking high frequency noise. High frequency noise, however, passes through small leaks easily, and unitized systems can be designed with a variety of glass types, thicknesses and air spaces to meet the building specifications.

With the adoption of the UBC-1997 Model Building Code, seismic forces and movements are of increasing concern. Thermal performance is also of primary importance, ensuring a limited amount of undesirable heat gain or loss under all seasonal climatic conditions.

For instance, while sunshades can help keep the sun’s heat off of the building, as well as enhance the building’s architectural beauty, they, along with shading controls, are also a growing trend in curtainwall designs.

“It’s usually a mistake if these shading elements aren’t included as part of the curtainwall design. If they are to stand up to weather and structural performance, they need to be fully engineered into the overall system, not added as an afterthought,” warns Fronek. “There are so many factors to take into account, such as the amount of load the sunshade has to support, movement and installation sequence. Unitized systems often offer the best integral solution.”

 Accommodating Aesthetics

In addition to its performance advantages, unitized systems can accommodate a variety of aesthetic options including more pronounced sight lines and a variety of architectural elements such as granite panels.

Nearly 4,000 employees will occupy the new American Express Financial Advisors (AEFA) Minneapolis headquarters by mid-October of this year. The simple, yet elegant, 30-story building is one example of a structure which relies on a unitized system, incorporating Cold Spring granite with tinted glass.

As a design/build project, representatives from Opus Northwest (OPN) the project’s developer and design-builder, AEFA and architect HKS Inc. all worked together to plan the building’s exterior. Because Opus knew the glass curtainwall would play a significant role in the building’s appearance and functionality, glazing contractor Harmon Ltd. was brought on to the project shortly after discussions began. As a major supplier on the project, Wausau Window and Wall Systems provided unitized curtainwall panels, shipped from its facilities in Wausau, Wis.

In total, more than 5,500 5- by 15-foot units were required for AEFA. Some units weighed in excess of 2,500 pounds. Shipments of 30 to 40 pre-assembled units were sent out several times a week.

Installation for the AEFA curtainwall system took less time than anticipated, finishing in six months instead of the scheduled eight.

Fast Finish

Pre-glazed units typically are off-loaded at the project site using the main construction crane. Normally, they are lifted to the roof or the floor above their installed position where they are stored and organized for future distribution. Most curtainwall units must be crane or winch-lifted into place from the outside of the building. Using this method, little handling is needed for each unit, which decreases the number of opportunities for a mishap and saves time overall.

Since the units are erected by stacking individual panels vertically and horizontally, a four-way stack-joint design results. For any successful project, special materials and careful applications must be of top importance as this is the system’s primary seal and is critical to its life-cycle performance.

Heather West manages public relations for Wausau Window and Wall Systems and Harmon Inc.


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