The design of all glass vestibule is unique to other glass structures, in that they include integrated walls, door portals, roofs and even canopies. At times, these systems are anchored to the base building structure, but just as often, they need to be designed to be self-supporting. Glass Vestibule door openings, in particular, can require self-supporting design based on surrounding materials and conditions, door types, electronics, and roof load.
In order to keep the structure as light and visibly transparent as possible, door openings with a simple door header and sidelites are often preferred to framed and clad portal structure. The design of the doors themselves can play a role in which components to choose for the opening:
Frameless glass doors
Frameless doors provide the lightest aesthetic overall, and can usually be anchored with simple patch fittings that attach to the header and sidelites. They do come with some important considerations, however:
- They require a gap of approximately 3/16” on all sides, which can allow air, water and dust inside. Options are limited for door sweeps and weatherproofing with acceptable aesthetics. See more about how to address this issue in our post on all glass vestibule conditioning.
- A frameless door and portal offers limited options for automated openers, typically requiring floor mounted equipment, which is more vulnerable to dirt and water infiltration along with other environmental issues.
Framed glass doors provide much better options for weatherproofing, but of course they are not as light aesthetically.
The glass doors at the portal on the CD Adapco headquarters building use simple patch fittings attached to the header and sidelites for a light aesthetic.
A floating header, which spans the door opening and anchors to the sidlites, can work with both door types, while providing a lighter look than a fully framed opening, with room for openers and associated electronics.
A simple header tube was used at this portal within the entrance wall of St. Joseph’s Drexel Library. Wiring for electronic openers, and strike plates for panic handles could be hidden with the header, to keep the opening relatively light and clean looking. The glass lites above the door opening are supported by floor to ceiling glass fins, and not the door opening itself.
The key design consideration in determining whether or not a structural portal is needed, is whether or not the opening must be self-supporting. In other words, when the door opening must support the load of the materials above (wall/framing/roof), a structural portal of one type or another (steel, aluminum, stainless steel, etc.) is needed to prevent loads from above from compromising the operation of the doors. Sizing the appropriate structural members is based on the width of the door opening, the weight of the load being supported, and the locations of where loads are being transferred to.
The framed portal at the Wistar Institute provides a dramatic stainless clad opening. This type of framed structural portal can provide the best weather seal at the doors, while also supporting structural loads above.
Initial design strategy recommendations
All glass vestibules are more about designing a signature look at the entrance than anything. Therefore, Bellwether recommends that the design process begin with conceptual aesthetic requirements, and then followed by an analysis of space, access (door opening size, electronics, etc.) and weatherproofing considerations. Once critical aesthetic and access requirements are set, a structural analysis can be undertaken to determine the options that will place the fewest limitations on each.