In 2009, two Texans surveyed the same historic site in Houston’s Fourth Ward and made very different observations. One, a Houston city official, saw the remnants of a church founded by freed slaves in the 1890s and a priceless cultural landmark. Another—a structural engineer—also appreciated the building’s significance while noting another issue: the church’s north wall, 55 feet tall and cracked, posed an imminent safety threat to passersby.
“I immediately called the city and said, ‘We can’t do anything until we make it safe,” recalls the engineer, Jacob Bice, senior principal at Walter P Moore.
Those contrasting impressions underscore the challenges that engineers often face on historic preservation projects. The goals on such projects can include preserving as much of a historic structure as possible—especially the facade and other significant aesthetics—while also modernizing the building and enhancing its structural integrity. That often means massive design changes to the building’s core.
However, that sort of painstaking preservation isn’t right for every old building, or even every historic building. Cost is a factor, as are the wishes of building owners and other stakeholders.
As Bice and other local stakeholders surveyed the Houston site, they worked through a calculus familiar to historic preservation projects.
“You have to decide: Is this the piece of the map that matters most to your community? Is this the one that you want to last in perpetuity?” says Bice. “It’s always faster, cheaper, and easier to go back in and construct new structures. But with buildings that inform the cornerstones of a community, we have a responsibility to be good stewards. There’s an investment, but you’re investing with the understanding that these buildings are the places that really define where we are.”
The Houston project, which was completed in 2013, resulted first in the stabilization of the damaged wall that Bice had identified, and later in the creation of Bethel Church Park—an award-winning project that preserved several external walls from the original historic building and integrated them into an openair park with a steel frame whose shape echoes the vault of the original church’s roof.
The park looks substantially different from the original church, but the team took care to preserve key historic components where possible. For example, when demolition teams encountered an “X” etched into a concrete frame, they called in archaeologists, who confirmed that the X was a hallmark of buildings constructed by freed slaves. The team then adjusted its plans so that it could preserve the X and the surrounding frame.
“Those beams are not in the greatest shape, but they’re there purely because it’s some of the last symbology from the original congregation that’s still visible,” Bice says.
The initial analysis of whether or how to proceed with renovations isn’t always easy—and that’s just the beginning of the challenges posed by preservation projects. For starters, for many older buildings, the original plans, details, and analyses are not available, as they would be for more recent construction projects. “It is critically important to understand the beast before you can properly intervene,” says Gary Mancini, managing principal and renewal practice leader at Thornton Tomasetti in New York City.
A smart first step in the effort to gain that insight is to focus on discerning “what was in the mind of the people who designed and built it, and how they intended for the structure to work,” Mancini says. In other words, engineers need to determine how archaic or empirical approaches to engineering informed the original design and construction decisions.
For example, when Thornton Tomasetti engineers worked to stabilize and modernize Wrigley Field, an iconic, century-old Chicago baseball stadium, the firm recognized that “Back then, structural engineering was in its infancy, and people were still perfecting their approaches to managing vertical and lateral loads,” says Steve Hofmeister, managing principal and structural engineering practice co-leader at Thornton Tomasetti and a leader of the Wrigley Field project completed in 2019.
As a result, Wrigley Field’s original partition walls tightly abutted the stadium’s columns, resisting most of the lateral loads on the ballpark. The program requirements of the restoration project mandated that the team shift the location of the partition walls so that they weren’t connected as directly with the columns. Therefore, the team included a lateral system to resist modern code-required lateral forces.
The design of the original structure didn’t age well either, having taken on lots of structural damage when water built up between the concrete and steel elements. When Hofmeister’s team began the restoration project, some of the columns had decayed so much that they were essentially useless, underscoring the need for new, modern supports.
Which leads to Mancini’s second point: Just as it’s crucial to understand how the building was supposed to function, it’s equally important to understand how it’s actually functioning. “Sometimes the load paths that a building experiences have been altered over the years because of weathering and deterioration of the building’s systems and components,” he says.
Mancini once worked on a hotel restoration project in Midtown Manhattan, where several of the steel spandrel beams were found to have decayed dramatically—“to a point where portions of the beams were literally reduced to mere rust stains on the masonry”—but the building continued to function by redistributing loads to the masonry below. “Structures can be very forgiving when changes occur slowly over time. As an engineer, you really need to understand the existing material properties and make sure that your interventions respect how the building has actually behaved over the years,” Mancini says. “Otherwise, you can invite problems in the future.”
Thanks to advancements in technology, firms can now perform detailed load testing, analysis of materials, and building performance using modern instrumentation and digital modeling, such as finite element modeling and digital twinning, in ways that weren’t possible just a few years ago.
Still, materials remain one of the more daunting aspects of historic preservation projects because the buildings involved often include materials that are unfamiliar, degraded, or both. Most modern engineers aren’t trained extensively in working with terra cotta and limestone, for example, in the way they once may have been. Success in historical preservation means getting up to speed on the quirks and characteristics of those older materials—and then getting creative in their application.
“There’s an investment, but you’re investing with the understanding that these buildings are the places that really define where we are.”
JACOB BICE
SENIOR PRINCIPAL
WALTER P MOORE
“It is critically important to understand the beast before you can properly intervene.”
GARY MANCINIMANAGING PRINCIPAL ANDRENEWAL PRACTICE LEADERTHORNTON TOMASETTI
At the Park Avenue Armory in New York City, engineering firm Silman worked to reinforce the large Drill Hall with wrought iron trusses, as well as the adjacent Head House that employed wooden joists and flooring. When developing its strategy, the Silman team leaned on the expertise of colleagues who specialize in wood-framed residential construction—not the expected frame of reference for historical preservation of a Manhattan landmark, but exactly what the job called for.
“All the details and strategies that you lean on in more conventional projects—tricks about reframing and notching and re-supporting—those all become part of our toolkit or painter’s palette for when we do an intervention in a historic building,” says Eytan Solomon, a senior associate at Silman who helped lead the Park Avenue Armory project.
Similarly, Solomon’s team analyzed the wrought iron trusses in the armory’s Drill Hall and determined that while the trusses were sound, they would benefit from additional support, given the property owner’s plans to use the building as a performing arts venue. The team searched for ways to add support without changing the look of the historic Drill Hall. They came up with a novel solution: welding steel plate reinforcements onto the wrought iron.
The design, Solomon says, was so sensitive that “You can’t even tell, unless you’re right up close to it and touching it—and maybe not even then, because down to the welding details and the grinding and painting, we worked with the architects to make sure that the [steel elements] were as minimally intrusive as possible.”
Of course, it’s one thing to devise a smart intervention, and another to implement it—especially in a historic context where every surface is worthy of preservation. That was Solomon’s next challenge, and one that’s familiar to most engineers working on historic preservation projects.
“All the details and strategies that you lean on in more conventional projects—tricks about reframing and notching and re-supporting— those all become part of our toolkit or painter’s palette for when we do an intervention in a historic building.”
EYTAN SOLOMONSENIOR ASSOCIATESILMAN
“When a facility is so historic, such as either Wrigley Field or Climate Pledge, it’s just socially unacceptable to tear it down.”
STEVE HOFMEISTER
MANAGING PRINCIPAL AND STRUCTURAL
ENGINEERING PRACTICE CO-LEADER
THORNTON TOMASETTI
Access to at-risk spaces is often a huge issue in historic preservation projects. In order to get close enough to intervene in support of one element, teams frequently must remove or alter another element—and those building features are often themselves historic and worthy of preservation.
That means creativity and collaboration are crucial. At the Park Avenue Armory, for example, Solomon’s team coordinated timing with a concurrent phase of the project that involved a temporary removal of the armory’s roof, and that’s when they moved in to weld the steel supports onto the old iron trusses.
While typical reinforcement projects involve working behind existing finishes, “A lot of times, you don’t have that perfect access when you’re trying to preserve the room,” says Solomon. “So you pull out all the tricks—like, if the ceiling is to be preserved, do you have access from the floor above so you can get in and do the work that way? Or maybe you’re selectively and carefully removing finishes and putting them back.”
Removing and replacing certain elements is similar to what Thornton Tomasetti’s Hofmeister did on another recent arena preservation project to restore Climate Pledge Arena in Seattle, except at scale. That stadium was constructed for the 1962 World’s Fair and was too cramped to accommodate modern professional sports events. So the firm detached and suspended the stadium’s roof—the building’s most iconic feature—for two years while digging more than 60 feet into the ground so that it could construct a new arena.
Raising the roof wasn’t cheap or easy, but it’s what made the project possible. And on some prominent historic preservation projects, that’s the primary imperative. “When a facility is so historic, such as either Wrigley Field or Climate Pledge, it’s just socially unacceptable to tear it down,” Hofmeister says. “Building a new ballpark in Chicago might make financial sense from a construction cost point of view, but you can’t tear down Wrigley Field. And that often means the economic considerations are different.”
For the engineers working on historic preservation projects, the work represents both a technical challenge and also a chance to make a unique and meaningful contribution.
The work of a modern engineering team often isn’t especially visible or celebrated; visitors are more likely to appreciate the enduring historical elements. But that’s the point.
Says Silman’s Solomon: “I’ve accepted that a lot of our work is not seen by the end users of the building. But it’s fun to have the quiet satisfaction that you contributed to something that was difficult to do and has had a really great impact on people.”
Steve Hendershot has contributed to Crain’s Chicago Business, Chicago magazine, and Chicago’s NPR affiliate, WBEZ, and is host of the Project Management Institute’s Projectified podcast. He lives in Chicago.
Cost is among the greatest impediments to historic preservation projects—and not only because such projects are often more expensive than building from scratch. The other main consideration is unpredictability because the unique elements at play in preservation projects generally mean that costs are difficult to anticipate with precision.
“Anybody can estimate the cost of a new medical office building or a new hospital because there are many comparable [projects] that you can draw data from. There is nothing that you can draw data from on what it’s going to cost to jack up a 45-million-pound roof, cut off the footings, extend them 60-some feet down, and build a new arena,” says Steve Hofmeister, managing principal and structural engineering practice co-leader at Thornton Tomasetti, referring to his firm’s project to rebuild Climate Pledge Arena in Seattle.
Of course, smart engineering can help building owners greatly reduce construction costs and keep projects on schedule. On another Thornton Tomasetti project—230 Park Avenue (also known as the Helmsley Building), the grand Beaux Arts-style commercial highrise near Manhattan’s Grand Central Terminal—the owner was unsatisfied with another consultant’s proposed repair solution because it required removing and replacing the enormous terra cotta brackets that support the three story-high decorative columns near the top of the building’s ornate facade. After performing an advanced analysis that included a finite-element model of the load path and stresses, the Thornton Tomasetti team proposed a customized cost-effective solution: to reinforce and stabilize the existing brackets in place and install an impressed current cathodic protection system to arrest internal steel corrosion. The approach dramatically decreased overall costs to one-quarter of the earlier proposal and allowed the original historic materials to remain in place, helping to ensure that the project moved forward.