Need-to-Know Information: A Glazing Systems Checklist
By Stewart Jeske
Our company recently exhibited at the 2023 American Institute of Architects
Conference on Architecture in San Francisco. We came up with the essential items that we wanted to communicate to architects, which became a “Glazing Systems Checklist for Architects.” It includes the following:
Building Structural Movement
• 95% of contract documents reviewed require accommodation of vertical structural movement.
• Show where and how much building structural movement to be accommodated.
• L/360 does not work vs. glazed system manufacturer limitations.
• Manufacturers’ standard details allow for less than ¼ inch structural movement.
• Sealant joint formula = double (movement + thermal) minimum.
• Who is responsible for the design of sealant joint for movement?
Storefront
• Storefront vertical span range is 9 to 12 feet; more horizontals = better span length.
• Architectural details are typically deficient showing shimmed head joints allowing for zero structural movement.
• Make sure details show a receptor head.
• Receptors only accommodate about ½ inch vertical structural movement-actual structural movement may be more.
• Typically, anchors are through the glazing pocket and usually require straps back to the structure.
Curtainwall
• Spans are 10 to 25 feet with deep systems.
• Taller spans at stairs require deeper systems or wind girts to support.
• Two-part open shapes require more steel
reinforcement vs. tube shape mullions.
• Manufacturer stock lengths (~ 22-24 feet) require ugly/expensive structural splice joints if not planned well. Longer stock lengths may require longer lead times.
• Watch for thermal bridging at floor connections. Use anchor systems with thermal breaks.
• Design sealant joints at head details for building structural movement.
• Long-span jamb mullions may require movement joints > ½ inch.
Glass Railing and Windscreens
• Windscreen applications typically are too much load for standard railing shoes.
• Glass guards under the 2018 IBC require a cap; ½-inch monolithic glass is usually unacceptable.
• Laminated glass is required except over non-walking areas.
• ICC AC439 testing is acceptable.
• Windscreens and glass guards for roofs cannot be installed over the roofing membrane.
• Too many shims mean wobble in the railing.
• Ensure sufficient concrete curbs for anchoring.
Corner Modeling
• 3D structural modeling should be performed.
• Short return curtainwall and storefront sections may get pulled out by windloads and require additional steel reinforcing.
• Minimum bites at corner mullions require checking by specifications for in-plane movement created by windload at the corners.
Vertical Sunshades
• Deep cap extensions (12 inches or more) will add in-plane windloads to glazing systems.
• Specs typically limit in-plane movement to 1/8 inch.
• Manufacturers have not designed systems to handle these in-plane loads.
• Storefront systems with fill plates are not usually capable of sunshade support.
This list could form the basis of important discussions with architects during any stage of a project, but preferably in the initial design stage.
Stewart Jeske is president and owner of JEI Structural Engineering in Kansas City, Mo.
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