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Selecting a Skylight System

Performance, aesthetics, ease of installation and long-term value are top considerations for skylight systems for metal buildings

Extech Mar19 1

Using skylights to optimize daylighting in commercial buildings is referred to as top-lighting. In addition to providing electricity use cost-savings and energy consumption reduction, the benefits of top-lighting include increased productivity and sales, improved attendance and job satisfaction, and a positive affect on mental and physical health.

Top-Lighting Basics and Benefits

“Top-lighting can provide daylighting into any interior floor space area, a critical consideration for large floor plans,” notes the American Architectural Manufacturers Association (AAMA) Daylighting Basics online resource. “All of the newest U.S. energy conservation codes specify that many suitable buildings must now use skylights (and automated lighting controls) over specified portions of the occupied floor area because of the energy savings that are achievable in such buildings.” Operable skylight systems also support natural ventilation and provide a seasonal opportunity to help lower demands and energy costs to condition the interior space. Many metal buildings are not conditioned, making operable systems even more important to occupants’ comfort.

Glazing Considerations

The potential savings offered by skylights are dependent on specifying the right system for the application. Building orientation and the position of the installed skylight will determine how much solar exposure is available during the hours of operation. The glazing material also plays a key role. Glass, cellular polycarbonate glazing or fiber-reinforced plastic (FRP) are the most common glazing material choices for commercial skylight systems.

When thinking of existing metal buildings with skylights that are showing their age, it can be easy to picture old industrial facilities with FRP glazing that has deteriorated and discolored, which compromises both appearance and light transmission. Glass and cellular polycarbonate glazing maintain their appearance over time and are available with a range of coatings to enhance light transmission, impact resistance and thermal performance.

Framing Considerations

Beyond glazing, the skylight’s framing also helps prevent unwanted temperature transfer from outside to inside the building. Cost-effective and durable, aluminum is one of the most specified materials for manufacturing skylight framing members for commercial buildings.

Aluminum also is relatively easy to fabricate in factory-controlled conditions. In addition to rectilinear skylight configurations, aluminum can be shaped into creative geometric styles such as octagons, or stretch formed into barrel vaults and other curved shapes. High-performance anodize finishing or 70 percent PVDF resin-based architectural painted coatings usually are selected to enhance the skylight’s aesthetics and protect the aluminum framing. A baked enamel coating also may provide color options and good value for aluminum framing in less-demanding interior environments.

Performance and Safety Considerations

Because aluminum also is very conductive, the framing should be thermally broken to stop the heat transfer. Thermally broken framing includes either a polyamide thermal strut or poured-and-debridged polyurethane that fills the open channel in the extrusion and further blocks the path of conductivity.

For skylights with cellular polycarbonate glazing, expansion and contraction will occur in their metal framing, and gaskets may become disengaged if they do not have low-friction surface materials. This can lead to the glazing coming loose, which cause leakage, panel decay, and safety risks from compromised structural integrity. Skylights can be engineered and tested to resist snow loads, wind loads, dead loads and even hurricane force winds. However, be careful to heed the fall protection warning labels that remind people these systems are not engineered to support human impact or point loads.

Fabrication and Installation Considerations

Coordination between the roof contractor, skylight installer and skylight manufacturer is important to achieve a leak-free detail. Make sure the curb is of sufficient height to prevent water infiltration. When feasible, have the skylight manufacturer supply prebuilt curbs. These can be made with heavy-gauge metal and pre-insulated as an integrated, fully fabricated system. On steep slopes, ask the manufacturer to supply a cricket to shed water around the skylight.

For moisture that encroaches beyond the primary gaskets and condenses on the interior surface, skylights can be manufactured with gutter systems to keep the water from dripping into the finished space and its occupants. Be cautious to keep fasteners from penetrating the internal guttering to avoid future leaks. To avoid installation delays and extra costs, work closely with a skylight manufacturer that offers in-house engineering and fabricating.

A well-designed skylight system may look simple, but often is more complicated than it appears. Overlapping joinery, stainless steel pin connections, and guttering features give higher performance and more reliable installation. When property installed, a fully fabricated skylight system ensures quality control and performance as specified that maintains its appearance, functionality and value for years to come.

Jim Leslie is general manager of Exterior Technologies Inc. (EXTECH), Pittsburgh. To learn more, visit