By Taylor Larsen
The past few years have been an absolute boon for high-rise development, design and construction in Salt Lake City’s central business district. Those driving down State Street will soon be doing double-takes as the downtown skyline grows taller.
But how do these sites go from a tall idea into an even taller building? It comes from close coordination between A/E/C professionals in various trades—development, architecture and mechanical and geotechnical engineering, among others—to design and engineer these spaces to withstand everything Salt Lake City can throw at them, both economically and seismically.
Developer Viewpoint
Developers for Liberty Sky need to see past, present and future as they envision a neighborhood ecosystem in downtown Salt Lake City.
Going from, pardon the pun, the lofty ideations of a skyscraper to development has been a challenge for The Boyer Company and Cowboy Properties. Their joint venture is Liberty Sky with around 300,000 SF currently in construction in downtown Salt Lake City. They see the challenges to come in the changes that must happen before they break ground.
“Salt Lake City used to be a city that closed at 6 p.m.,” says Brent Pace, Project Manager with The Boyer Company. But with more people working and living downtown, things are changing. “There are so many things to do—Utah Jazz games, theatre, shows, concerts—it’s all right there.”
That building-up of amenities helps support a growing ecosystem of residents, restaurants and the various forms of entertainment that cities have to offer. Dan Lofgren, CEO of Cowboy Partners, says, “The most powerful symbol of ‘this is the place I want to live’ is seeing other people there. It’s a cycle—residents fill in a neighborhood and amenities emerge to meet their entertainment and dining needs, which attract more residents. Pretty soon, you have a thriving downtown neighborhood.”
Pace mentions two helpful catalysts in turning downtown SLC into a premier neighborhood, one of which is the Harmons downtown. “A sneaky piece of the neighborhood growth,” he calls the large-scale grocer currently operating next to 95 State, one of the skyscrapers in construction. It has helped provide a grocer in a food desert that makes walkability 100-percent feasible—a key issue in any downtown enhancement effort.
“We in the market don’t give enough credit to the LDS church as a landlord who maintains their assets impeccably well,” Pace says of the other catalyst he sees in making downtown SLC into a residential hotspot. “Temple Square, City Creek and their other assets have kept the downtown core energized.”
Lofgren adds onto Pace’s comments by pointing out another major catalyst in the healthy employment market Utah has enjoyed over the last decade. “Job growth in SLC and the Wasatch Front is as robust as anywhere in the country,” he says. “Demand for more luxury apartments is a reflection of the job growth that we see. That said, maintaining the balance between job growth and new units is something we are looking at every single day.”
He is ecstatic about the additional skyscrapers going up, again mentioning 95 State—the 24-story, class-A office building in construction down the street from Liberty Sky. “We couldn’t be more excited that there will be thousands of people who will be working in that building who we hope will want to live next door.”
It isn’t just developers and brokers who are winning with this, but city officials as well. “Salt Lake City recognizes the value of a high-rise residential building,” he says. Due to Liberty Sky’s 21 stories and 272 units of luxury residential in a market exploding with mid-rises, “this leased luxury high-rise is a brand new product type for downtown Salt Lake. We found ourselves working with the city in a very collaborative way to make Liberty Sky possible.”
Pace sees the Liberty Sky joint-venture between Boyer Company and Cowboy Properties as a no-brainer in today’s market—especially after the successes of these joint ventures in the past. “When we at Boyer determined that site wasn’t going to be an office, it was natural to look to and partner with Cowboy. This is too good of a site to not go vertical.”
With the right planning and the right space, developers are pushing to infill downtown with a product type that will change the skyline and push toward creating a true downtown neighborhood.
Liberty Sky
- Over 300,000 SF
- 272 units
- 21 stories
- Estimated completion date—January 2022
- Owner, Developer—The Boyer Company, Cowboy Partners
- Architect—Smallwood
- GC—Jacobsen Construction
Architectural Insight
High-rise architects are asked to provide high-density spaces that address environmental sustainability, amenity, and resiliency concerns.
In an era of urban renaissance, downtown developments are challenged to do more with less. In addition to providing high-density, amenity-rich housing, high-rise architects must minimize the carbon footprint of their projects while also designing for resiliency.
Emir Tursic, Principal with HKS Architects, leads the design of Kensington Tower, the 600,000 SF, 40-story residential building currently in design that will be located at the corner of State Street and 200 South.
Tursic says a key aspect on any high-rise design centers on efficiency. “These large-scale developments take a lot of resources,” he says. “When we make them as efficient as we can, we make them more sustainable, and that translates into construction efficiency and feasibility of the project as a whole.”
Architects like Tursic are thinking of sustainability in multiple ways. “Air quality is the threat that affects us [in Salt Lake City]—we do whatever we can to reduce the carbon footprint,” he says concerning the issue of sustainable energy and resource-use that comes from higher densities achieved by building vertically.
The other part of sustainability is resilience that foresees and mitigates present and future challenges—the sustainability of a well-designed, safe building that can last into the next century and beyond.
March’s earthquake reinforced this idea of sustainability, building upon a concept that HKS was already exploring with Kensington Tower, namely Performance-based Design. “We are doing site-specific seismic design instead of following prescriptive code requirements. We’re looking at the soil that the building will be on and designing to a maximum credible earthquake and customizing the structural design to meet that.”
The scale is also a test of architectural prowess, especially as Tursic and his team design what will become Utah’s tallest building. “Designing and articulating [high-rises] architecturally is a challenge. We want it to relate to the other buildings in the neighborhood.”
How will they do it? “The Kensington Tower modulates its massing to place the tallest portion of the structure away from other, shorter buildings, and steps down the mid-rise portion to relate to the scale of the adjacent mid-block development,” Tursic explains. The other trick with high-rise buildings is to articulate them in order to reduce their perceived scale and relate more to the human scale.
Height challenges of these building types are also a concern: “One foot taller on each floor and suddenly you’re building a whole other building on top of this one,” says Tursic. Finding the delicate balance in scaling correctly while maintaining efficiency is a key for any architect working on such tall buildings.
Other questions: how do you scale 40 floors and the hundreds of units going into them? “How do you design 377 residences—permanent homes for people—where each residence is as efficient and generous as possible?” asks Tursic.
The answers come in developing a variety of floor plates, or mixes of unit combinations that give each floor the variance that architects want. Tursic mentions the importance of creating an efficient vertical stack where the constraints imposed by mechanical systems are mitigated. “But providing different residence types that fit different unit mix and demographics is still important.”
It’s a tall task (I couldn’t resist) but one that the HKS team feels fully prepared for as they continue designing the tallest building in Utah. “Our market has matured,” Tursic concludes. “Salt Lake City is running out of space and the only way to go is up. […] We have this whole influx of people who want to stay downtown, and it’s exciting for the city to reach this new chapter in development.”
Kensington Tower
- 300,000 SF
- 377 units
- 39 total stories + roof terrace
- Estimated groundbreaking—Summer 2021
- Estimated completion—Fall 2024.
- Owner, Developer—Kensington Investment Company
- Architect—HKS Architects
- GC—Jacobsen Construction
Mechanical Adjustments
Engineers tasked with creating high-rise mechanical systems confront issues in both plumbing and HVAC work—leading to the creation of highly efficient buildings.
High-rise structures stand out in a number of areas—most notably in the mechanical realm. With many of these proposed structures over 20 stories taller than the three-story, or 75-foot, threshold defined by the International Building Code (IBC 2000), adjustments to standard, low-rise systems are needed for high-rise systems in order to adequately keep tenants and visitors safe.
In order to understand some of those adjustments, Kim Harris, P.E. and President Emeritus of VBFA explains some key differences in what are called “life safety issues” that come about while doing their mechanical engineering work in these high-rise structures. Water pressure, smoke mitigation, stair pressurization and fire sprinkler design are some of the issues that Harris has dealt with while designing the Salt Lake City Convention Center Hotel on 100 South and West Temple.
He says that water pressure is a critical issue for this building, currently still in construction. “The building heights change the way we design piping systems. It changes the design of the equipment, the valves, the piping and everything else to be rated for higher pressures,” Harris says. Although the equipment on the mechanical side doesn’t scale proportionally in cost, which is a relief in terms of overall expenses, it does require equipment rated to a higher number of pounds per square inch.
Harris and the VBFA team are under specific constraints with Salt Lake City’s 26-story Convention Center Hotel project. It took VBFA 18 months to design, which Harris says is because “it’s a complicated site. They had to tear down part of the Salt Palace, which led to a tight site with [the new construction] coming into an existing building.”
While site selection poses a unique test, Harris details how this and other high-rises in SLC present challenges to mechanical engineers tasked with heating and cooling a building.
“The building exterior envelope has a high percentage of glass,” Harris says of the hotel. The exterior glazing that goes to make such a beautiful glass façade on these high-rises is here to stay, as is the unique challenges that using those materials creates. “The south-facing, floor-to-ceiling glass presents a huge challenge.”
Harris says that code prevents a building from using over 30–40-percent glass on a prescriptive basis. But there is a catch. “You can get around that by showing savings in energy-usage in other areas by completing an energy model on the building,” he explains. “And our energy model showed that it beat the energy code overall. It’s still a highly-efficient building.” The malleable energy code allows a more perfect dance between the oft-competing ideas of aesthetics and practicality.
The problem-solving didn’t end there either. “The ground floor is probably even more challenging with its clear glass,” Harris says. The owner wanted full transparency so that there would be no reflection for those on the interior—that way, the ground floor can act as another sales pitch to passersby.
It’s an exciting time for Harris and other mechanical engineers to design these multi-purpose, high-rise buildings. They delight in overcoming the various challenges presented with plumbing, HVAC and energy use on 20-plus story towers.
Salt Lake Convention Center Hotel
- 685,000 SF (overall building area)
- 700 rooms
- 26 stories
- Estimated completion date—September 2022
- Owner, Developer—Salt Lake City CH LLC
- Architect—Portman Architects and FFKR Architects
- GC—Hensel Phelps Construction and Okland Construction
Geotechnical Grounding
How do you get a 20-story-plus tower to dance with downtown’s seismic concerns? Geotechnical engineers have the answer.
The geotechnical side of high-rise construction is concerned with making sure that these structures have the guidance needed to make them earthquake-resistant—something at the forefront of owners’ minds since the March earthquakes and aftershocks.
“We get involved very early on in the design process,” says Chris Garris, P.E., Division Manager and Principal Geotechnical Engineer for Consolidated Engineering Laboratories. “We’re out there sampling the soil, exploring soil conditions and developing conclusions and recommendations that are used for foundation design and other issues from the ground-down, typically before the building has been designed.”
It’s not just geotechnical foundation recommendations, but Garris and other geotechnical engineers are working together with structural engineers and providing them with seismic design parameters that the structural side will use in the building design.
For such tall towers, Garris references Performance-based Design (PBD) in a few more words. Geotechnical engineers analyze how the foundation interacts with the soil, particularly how it interacts with seismic and earthquake loads. As the building goes up in height, he explains that the foundation’s design is to resist downward compression loads, vertical uplift and lateral load reactions.
“A building is resting on these deep foundations,” Garris explains of the piles, the deep support mechanisms that often go down to depths of 100 or more feet to support the high-rises going up around the capital city.
“Depending on how a building rocks, the piles are either going to be put into a compressional load where the building is pushing down on them, or, if it’s kind of rocking the other direction, the foundations are actually going to be pulled on by the building. So there’s an uplift pulling those piles out of the ground,” Garris mentions, explaining the geotechnical concerns of these lofty structures. “In a PBD approach, the piles have to be designed carefully to define load versus deflection characteristics so that the soil-structure interaction may be appropriately modeled by the structural engineer.”
The piles he is referring to are known as auger caste or continual flight auger piles. Garris says that the piles are created by a two-foot diameter auger that drills down to the designed depth. As the auger retracts, workers pump in concrete grout. Construction teams then drop in steel reinforcement bars and cages into the wet concrete to reinforce the pile for its intended purpose.
According to Garris, this method has been used for high-rise projects in Salt Lake City’s downtown area more prominently since 2008 with the construction of City Creek. Currently, they are in use in 95 State, Salt Lake City Convention Center Hotel and Liberty Sky developments, and will be used in Kensington Tower.
“Downtown Salt Lake City has a very favorable, very dense gravel layer that’s about a hundred feet below the ground surface,” explains Garris of the reasons that these pile types have taken off in Salt Lake City. “You can drill these auger cast piles relatively easily down to that gravel and really give a very high capacity for both the axial uplift as well as the downward compression loads.”
“The auger cast systems have been very competitive to conventional driven piles due to their higher load carrying capacity per unit area. Auger cast piles are also less intrusive to the surrounding urban environment compared to more conventional driven steel piles that have traditionally been used in the downtown area,” he says of the skyscraper developments moving along. “And now we’ve got lots of great test data and it really shows the success of using this type of foundation system.”
He and other geotechnical engineers are making sure that Salt Lake City’s new skyline will be safe and reliable for tenants, residents and visitors alike for decades to come.
95 State at City Creek
- 498,000 SF
- 25 stories
- Estimated Completion—Fall 2021
- Owner, Developer—City Creek Reserve, Inc.
- Architect—Skidmore Owings & Merrill
- GC—Okland Construction
What’s Next
If the last 30 years have taught us anything about Salt Lake City high-rises, the growth in this area will be slow and steady. But if successful, these high-rises will establish Salt Lake’s central business district as a market where high-rises are a viable alternative to the other residential and commercial products already available.
“Market demand and the expectations of today’s tenants have changed,” Tursic of HKS concludes. “There is an urban renaissance happening. Tenants want downtown and they want the urban living, but they want the convenience of a single-family home. Salt Lake City is running out of space and the only way to go is up. It’s an exciting chapter in the city’s development.”
