The Basics: Introduction to Curtain Wall Anchorage

Both glass curtain walls and storefront facades can be used to introduce more natural light to the interior of a building. While curtain walls are definitely more complicated to fabricate and install, they offer several design and structural advantages over storefront facades. As a result of this added complexity, curtain walls need to be attached to the structure of the building using specially designed anchors.

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A very brief history of curtain walls

The use of large glass display windows dates back to the mid-19th century, when manufacturers started to produce large glass panes at a relatively low cost. At the time, most buildings were designed with the exterior walls supporting the majority (or all) of the weight of the structure. The first storefront-style display windows, therefore, had to be embedded in cast iron structures that were able to support the building load. But the development of structural steel and reinforced concrete made it possible to support building loads with columns (rather than exterior walls), and therefore architects became free to design exterior walls that aren't load-bearing, using light materials like glass for exterior facades (in other words, curtain walls).

Curtain walls can be used in ways that glass storefront facades never could. For example, they can span multiple floors, handle larger wind loads, permit more natural light into the building, and they can be designed in complex shapes. But even though curtain walls don't bear any load from the building, they still need to be anchored to the structure to support their own dead load and account for factors like thermal expansion and contraction, water diversion, wind load, and seismic forces. The rest of this article will explain how various curtain wall anchors work.

Anchor type #1: F&T Clips

F&T clips are used to anchor the head and sill of a typical curtain wall system. The legs of the clips slide into the open ends of the vertical mullions. The F clips only have 1 anchoring leg and are used at the jambs, while the T clips have both anchoring legs and are used at intermediate verticals.

Anchor type #2: Windload Clips and Deadload Clips

When curtain walls span multiple floors they need to be anchored at the floor lines. This can happen at the slab edge, or a structural member such as an I-beam. Depending on the direction of the design team and engineers, the clips will either need to be slotted (windload) or through-bolted (deadload). If the clips are slotted, they allow movement while still resisting wind loading. This also allows the floors to move independently of the glazing system. For deadload or through-bolted clips, the movement must be allowed in the system through working splices.

Anchor type #3: F Perimeter

F perimeter is an aluminum extrusion that can be used at curtain wall jambs. These perimeter anchors help limit the deflection of the jamb and keep the joint sizes minimal.

Anchor type #4: Embed Anchors

Embed anchors are worth mentioning, even though the embeds do not actually attach to the glazing system members. Embeds are cast in place anchors that are set into the concrete while it is being poured. All types of system clips can be attached to them by mechanical and welding means.

Need help with your curtain wall design?

No single anchoring product is ideal for all applications. Variables like dead load, wind load, seismic forces, the size/shape of curtain walls, budget, lead time requirements, building codes, and more, all have an impact on what is the best anchoring solution. When in doubt, it's a good idea to consult glass and glazing experts.

MP Drafting specializes in producing complex drawings for glass and glazing systems with curtain walls of any shape, size, and connection type. Contact us today to talk about how we could help you select the right anchoring solutions and produce accurate shop drawings to streamline the fabrication and construction of your project.

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1948 - 1965

The Curtain Wall style refers to mid-20th Century buildings that use a prefabricated exterior wall sheathing system of glass and aluminium hung to their frames. The curtain wall, by definition, is a non-loadbearing enclosure that comes in a wide range of systems that can be made of virtually any combination of non-structural materials that meet insulation, wind-load, and aesthetic requirements. In this case, however, the Curtain Wall style refers to buildings that utilized a glass and panel system for a majority of the exterior facade.

The use of such technology dates back to the 1909 Boley Building in Kansas City, which is credited as the first building to use an all-glass exterior wall system. However, it was not until post-WWII when advancements in building technology allowed these systems to become widespread.

The first major example of the style was the Equitable Savings & Loan Building in Portland, Oregon executed by architect Pietro Bellushi in 1948. As the world's first fully enclosed air-conditioned building, this sleek 12-story structure quickly set the pattern for many post-war skyscrapers and small-scale office buildings.

The curtain wall system is comprised of a repetitive grid of vertical extruded aluminum mullions and horizontal rails. Panels called spandrels divide the large expanses of glass horizontally to hide the floors and ceilings. These spandrel panels can come in a variety of materials. Early spandrel panels were made of heat-strengthened opaque glass fused with colored ceramic. The Pittsburgh Plate Glass Company manufactured the glass panels under the trade name "Spandrelite," and offered eight standard colors. The Libbey-Owens-Ford Corporation sold sixteen color options under the "Vitrolux" brand. Colors ranged from "Hunter Green" to "Cavalier Red," to "Charcoal" and "Suntone" Yellow. While customers could order custom colors, typical tones found in the Northwest included turquoise, pink, and blue. Later, spandrels were available in other materials such as composite metal panels containing lightweight insulation cores, precast concrete panels, asbestos panels, porcelain enamel, tile, masonite, thin stone veneer, and plywood panels (a material particularly popular in the Pacific Northwest). One of the main providers of curtain wall systems here in the Northwest during the 1950s and 1960s was Fentron Industries.

Considered suitable for virtually any size commercial, government or institutional building, the Curtain Wall style became widespread by the early 1950s. Many post-WWII buildings of varying styles also incorporated curtain wall systems into some facades but are not considered Curtain Wall style unless the majority of the visible facades are so constructed. The modular construction method used to construct the Curtain Wall style made it economical and popular for a time. However, by the late 1960s, it was being replaced with a smoother or Slick Skin application.

Washington State Examples

Washington Water Power Co.,
Spokane - 1959

Logan Building,
Seattle - 1958

1007 Washington Building,
Olympia - 1959

Blue Cross Building,
Seattle - 1959

Puget Power Headquarters
Bellevue - 1956

Sunset Life Insurance Co.,
Tumwater - 1956

Contact us to discuss your requirements with Aluminum Curtain Wall Manufacturers. Our experienced sales team can help you identify the options that best suit your needs.

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