Maintenance
At the beginning of the project, the design professional must determine the building owner’s expectations regarding service life and maintenance of the replacement skylight system. When maintenance or cleaning is required, safety systems must be implemented to avoid any unnecessary loading on the glass, as well as prevent individuals from impacting or falling on the glass. Safety systems should be considered given relevant requirements of the Occupational Safety and Health Administration (OSHA) and might include a combination of signage, barriers, guardrails, fall protection anchors, or other features.
The design professional may consider providing glass designed to be walkable (using ASTM E2751, Standard Practice for Design and Performance of Supported Laminated Glass Walkways), for large skylights that cannot be cleaned from the adjacent roof surfaces or skylights that will require frequent access for maintenance and cleaning. These can include glazing systems that rely heavily on sealant (e.g. point-supported systems with butt-glazed joints), lack redundant drainage features (e.g. internal gutters), or incorporate low-sloped surfaces.
Construction logistics and building operations
It is important for the design professional to consider how the replacement skylight will be erected by the construction team. Limitations may include site access for materials and equipment (e.g. elevators, ingress/egress doors, exterior crane and lift access, etc.), physical space on the site for material laydown, space for worker and equipment mobility, and other unforeseen conditions. These can affect the methods of construction, including which portions of the skylight can or may need to be preassembled versus stick-built (i.e. built in place). The structural capacity of the existing roof can also affect the location of the material and equipment laydown and storage areas, which may need to be located over building columns. Note manufacturer production and shipping capabilities, as well as the space and access constraints previously mentioned, can affect the extent to which skylight components can be preassembled. The design professional must also consider whether the building is actively occupied and if the building owner prefers to limit tenant impacts and access through the building.
Other design considerations
Beyond the topics covered in this article, a skylight replacement design may also impact design decisions related to acoustics, fire safety (e.g. related to automatic fire suppression systems), and falling ice and snow. These topics should be addressed by appropriate members of the design team in coordination with the designer of record.
Conclusion: Best practices
The following items summarize some best practices to consider when establishing a design agenda at the commencement of a skylight replacement project:
Identify the building owner’s motives for replacing the skylight and key expectations regarding overall system design, cost, serviceability and maintenance, and performance goals;
Visit the project site to study how the existing skylight system is performing, conduct field investigations, and identify constraints related to the existing construction, including building management and operational requirements in addition to access and constructability constraints;
Obtain the original building design documents to understand the structural capacity of the existing building structure, the makeup of the existing skylight support system, and the interior space conditions. Review the operating conditions with the building owner and building engineer in the event they differ from the original design conditions;
Reach out to the manufacturer of the basis of design replacement system to establish a proof of concept based on realistic expectations of the manufacturer’s capabilities, performance characteristics of commercially available systems, and available system features; and
Review the jurisdiction-specific code requirements related to the design and implementation of the replacement skylight.
Authors
Sarah Rentfro, PE, is senior consulting engineer with Simpson Gumpertz & Heger in Washington, D.C. Her expertise encompasses building enclosure design, consulting, investigation, and construction phase services with a focus on integration of complex building enclosure systems and building science. Rentfro can be reached at sbrentfro@sgh.com.
Kayla Salmon is a building science consultant at 4EA Building Science in Seattle, Washington. She specializes in building enclosure engineering and consults on new and existing structures. Salmon has contributed to several projects nationally, involving new design consultation, forensic investigation, historic preservation, and construction administration. She can be reached at kaylas@team4ea.com.
John Karras, PE, is an associate principal with Simpson Gumpertz & Heger in Washington, D.C. His expertise encompasses building enclosure design, consulting, investigation, and construction phase services including projects related to fenestration, roofing and waterproofing, and exterior wall systems. He can be reached at jnkarras@sgh.com.
