Benefits, Challenges and Key Considerations for Commercial Skylights

Glass skylights were installed on this mixed-use residential project. Photos: EXTECH

Skylights optimize daylight, energy efficiency, occupant comfort and visual interest in new and renovated buildings. Whether one or many, fixed or operable, long-spanning or short-spanning, skylights are seen in every type of commercial facility.

As part of a daylighting design strategy, skylights provide consistent, long-exposure “top-lighting” to illuminate interiors while reducing electrical lighting demands. Beyond energy savings, research shows the benefits of top-lighting include occupant health and wellness, as well as increased accuracy, productivity, retail sales, student test scores and patient recovery times.

Maximizing these benefits, the building’s orientation, height, roof slope and position of the installed skylight determine the available solar exposure during the hours of operation. Daylighting analysis informs the skylight’s size, shape and placement. Early involvement between the building’s architect, skylight manufacturer and installer is critical to ensure specified performance and lasting effectiveness.

Common Applications

Commercial skylight installations range from airports and hangars to classrooms and libraries, from sports stadiums and equestrian centers to corporate corridors and manufacturing floors, from hospital lobbies and office conference rooms to shopping malls and restaurants.

Qualified contractors rely on multi-panel monumental skylights to meet the requirements of commercial, code-compliant projects. Commercial skylight configurations include single slope, ridge/double slope (A-frame), pyramid and extended pyramid/hipped ridge types.

Conceptual building designs often start with larger sizes and fewer skylights, but are value-engineered as more skylights in smaller sizes.

Glazing Choices and Light Transmission

Glazing materials for monumental skylights typically feature laminated safety glass, fiber-reinforced plastic (FRP) or cellular polycarbonate glazing (CPG). Laminated safety glass often is considered the best option for transparency to offer clear views and high visible light transmission. When diffused daylighting is preferred to minimize glare and associated eye strain, FRB and CPG present translucent alternatives.

This aquatic center features curved glass skylights.

CPG and glass do not yellow and will maintain their appearance throughout the window system’s lifecycle. With up to 70 percent light transmission, CPG usually surpasses FRP’s transmittance value. This means less material and fewer skylights may be required to achieve the same daylighting objectives. Not only can this lower initial costs, it can also save on future repairs.

Extending skylights’ durability and design, glass and CPG are available in a range of colors and coatings to enhance light transmission, impact resistance and thermal performance. Remember these attributes are interrelated — a change in one value typically changes the other values.

Framing Choices and Thermal Performance

Metal, particularly extruded aluminum, is the material of choice for framing commercial skylight systems. Aluminum is relatively easy to fabricate in factory-controlled conditions. Beyond the popular rectilinear skylight configurations, aluminum can be shaped into octagons, barrel vaults and other curved and polyangular shapes.

Extending the durability of the aluminum framing members, high-performance finishes include architectural painted coatings in almost any color and anodize finishes in metallic tones. These finish types also help minimize the care, maintenance and repair needed over a skylight’s lifetime. A baked enamel coating, while less resilient, may provide a large color selection and good value for aluminum framing in less-demanding interior environments. After the end of its use on a building, aluminum also is recyclable.

Aluminum is a versatile and durable material, but it also is highly conductive. Framing members should be thermally broken – separated and insulated to avoid heat transfer and energy loss. Skylights with high thermal performance help maintain the desired indoor temperature for occupants’ comfort, and contribute to the building’s energy efficiency and savings.

Indoor Air and Moisture Management

Fixed skylights are selected for most commercial applications with controlled HVAC. With greater attention to air quality in post-pandemic building re-openings, interest is growing in operable skylights to support indoor environmental quality and energy-efficiency with natural ventilation.

Proper ventilation also helps avoid excessive humidity and condensation inside the building. When the relative humidity is high indoors and low outdoors, condensation occurs on the interior of the skylight. This is especially common in cold climate zones and in tightly sealed buildings.

Condensation is more than an unexpected drip from above that damages furnishings and equipment. It also promotes the growth of mold and other microorganisms that negatively affect both building materials and occupants’ health. When bacterial growth infiltrates FRP glazing, a distinctly unpleasant odor also can permeate the space.

Skylights manufactured with gutter systems keep the water from dripping into the finished space and its occupants. Be cautious to keep fasteners from penetrating the internal guttering and to avoid future leaks. 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 pre-built curbs. On steep slopes, ask the manufacturer to supply a cricket to shed water around the skylight.

Structural Performance and Safety

Skylights, and the roofs they are mounted in, are engineered to resist snow, wind, seismic and dead loads, and, in some cases, hurricane-induced wind-borne debris impact loads. Skylights with CPG glazing are up to 250 times more impact resistant than glass and will not shatter or fracture. If CPG dislodges from its frame, such as due to an extreme weather event, it is lightweight and unlikely to cause damage.

If the glazing is broken or missing, water and pests also could cause damage to the building itself, along with presenting hazardous conditions to workers on the roof. Access to the roof and skylights should be restricted only to authorized individuals. Never walk on a skylight and always exercise caution near them. While skylights are tested to withstand environmental loads, remember they are not intended to withstand human impact or falling objects.

To promote safety, some building owners require protective guardrails or screens around the skylights. Operable skylights also may need to demonstrate resistance to forced entry. Additional test reports will validate structural integrity, fire ratings, thermal performance, condensation resistance and other performance criteria.

Schedule and Cost Considerations

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 often is more complicated than it appears. Overlapping joinery, stainless steel pin connections and guttering features give higher performance and more reliable installation.

Consider the associated expenses and time of transporting and lifting the skylight into place. A large, shop-fabricated skylight with hurricane impact-resistant, insulated glazing units will require a crane to install, but should take less labor and time on site than a field-assembled system. If labor is affordable and available, a field-assembled skylight with CPG glazing provides a significantly lightweight option.

To minimize costly corrections in field, seek a manufacturer with experience using BIM tools to visualize architectural renderings and adjust for interfacing or colliding materials. For a practical understanding of  interfaces, have the manufacturer provide a mock-up and review the installation sequence. Follow the manufacturer’s guidelines to ensure proper installation with a full warranty.

When property installed, a commercial skylight system delivers the intended appearance, specified performance and lasting value for years to come. The faster the skylight is installed, the more rapidly the other trades complete their work, the more quickly occupants enjoy their space and the sooner the owner will see a return on investment.

About the author: Jim Leslie is the general manager of EXTECH/Exterior Technologies, Inc., in Pittsburgh, leading the company’s mission to improve lives through innovation in daylighting systems, natural ventilation and other building envelope systems. Leslie has a bachelor of science in mathematics from Penn State University and is a member of the American Production and Inventory Control Society (APICS). He can be reached at jleslie@extechinc.com.

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