Fiberglass Clears Commercial HurdlesJanuary 2, 2012
Jaime Marrero, Pultrusion Sales Manager, Graham Architectural Products
Selecting a window system for use in new or renovated commercial and institutional buildings has typically gravitated to metal-framed or reinforced windows to provide the strength necessary to meet AAMA CW and AW performance classes. In the last five years, however, fiberglass window systems have rapidly gained attention and are being increasingly specified and installed more and more in retail facilities, offices, schools, colleges, condominiums, apartments and many other buildings.
Commercial buildings in the U.S. are said to consume 30 percent of the energy used in the country each year. This sector is thus a focal point for energy efficiency improvements embodied in the latest evolution of building codes.
In particular, the 2012 International Energy Conservation Code (IECC) calls for window U-factors of 0.32 to 0.35 in all but the extreme southernmost climate zones. Under the 2012 I-codes, these U-factors apply to commercial as well as residential buildings as, for the first time, the International Residential Code (IRC) and the commercial-oriented International Building Code (IBC) both defer to the IECC for energy efficiency requirements.
Because fiberglass has inherently low thermal conductivity, the profile acts as a continuous thermal break. Thus, a fiberglass window frame rather easily meets these 0.32-0.35 U-factor goals. As a result, the low thermal conductivity helps to reduce condensation on frame surfaces, which can mitigate mold and mildew issues in high-rise construction.
A second major reason for the increasing acceptance of fiberglass fenestration in commercial applications is its strength, which allows very large windows (with sealed insulating glass units as thick as 1½ inches) to be made without reinforcing.
The latest I-code referenced version of the North American Fenestration Standard, or NAFS (AAMA/WDMA/CSA 101/I.S.2/A440-08), sets minimum (“gateway”) design pressures for LC, CW and AW class windows of 25, 30 and 40 psf, respectively, with the option of qualifying for higher performance classes at design pressures up to 100 psf for LC and CW rated products, or at any higher pressure for AW products, limited only by practicality and cost. These products must meet structural test pressures of 1.5 times the design pressure. For AW class products, no member of the window frame can deflect more than one 175th of the length “L” of the member(expressed as L/175) and must also pass forced entry and deglazing tests.
Thin-walled pultruded frame profiles with engineered cavities can meet these requirements, providing enough strength due to the inherent properties of the material to bear the glass load. Further, they are commonly configured with added insulation inside the frame cavities, boosting the overall thermal resistance.
In addition to the thermal and structural aspects, there are several characteristics of fiberglass composite windows that have contributed to their increased use in commercial and institutional buildings. These include:
- Design flexibility. Fiberglass can cost-effectively be fashioned into complex shapes, and its high strength-to-weight ratio also enables large window openings common in commercial settings.
- Durability. In addition to its strength, certain factory-applied finishes render fiberglass composite almost indestructible and long lasting. Further, it will not corrode or rot. Fiberglass particularly resists environmental damage caused by corrosive salt air.
- Impact resistance. Fiberglass composite withstands major impacts without deformation, especially in cold weather. Impact resistance is particularly important on the job site during installation, when dents and damage may inadvertently occur.
- Thermal performance. Fiberglass composite can withstand a wide range of temperature extremes, encompassing heat up to 200°F and cold down to -40°F. In particular, because fiberglass composite windows are made using thermoset resin, they can be used in hot climates and can be painted with dark, heat absorptive colors, even in high sun exposure applications, without softening and risking deformation.
- Thermal expansion. Fiberglass composite has a very low coefficient of thermal expansion (CTE) that is very similar to that of glass. Consequently, it moves very little as the weather changes, readily maintaining frame-to-glass seal integrity. This reduces the potential for air infiltration and water penetration, major causes of U-factor deterioration and water damage.
- Low CTE also translates to dimensional stability through all types of weather. As natural ventilation is required to meet green building requirements and general human comfort, operable windows are becoming more common in commercial buildings. Because of the stability of fiberglass, these operable windows are unlikely to jam or become difficult to open, whether for ventilation or cleaning and maintenance.
- Sustainability. Fiberglass composites have relatively little embodied energy relative to that used to produce the product. Further, their production produces no Volatile Organic Compounds (VOCs) that contribute to air pollution. They also exhibit low resource utilization impact, as the primary ingredient is readily available silica sand.
- Acoustical performance. Finished fiberglass fenestration units provide serve as effective sound barriers between outdoor and indoor spaces.
The net result of all of these characteristics is that fiberglass composite windows offer an alternative for commercial buildings of all types – one that meets the performance challenge of energy efficiency combined with structural performance.