Protecting the Salt Lake Temple for Future Generations

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Amajor seismic base isolation and renovation project for the iconic Salt Lake Temple of The Church of Jesus Christ of Latter-day Saints (the Church) in Salt Lake City, Utah, will be completed at the end of 2026. Constructed over a 40-year period beginning in 1853 when Salt Lake City was still a small pioneer outpost, the temple’s stacked granite block construction contributes to both its historic significance and its seismic vulnerability. Because of the temple’s iconic importance, the Church undertook a years-long process of engineering and architectural studies to determine how best to preserve it for future generations.

Few historic preservation projects have attempted to seismically isolate a stone masonry structure of this scale while preserving its architectural and historic character. This challenging project required development of new analytical approaches, specialized construction techniques, and innovative load-transfer systems to achieve the owner’s long-term performance objectives. Adding to the challenges were unforeseen existing conditions, evolving project requirements, and the need to develop entirely new construction means and methods capable of achieving the project’s engineering objectives.

Two future articles will discuss the project’s engineering and construction approaches in more detail.

The history of the construction of the Salt Lake Temple illustrates dedication, vision, faith, starts, stops, ingenuity, change orders, and changing technology.

In 1846, the Latter-day Saints were driven from their homes in Nauvoo, Illinois, beginning their westward migration that would eventually bring them to the Salt Lake Valley in 1847. A few days after Church leader Brigham Young arrived with the Pioneer Saints in the barren Salt Lake Valley desert on July 24, 1847, he struck his cane down on a specific plot of ground and declared, “Here will be the Temple of our God.” This declaration demonstrated the importance of building the temple to the people whose current objective was to plant crops, dig irrigation ditches, and provide shelter to survive the upcoming winter. The construction of a temple was a daunting task, considering that supplies would need to be transported via wagon trains.

The Temple has become an iconic symbol of the Church and an example of uniquely American architecture, but it was not designed by a trained and experienced architect. Truman O. Angell, a carpenter by trade, was appointed by Young in 1848 as the church architect. His design for the temple was heavily influenced by the church leader who saw the temple in a vision. Young insisted the temple have three towers or spires on the east end and three on the west end. The towers on the east were to be a little higher than those on the west. The center towers were also to be higher than the adjacent spires. Angell used some architectural pattern books to work out the design details, such as Edward Shaw’s Rural Architecture (1843). In addition to designing the exterior stone of the temple, Angell also developed stone drawings for every stone above the foundation. Each stone was given a unique identification using numbers and letters (Fig. 1).

Three descriptive bills and diagrams were used—one for the architect’s office, one for the quarry, and one for setting the stone.

The groundbreaking to begin the excavation for the temple occurred on February 14, 1853 (Fig. 2). Four cornerstones were laid on April 6, 1853—a significant accomplishment given that the excavation was 16 feet below ground level on the east side.

A temple of the scale envisioned by Young needed a substantial foundation. Fortunately, the soil below the temple is well-consolidated sand and gravel deposited from the nearby City Creek Canyon, rather than the clay soils so prevalent in the Salt Lake City area. The base width of the tiered sandstone foundation varies from 16 feet (4.9 meters) at the north and south walls and up to 40 feet (12.2 meters) at the east and west tower complexes. The sandstone for the foundations came from City Creek Canyon, 4 ½ miles (7.2 kilometers) east of the temple.

It took more than 10 years to finish the construction of the sandstone foundations. The work was interrupted by winters, farming, and the need to completely bury the foundation work in 1858 over fears of an approaching U.S. Army in the Utah War. One of the most time-consuming efforts, however, was the rework that needed to be done to provide a more durable and level base to support the cut granite stones for the walls that would extend above grade level. Several layers of stone needed to be removed, and new “flagging” stones cut to provide a solid level support. Construction of the sandstone foundations continued until 1864, when granite basement wall stones finally began to be placed on top of the flagging stones.

The large granite (quartz monzonite) stones for the walls came from Little Cottonwood Canyon about 20 miles (32 km) southeast of the temple. It was a four-day round trip bringing the heavy stone blocks to the temple site on oxen-pulled wagons. By 1873, 20 years after construction began, the granite blocks were only about 3 feet (1 meter) above the surrounding ground (Fig. 3). Once the railroad arrived in Utah in 1869, a rail line was extended to the quarry in Little Cottonwood Canyon in 1872, which greatly accelerated the construction of the temple walls.

The original drawings showed two levels of large open floors supported on wooden floor trusses with two rows of interior columns. The center portions were tall two-story spaces with mezzanine floors on either side. The stone drawings showed stone notches to support the trusses and the mezzanine floors, and stone walls were constructed with these notches. Early drawings of the temple showed six flat towers, and later versions showed wooden towers. The 40 years of construction afforded plenty of opportunities for change.

Examples of change include events in 1887 and 1888 that had significant implications for the temple. At this time, after 34 years of construction, the north and south walls had reached their full height, and the towers matched the height of the walls. The interior floors were still not installed. Church President John Taylor passed away in July 1887, and Church Architect Truman Angell passed away in October 1887. Truman’s son, Truman Angell, Jr. had been a strong proponent of switching to stone towers, but this was resisted by Angell, Sr and President Taylor. Following their deaths, the idea was again presented to the new Church leadership, and the decision was made to switch to stone towers. In 1888, Don Carlos Young assumed Angell’s responsibilities on the temple. He was educated as a civil engineer, having received a degree from Rensselaer Polytechnic Institute in Troy, New York.

Young now oversaw the completion of the exterior stone towers and interior of the temple (Fig. 5). Under Young’s leadership, the interior framing changed from wood trusses to using steel girders to support the floor system. This change allowed for longer floor spans, thus requiring the use of only one interior granite bearing wall. This change had some implications for the stone walls because block-outs were already carved into the stone. These voids had to be filled in, and new block-outs created to support the steel girders. In addition, the originally envisioned lower-level open floor was now changed to smaller rooms, some with various floor elevations. Under Young’s direction, the originally planned wood roof trusses were changed to steel trusses.

The decision to switch to stone towers had significant structural implications. The stone towers added significant mass, resulting in higher bearing pressure on the stone foundations that were laid about 35 years previously (Fig. 6). During the current renovation project, it was noted that there was uneven settlement of the masonry with the original mortar joints dipping down at the towers. The greater settlement at the tower is correlated to the increased tower mass and increased soil bearing pressure. The stone towers also added significant complexity for the current base isolation project. Part 3 of this article series will focus on the Temple retrofit including the base isolation system, the load transfer system to get the loads onto the isolators, a vertical post-tensioning system throughout the walls and towers of the Temple, an innovative post-tensioned steel framing system inside the spires, and the installation of a new roof diaphragm with connections into all the towers.

The temple was completed and dedicated in 1893—40 years after construction began.
Beginning in 1962, the temple underwent a major renovation, which included replacement of mechanical systems, plumbing, and fire sprinkler lines. New above ground and below ground additions were added to the north of the temple, including a new structure (called the Sealing Addition), which was constructed against the north face of the temple. The current project removed the four structures noted in Figure 7, and a new Sealing Addition was constructed on the base isolation system of the temple.

Salt Lake City sits adjacent to the Wasatch fault, one of the most active normal fault systems in the United States and the principal seismic hazard along Utah’s Wasatch Front. It extends 220 miles (350 kilometers) from southern Idaho to central Utah and is divided into 10 segments. The temple is within 11/4 miles (2 kilometers) of the Salt Lake City segment, capable of an M7.2 earthquake. Paleoseismic investigations indicate an average recurrence interval of approximately 1,300 years for major earthquakes on the Salt Lake City Segment, and the elapsed time since the most recent event exceeds that average interval. This information weighed heavily on setting the design criteria for the temple.

Starting in the late 1990s and early 2000s, the Church began to assess the seismic vulnerability of its older temples and other buildings. In 2005, the Church commissioned a seismic evaluation by Degenkolb Engineers and a structural building assessment study by ARW Engineers. These studies identified that significant stone sliding could occur resulting in potential collapse. The studies developed two possible retrofit approaches. The first approach was to provide life safety to the occupants, but it was very invasive and required significant interior work that would destroy the historical finishes inside the temple. This approach would not protect the building from significant damage following the shaking from a strong earthquake. The second approach recommended using base isolation. This approach would significantly reduce the amount of required strengthening and would protect both the occupants and the historic structure from future earthquakes. The seismic evaluation was peer reviewed by Forell Elsesser Engineers.

In the early 2010s, many of the mechanical and electrical systems in the temple and north addition began to need repair and improvements. As the scope of this work evolved, questions about combining this work with seismic improvements began to arise.

Starting in 2014, the Church authorized additional base isolation feasibility studies by Forell Elsesser engineers. Final approval to begin construction documents was provided in 2018. The life of the temple is expected to be measured in centuries. Given this exceptionally long lifespan, the seismic design considered the severe shaking associated with a major rupture of the Wasatch fault rather than relying solely on the significantly lower, code-prescribed MCER ground motion. The code probabilistic approach does not fully represent the shaking that could occur if such a rupture were to happen near the temple. The project therefore adopted a design ground motion based on the 84th-percentile shaking from a magnitude 7.2 earthquake on the Wasatch fault. Even under this severe level of shaking, which includes unusually intense vertical acceleration input, the temple is expected to experience only minimal damage, helping preserve the historic fabric of the edifice. These demanding performance objectives drove many of the project’s engineering decisions.

Although base isolation was selected early as the preferred seismic retrofit strategy, subsequent computer modeling demonstrated that isolation alone would not achieve the desired performance objectives. Detailed dynamic analysis unexpectedly revealed that vertical excitation could induce significant horizontal oscillations and sliding demands within the stone tower system. The tower and wall systems needed to be strengthened to meet the performance objectives. A new structural diaphragm was also needed at the roof level to ensure that the towers, walls, and roof were well anchored together. For more detail, look for Part 3 of this series.

A significant piece of the project was the base isolation of the historic temple. The temple now rests on 98 Triple Pendulum isolators from Earthquake Protection Systems, but the process of creating and moving the 190-million-pound (86 M kg) temple onto the isolators and the new footings, adjacent to both sides of the temple foundation, was long and complicated. Three aspects of the load transfer system resonated with the Church during the planning process. The first was that the temple would permanently rest on its original stone foundation. The second was that the native soil the stones were directly set upon would remain until after the load transfer process. The third was that the temple would never “know” that its foundation had been re-supported during load transfer. The soil beneath the temple’s new load transfer system was only excavated after the load had been moved onto new footings flanking the existing walls and towers. For more detail, look for Part 3 of this series.

In addition to addressing the seismic structural concerns, the project included the replacement of aging mechanical, electrical, plumbing, and fire sprinkler systems. Improvements to accessibility and comprehensive enhancements to the temple and surrounding ground were also included.

This seven-year construction project encompassed two city blocks with a primary focus on the historic temple. The project included the renovation and seismic upgrade of the Salt Lake Temple and added three below grade levels and two entry pavilions to the north of the temple. The new pavilions provide temple access and additional temple functions and were not base isolated. Two new visitor center buildings were added to the south. The project also included two blocks of new landscape, street improvements, and renovations to other buildings on the blocks (Fig. 8). The excavation for the three below grade levels adjacent to the historic temple required excavating 45 feet (13.7 meters) below the existing historic foundations. To maintain the capacity of the very high bearing pressure on the existing foundation and new footings, extensive shoring was required. Part 2 of this article series will focus on the geotechnical studies and field monitoring of the site as well as the extensive scope of shoring systems required to construct the adjacent buildings while also protecting the temple against settlements and movements.

Figure 9 provides a simple overview of the load transfer system. Some of the steps needed to construct the system are listed here. For a discussion of the complexities and unique solutions that were considered to accomplish these steps, look for Part 3 of this series.

The Salt Lake Temple project demonstrates how modern seismic engineering can be applied to preserve and strengthen historically significant structures while meeting ambitious performance objectives. Achieving these goals required close collaboration among engineers, architects, contractors, specialty subcontractors, and the owner. Two future articles will examine the engineering solutions developed to meet these challenges.

The temple now stands prepared to withstand the major earthquakes expected along the Wasatch fault while preserving its historic character for future generations.

The Salt Lake Temple will be open for public tours from April 5, 2027, to October 1, 2027. For more information about the celebration and to view seven years of project updates, visit www.templesquare.org. ■

This material is neither made, provided, approved, nor endorsed by Intellectual Reserve, Inc. or The Church of Jesus Christ of Latter-day Saints. Any content or opinions expressed, implied, or included in or with the material are solely those of the authors and not those of Intellectual Reserve, Inc. or The Church of Jesus Christ of Latter-day Saints.

Mason Walters, SE, NAE is the Project Principal for Forell Elsesser Engineers.

Rene Vignos, SE, is the Project Manager for Forell Elsesser Engineers.

Brent Maxfield, SE, is a structural engineer in the Special Projects Department of The Church of Jesus Christ of Latter-day Saints but is not speaking for the Church in an official capacity.