Volume 50, Issue 6 - June 2015

A Perfect Storm
Historic Retrofit for Hurricane Impact
Puts Windows to Task

by Nick St. Denis

Historic retrofits for hurricane and impact applications pose unique challenges, including compensation for weight and attention to matching existing sightlines while maintaining more stringent wind loads.

New construction in hurricane- and tornado-prone areas of the United States uses high-impact-rated glazing to meet stringent codes, and has for some time. Yet most existing buildings in those regions have had to upgrade their fenestration.

And in areas preserving their historic allure, the latter can be challenging.

An Impactful Study

A large-scale renovation to a historic school campus in Charleston, S.C., which re-opened as the Rivers Education Center in 2013, meant a complete gutting and overhaul of the building’s interior.

The exterior had some substantial work done as well. Though the inside has a new look, the outside kept its old one—while getting a whole lot tougher.

A key part of the unique 1930s building’s overhaul were the windows, which had to meet stringent code requirements for hurricane resistance and energy efficiency. St. Louis, Mo.-based Winco Windows was able to replicate the 9-foot-tall, historic single-hung windows—all 250 of them—while maintaining full code compliance.
Historical Challenge

Historic retrofits for hurricane and impact applications pose unique challenges. Winco is involved in a lot of these projects for buildings originally constructed anytime from 1900 to 1940. Kurtis Suellentrop, technical sales manager, says those buildings typically aren’t designed to withstand the bigger, stronger windows and systems required today.

“Because we were replacing older windows, they’re typically single-pane glass,” he says. “When using thicker glass, and laminated glass, you have to worry about compensation for weight. … And also, you’re trying to meet higher windload requirements while not affecting the aesthetics and sightlines of the overall project.”

One major challenge with a retrofit is figuring out how to marry the window with the existing wall condition, given any repair or restoration work to the wall that needs to be done.

The second big challenge, according to Suellentrop, is “to be able to match the existing sightlines and construction of the windows.”

“A lot of times in meeting these higher impact loads, you need to have a bigger ‘bite’ onto the glass to meet the glass edge requirements,” he says. “It’s hard to do that and still meet the sightlines of the older windows. … For example, the old way to do an old grid is to use a ‘T’ shape and put the glass on each side. But there’s no way to do that with inch-and-a-quarter-deep laminated glass and still meet those sightlines.”

From the Start

When doing historic retrofits, the Winco team prefers to get on site in the early stages of the design process and take measurements. Then, it’s ideal to remove one of the existing openings to see what conditions they’re working with, put in a mock-up and take that information back to the drawing board.

Winco has the ability to test in house, particularly for research and development purposes, but it can also test the products being designed for certain projects to ensure that they’ll pass a formal testing at an outside lab.

Lead times for the whole process can range from six months to two years depending on the project’s complexity.

School’s Out

Suellentrop says a lot of schools inquire about renovations, which is typically the case going into the summer months when they’re not being occupied, or at least not being occupied as often.

Because the historic retrofits take so much time—from initial measuring to designing to manufacturing and shipping—timing is key. In the case of this particular school, the project was completed almost two and a half years after Winco started the preliminary design.

Winco Windows was tasked with replicating 9-foot-tall historic single-hung windows for a 1930s school in Charleston, S.C. The new windows had to match the old ones aesthetically while being brought up to stringent hurricane impact and energy performance standards.

Seis-ing it Up

The 250 hurricane-rated historic replica windows weren’t the only part of the Rivers Education Center project that gave the building its newfound strength.

The project was considered a “seismic retrofit” and was reinforced to hold up in an earthquake—something the 1930 building wasn’t initially designed to do.

According to the general contractor M.B. Kahn Construction Co. Inc., the original building “was constructed of unreinforced multi-wythe exterior walls and unreinforced clay tile interior walls.”
While the replica windows and maintenance of the exterior helped the school keep its classic look with the help of the high-impact glazing, the building was made “seismically sound” with the installation of 627 micropiles that go 86 feet deep.

Why is seismic safety important in Charleston? Surprisingly, the coastal city has been hit by several earthquakes during the past 300 years, including one in 1886 that killed 60 people and caused an estimated $6 million in damages.

the author

Nick St. Denis is an assistant editor for USGlass magazine. He can be reached at nstdenis@glass.com.

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