Fiberglass Fenestration: A Durable, Sustainable, and Economic Alternative for Windows and Doors

By combining the benefits of aluminum, vinyl, and wood windows, fiberglass composites provide aesthetics and longevity for any environmental condition.
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Advertorial course provided by Pella® Windows & Doors
Barbara A. Nadel, FAIA


There are two primary methods of installing fiberglass composite windows in new construction and renovation projects: nailing fins and block frames with masonry clips or jamb screws.

Continuous perimeter nailing fins are used when construction methods permit window and door units to be installed from the exterior prior to the application of exterior cladding, such as lap siding, brick veneer and stucco.

  • The integral nailing fin design features a continuous fin, allowing the window frame to be integrated into the building's weather-resistant barrier.
  • The flush flange frame is designed specifically for replacement applications on stucco exteriors in arid climates, like those found in the southwestern United States. The flush flange allows for quick installation without removing the existing frame or damaging the stucco exterior.

Masonry clips or jamb screws are used when construction materials or sequence dictate that the window units be installed from the interior or after the wall system is completely constructed.

The block frame provides a variety of attachment and installation options. Windows can be installed in wood and steel frame openings using optional fins, or in masonry openings using installation clips or jamb screws. Block frames may also be used in window replacement projects without removing the existing frame or damaging the exterior.

  • Block frame with standard fin: Similar to the integral fin, the standard fin can be used with the block frame to provide a continuous attachment method that allows the window frame to be integrated into the building's weather-resistant barrier.
  • Block frame with offset fin: The continuous offset nailing fin is designed for use in new construction with stucco exteriors in arid climates, like those found in the desert southwest of the United States.
  • Block frame with installation clip: For new construction or window replacement where wall conditions or construction sequence require installation from inside the building.
  • Block frame with screw attachment: For new construction or window replacement where normal fin or tape installation cannot be accomplished because of wall conditions or construction sequence.

Summary of Fiberglass Composite Attributes

Fiberglass composite provides several important attributes that make it ideally suited for windows and doors in any location, climate condition or building type. When compared to other materials, it is more durable than vinyl or aluminum, exhibits the thermal efficiency of wood, and is an economic alternative to vinyl.

Additionally, fiberglass composite is energy efficient, and reduces sound transmission from the outdoors to indoor spaces. It is a sustainable material that consumes low embodied energy to produce compared to aluminum and vinyl.

As evidenced by the widespread use of fiberglass boats, fiberglass composite resists the corrosive effects of salt water, hot and cold temperature extremes, growth of mold and fungus, and can withstand long-term exposure to water, humidity, and moisture.

Due to the nature of its composition, fiberglass is strong and durable, and readily resists scratches, dings and dents that frequently occur on the job site, or in applications subject to daily abuse. Lastly, fiberglass composite is an economically competitive alternative to other fenestration materials.

Barbara A. Nadel, FAIA, principal of Barbara Nadel Architect, in New York City, frequently writes about design and technology. She is the author and editor-in-chief of Building Security: Handbook for Architectural Planning and Design (McGraw-Hill, 2004).


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Architectural Record
Originally published in June 2006