What’s the Difference?

Weighing in on Window Wall Trends and Developments

By Ellen Rogers and Jordan Scott

All construction projects aren’t created equal, and the same goes for the different types of glazing system options. Take, for example, curtinwall and window wall. They each can offer similar looks and aesthetics, yet in some cases, window wall can be a cost-effective alternative to curtainwall.

Window wall units traditionally are manufactured and glazed in the shop, which can minimize the need for labor-intensive, on-site installation.
Given the increasing employment and labor challenges the contract glazing industry is facing, this can be a most attractive benefit to the industry.

A recent report from University of Toronto’s Building Tall Research Centre and the Residential Construction Council of Ontario (RESCON) titled “Window Wall and Curtain Wall: An Objective Review,” provides an indepth comparison of window walls and curtainwalls, looking at each cladding system’s strengths as well as their applications.

According to the report, construction costs vary in practice, but a typical window wall can cost nearly half as much as a typical unitized curtainwall to install.

“Reasons for the lower cost of the window wall include fewer major
hoisting equipment needed during installation, simpler components for
manufacturing and the lack of a requirement for it to be structurally engineered to be self-supported.”

Several industry companies also agree that they’re seeing increasing interest in window wall products, particularly in mixed-use applications.

Curtainwall vs. Window Wall: Which Should You Use?

A 2017 study conducted by the University of Toronto’s Building Tall Research Centre and the Residential Construction Council of Ontario (RESCON) investigated the advantages and uses for both window wall and curtainwall. The comparative analysis of the two materials used metrics of thermal performance, air tightness, water penetration, condensation, constructability, maintenance and cost. Here’s a look at some of the key findings:

  • Window wall is more suitable for residential construction as it accommodates features such as balconies, operable windows and suite compartmentalization (i.e., contains odors, noise and air movement within a single unit) compared to curtainwall, which is more appropriate for commercial buildings. Window wall also has significant advantages for constructability, cost, and maintenance.
  • While the intrinsic properties of curtainwall and the way it is attached to a structure does have some advantages, a well-designed and properly installed window wall system can perform equally or better based on the studied metrics, and at a lesser cost.
  • Best practices for the design and installation of window wall cladding have advanced to achieve better performance including reduced thermal bridging to the concrete structure; less conductive window wall frames; rain screen design to collect and drain any penetrating water. Construction mock-ups and field testing have become more commonplace and further contribute to improving water penetration and/or air filtration.

Patrick Marquis, one of the report’s authors and a master’s of applied science candidate at the University of Toronto’s Department of Civil Engineering, noted a few caveats to the report.

“More analysis is still required to fully compare the systems. A comparison should be conducted with mockups of the systems to corroborate the Morrison Hershfield modeling results. In many contexts the systems are not as interchangeable as perhaps implied from the comparison. They are not direct competitors,” says Marquis. “The report is a review paper, with some added commentary. None of the modeling referenced in the report were conducted by the Building Tall Research Centre.”

For more information or a copy of the report visit http://buildomtall.utoronto.ca/

Cost and Labor Saver

Faced with the challenge of a dwindling qualified workforce, many contract glazing firms are exploring alternatives that can help improve the labor situation. One such option has been to work more with pre-glazed systems to reduce the need for on-site labor.

“A key attribute of window wall systems is the ability to install and glaze
from inside the building,” says Greg Galloway, ProTek brand manager, with Austell, Ga.-based YKK AP. “This attribute is enhanced by the recent trend of pre-glazing, which further shortens installation time. Aesthetically these systems look a lot like curtainwall, with front set glass that improves energy performance and lowers exterior maintenance costs.”

He adds that while commercial buildings, such as office buildings
and hotels, traditionally have been built with curtainwall, window wall
has emerged as a preferred system for mixed use buildings—those with retail and businesses on the ground floor and residential units on the rest of the building, typically 15 to 30 stories.

“Window wall installs quickly and has a noted cost advantage over curtainwall. Window wall also compartmentalizes issues and confines them to a single floor,” says Galloway. “These attributes can help make residential units affordable while offering other benefits.”

Some of those benefits include a shorter construction cycle since window wall allows drying-in by floor, compared to drying-in by elevation with curtainwall, as well as additional cost savings since fire-stops between
floors are not required.

Product Details and Specifics

In addition to the cost-saving benefits, there are number of other differences when it comes to deciding between window wall and curtainwall. Mark Hiscock, sales manager with Graham Architectural Products based in York, Pa., says curtainwall will provide
more of a complete glass appearance whereas window wall will provide a
ribbon window look.

“A lot of our window wall work is design-driven. The owner, architect, etc. likes the look of ribbon windows with the slab edge cover,” he says. “A lot of these products are going into mixed-use, residential towers where they like operable windows.”

Hiscock points out that window wall allows for the integration of slab edge covers for a complete system, as well as the incorporation of terrace doors and hidden sash vents to allow for consistent sightlines from fixed to vent windows.

“The vents are much larger than in the past and, in most cases, require
ADA compliance while still meeting high air, structural and water performance,” he says. “This combination of criteria requires extensive testing, leading to redesign and exploration of alternate hardware options.”

Craig Carson, regional preconstruction manager with Alliance Glazing
Technologies in Littleton, Colo., points to the example of a mixed-use condo or apartment, which has a smaller floordeck-to-deck height between the floors, somewhere between 9 feet, 9 inches and
10 feet 6 inches, allowing for the use of window walls to fit between the top of the floor deck and span to the bottom of the floor above (ceiling).

“This is for two reasons: it eliminates the need for fire-stopping and smoke seal at the slab edge, such as in a curtainwall installation. It also helps reduce noise transfer between the floors,” he says.

He adds that the shorter height will allow for a shorter depth system
that’s also enhanced since the typical residential unit is based on 4-foot
centerlines for the vertical mullions; commercial buildings are typically
5-foot centerlines.

According to Galloway, one of the biggest window wall trends has been
the shift from inside glazing on the jobsite to pre-glazing, which he says
is being fueled by a couple of factors.

“It’s increasingly difficult to find and keep skilled labor. Assembly and glazing in an environmentally controlled shop or factory setting is favorable to quality consistency and also makes more efficient use of labor,” he says. “The other phenomenon driving pre-glazing is time on the jobsite. The decision to glaze onsite or in the shop used to be up to the glazing contractor. As unitization and pre-glazing have become more prevalent, general contractors (GC) are fully realizing the benefits of
faster building dry-in.” He adds that general contractors don’t always leave the glazing decision up to the contract glazier and may restrict the elapsed time from start to finish of field fenestration installation.

What’s Next for Window Wall?

Over the past decade the multifamily construction market, which uses a
significant amount of window wall, has seen solid growth. That, however, could be changing. According to the Dodge Data & Analytics 2018 Outlook Report, the segment decreased 7 percent in 2017 and is projected to decline another 11 percent this year. The education segment, particularly K-12, which could offer opportunity for window
wall products, is expected to increase in 2018. (Take a look at USGlass magazine’s glass industry usage forecast on page 34 for a closer look at the segments poised for growth this year.)

Hiscock points out that window wall can be used in just about any building where the owner wants that aesthetic and an operable window.

“It could be used in a commercial building, but the owner doesn’t usually
want operable windows because they want to maintain the HVAC settings/conditions,” he adds.

To view the laid-in version of this article in our digital edition, CLICK HERE.

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