1000 Maine at the Wharf in Washington, D.C., features six different glazing configurations, including a two-toned terracotta unitized curtainwall system.

Glazing is an integral part of a building’s façade, giving occupants access to the outside world while protecting them from its elements. However, there are many differences between the various glazing types which impact performance and aesthetics. It’s important for glazing contractors to be aware of these differences and how they can impact installation.

Curtainwall vs. Window Wall

A curtainwall is a glazing system that runs past the floor slabs, essentially hanging from a building’s front structure, whereas a window wall system sits between each floor’s structural elements. According to Crawford-Tracey Corp. owner Ray Crawford, curtainwall configurations are usually 4 to 5 feet wide and 14 feet in height or taller. Window wall panels are often smaller since the system does not have to span the area in between floors.

Russell South, project manager for Giroux Glass in Los Angeles, says storefront systems, which are used for first floor applications, typically are 10 to 12 feet in height. Window wall usually is installed beginning with the second floor with a storefront system on the ground floor. Curtainwall systems can be used on any floor.

Storefront and window wall systems drain water differently than curtainwall. South says that on a curtainwall system, the water drains out of each individual lite so that each horizontal on a multi-span building drains water. For storefront systems, the water goes into the horizontal before being transitioned down the vertical and out the sill at the bottom.

“When you’re doing more than one floor you don’t want to use storefront because it will take on a lot of water and you don’t want all that water running down the verticals,” says South “Also, since curtainwall is more robust, it works better for windload issues because it has a deeper mullion.”

Curtainwall also includes pressure plates along the mullions and longer mullion depths, often assembled with shear blocks, due to the higher design pressures associated with these systems. Window walls do not require pressure plates and are assembled with screw splines rather than shear blocks.

YKK AP field technical services manager Bart Harrington says that the installation of window wall products is much more like the installation of a storefront versus a curtainwall system. While some window wall systems have slab edge covers to give it the appearance of a curtainwall system it won’t be as streamlined in appearance as a curtainwall.

“Since a window wall system is sitting in between the floor slabs the slab edge cover will create a significant reveal at the floor slabs,” says Harrington. “This isn’t a design element of curtainwall systems, which are much sleeker. It’s less apparent where the floor slabs are [located.]”

Curtainwall systems typically are pressured equalized, meaning the air pressure inside each individual zone is equalized with pressure on the outside of a building so gravity can pull water out of the system continuously. With a window wall system there is no pressure equalization, so while gravity may be pulling water to the bottom of the system, it requires a water head in the flashing at the bottom of the system.

Storefront and window wall typically are less expensive than curtainwall. One aspect that can contribute to the cost difference is that there are more glazing contractors capable of installing multi-floor window walls.

“This opens up competition to a wide variety of glazing contractors and the competition can help keep costs down. The more sophisticated a project, the fewer the contractors that are able to bid it,” says Harrington.

To read the full article, which originally appeared in the December 2019 issue of USGlass magazine, click here.