August 30, 2018
by Steven Gille
More than ever, it has become the responsibility of specification writers to ensure curtain wall products’ performance, testing, and installations are defined in order to meet project requirements. A properly installed, field-assembled stock length curtain wall can meet industry leading performance standards, and support continued construction challenges with regard to availability of qualified labor, as well as fast-track project schedules.
The construction industry is currently challenged by a labor shortage, while being pressured to reduce costs and compress project schedules. Field-assembled curtain walls may seem counter-intuitive in these conditions, but in fact, there may be some benefits to this method.
After the most recent recession concluded in 2011, the commercial construction market reported an increase in starts. With the exception of 2015, double-digit growth percentages continued through 2016, moving to single-digit growth in 2017. In 2018, starts began trailing slightly behind last year’s annual average pace, according to Dodge Data & Analytics. Reflecting the cyclic nature of construction starts, the forecast downturn currently is projected to begin in 2019, and followed by predicted improvements starting in 2022.1
The top five metropolitan areas for commercial construction starts are New York, Los Angeles, Dallas, Washington, D.C., and San Francisco, as of February 2018. Until April 2018, office, retail, and large hotel construction markets showed the highest percent of growth, noted Dodge Data. A historic review of Dodge Data shows a steeper decrease in construction starts for large projects (those with 10 floors or more), compared with low- to mid-rise projects during market downturns.2
While the average pace for construction starts may be slowing, the need for qualified labor is higher.
The U.S. Chamber of Commerce notes filling available jobs within the construction industry remains a key issue. More than 90 percent of contractors are concerned about finding skilled, qualified labor and expect problems to worsen. In contrast to their worries regarding labor, contractors have high confidence in the market’s ability to provide new business for the next 12 months through June 2019. Nearly all (96 percent) of the contractors report high or moderate confidence in the demand for commercial construction.3
In Glass Magazine’s 2018 Top 50 Glaziers report, 67 percent of respondents cite higher sales, 57 percent report increased bid levels, and 33 percent are experiencing greater competition for projects. New construction represented 84 percent of their projects, and their best markets were office, multifamily, and education. Again, labor was a top concern for glazing contractors. More than half (53 percent) reported difficulty in finding qualified workers and 36 percent indicated it was about the same as the previous year. The most challenging positions to fill included:
As commercial contractors continue to face labor shortages and search for qualified workers, their already fast-paced schedules for new projects can compress and costs can increase. The U.S. Chamber of Commerce found commercial contractors
turn to alternative construction solutions such
as prefabrication and modularization to create
more efficient jobsites (89 percent), increase labor productivity (85 percent), drive cost savings
(58 percent), and provide a competitive advantage
in the marketplace (51 percent).
Across all regions, concern over the cost of hiring skilled labor has remained consistent throughout the past year with 64 percent of contractors expecting these costs to increase by September 2018. Helping counter these costs, nearly two-thirds (63 percent) of commercial contractors surveyed showed moderate to high demand for prefabricated and modular building materials.5
Factory assembled vs. field-assembled
It may seem counter to the prefabricated and modular trends to have regional and local glazing contractors buying stock length materials from curtain wall manufacturers for field assembly. On closer inspection, this construction solution follows the same pursuit for efficiency by minimizing longer lead-times and higher shipping costs on unitized products, and allowing just-in-time response to changing schedules.
Extruded aluminum is the industry standard for both factory-assembled unitized and field-assembled stock length curtain wall systems. Thermal breaks and barriers are used to separate the exterior and interior aluminum surfaces for improved thermal performance (U-factor) and condensation resistance. Insulated glass units (IGUs) and architectural finishes offer numerous options to enhance the overall system performance, durability, and aesthetics.
Additional design options for curtain wall systems may include:
Used for high-rise building applications, unitized curtain wall systems are fabricated and assembled by the manufacturer into units spanning one or two floors, and are often installed by large national glazing contractors. These units are shipped to the contractor and installed using a construction crane. The factory assembled curtain wall often takes several weeks or months for delivery. The shipping, equipment rental, and licensed operators also are significantly more costly than field-assembled systems and staff.
Best suited for low- to mid-rise buildings, shop or field-assembled curtain wall systems often are installed by local and regional glazing contractors. The manufacturer provides these systems as “knocked down” or stock lengths. Knocked down systems are cut and machined by the manufacturer. Parts can be sent from the manufacturer by like type or grouped by item. Stock length, or “stick,” systems are aluminum extrusions sent in lineals, requiring the glazing contractor to cut and machine them in their shop or at the jobsite.6 A major benefit of knocked down and stock length systems is the flexibility they provide the installer to perform functions in their shop or at the jobsite depending on the project’s timeline, onsite space availability, and labor type and availability.
To retain qualified staff during downtimes, some glaziers prefer to have their employees handle as much of the curtain wall preparation and assembly as possible. Stock lengths typically ship in days or weeks, and at a lower freight cost than a factory assembled system’s large units. The glazing contractor assembles the curtain wall, and it is typically installed using a lift owned by the contractor. Managing the assembly, equipment, and labor locally provides glazing contractors with greater flexibility in meeting projects’ dynamic construction schedules.
Performance as specified
Regardless of whether the curtain wall will be provided as unitized or as stock length for field assembly, the manufacturer is responsible for designing and testing the product to rigorous industry standards. Detailed installation instructions in the form of manuals or project-specific shop drawings are critical to a successful installation.
The American Architectural Manufacturers Association (AAMA) 501, Methods of Test for Exterior Wall, is the first and most reliable indication for specification writers seeking to ensure curtain wall products meet a project’s required performance. Following AAMA 501, curtain wall manufacturers provide specifiers with test results or full test reports for review, which validates the curtain wall products perform as designed and in substantial accordance with the test procedures described in AAMA 501 and referred in ASTM standards.
Below is an example of an AAMA 501 testing sequence manufacturers would follow to validate their products’ performance for a typical stock length curtain wall used for low- to mid-rise projects. If project-specific testing is required, it is important to identify the test and sequence in the specification. Design professionals can refer to AAMA 501 for complete descriptions of all mandatory and optional tests and sequencing.
Additional testing can include acoustics, condensation resistance, U-factor, ballistic, hurricane resistance, blast mitigation and other performance criteria. Industry standards and procedures describe requirements, including sizes and quantities, for each application. These requirements must be clearly described in the specification. The performance-based testing described earlier is completed at an independent, certified curtain wall testing facility. Additional field testing,
such as air and water, as well as non-typical field testing (e.g. acoustics), may be specified based on project requirements.
Installation methods and considerations
After successfully passing the testing outlined above, the curtain wall manufacturer develops a detailed installation manual outlining the proper frame fabrication, assembly, installation, and anchorage, glazing, and watertight sealing into the opening. Each test provides necessary information regarding performance of the installed curtain wall. For example:
The glazing contractor and ideally, the specifier, should be aware and involved with the manufacturer’s testing of the installed curtain wall to ensure project-specified performance and function. The curtain wall manufacturer can assist in noting critical installation techniques, seals, and anchorage in order to meet the performance requirements outlined by the project’s specification writer.
Engaging a curtain wall consultant will provide even greater insight for the system’s performance and help align expectations across the project team. This also may reassure the specifier the manufacturer’s system can and will meet the performances outlined for the project.
The glazing contractor’s knowledge of field installation techniques can further enhance the curtain wall system’s usefulness and value. Consulting with the project’s specification writer, the manufacturer and glazing contractor may be able to make recommendations to meet the specified requirements, while saving time and associated costs.
With glaziers and field installation personnel in short supply, early collaboration between the specification writer, curtain wall manufacturer, and glazing contractor can offer construction solutions optimized for the project’s available labor, timeline, and budget, while ensuring performance as specified.
1 For more information, click here.
2 Read “Construction Market Forecasting Service Sneak Peek: The Next Five Years,” published in May 2018 by Dodge Data & Analytics here.
3 For more information, click here.
4 Find out more here.
5 Get more details here.
6 A lineal is a linear (straight) section of material, usually measured in feet. A typical length is 7 m (24 ft).
Steven Gille is a product development engineer at Tubelite. He draws from more than 30 years of experience in designing, engineering, testing, and developing curtain wall, storefront, entrances, and daylight control systems. He works closely with specifiers, architects, glazing contractors, and consultants to assist with product information and selections and new solutions. He may be reached at firstname.lastname@example.org.
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