Salt Lake Temple base isolation: a $2B seismic retrofit to protect the world’s largest Mormon temple

The B1M takes you inside Salt Lake City’s iconic Salt Lake Temple, the largest Mormon temple in the world, and explains a transformative $2 billion upgrade. The video outlines how base isolation will let the granite landmark move independently during earthquakes, protecting its stonework and interior. It walks through the installation of 98 base isolators, a new concrete foundation, and more than 423 kilometres of post-tensioned cables, all while reinforcing walls and architectural features. We also get a primer on the temple’s history, from Gothic and Romanesque design to Brigham Young’s Plat of Zion urban plan that anchored Salt Lake City’s grid. The project aims to complete in 2026 with doors reopening in 2027, signaling resilience for a historic symbol.

Overview

The Salt Lake Temple, completed more than a century and a half ago, remains a defining symbol of Salt Lake City and of The Church of Jesus Christ of Latter-day Saints. This video explores the ambitious retrofit described as a $2 billion operation to render the world’s largest Mormon temple seismically resilient through base isolation. The approach aims to minimize damage to the temple’s ornate masonry and historic interior while maintaining its ceremonial functions and architectural integrity.

Why the Temple Needs Protection

Located in the Wasatch Valley, Salt Lake City sits near the Wasatch Fault, where geologists estimate a magnitude 7 earthquake could strike on a millennial scale. The video cites a 57% probability of at least one earthquake of magnitude 6 or greater in the next 50 years, underscoring the urgency of strengthening historic structures that were not designed for modern seismic events. The Christchurch earthquake of 2011 is referenced as a case study in how heritage buildings can suffer severe damage and how retrofitting can enable safer preservation rather than demolition.

Base Isolation: How It Works

To reduce earthquake forces, the temple is being decoupled from ground motion through base isolation. The system allows up to 1.5 metres of horizontal movement in any direction, helping protect ornate stonework, interior spaces, and occupant safety. Engineers excavated to create a new lower level for isolators. They employed underpinning techniques including micro piles, secant piles, tie-back anchors, tensioned tie rods, hand-constructed underpinning piers, and consolidation grouting to stabilize the existing structure during modification.

Engineering Details

A new concrete foundation with transfer beams and girders surrounds the temple to distribute loads. Post-tensioned cables—more than 423 kilometres in total—tie the temple to the new foundation, guiding load transfer as the structure moves. The retrofit includes 98 base isolators, each weighing about 8000 kilograms, acting as bearings between the temple and its foundation. After isolators are installed, soil beneath the foundation will be removed to allow the structure to float on the isolators during seismic events. The vertical stiffness supports vertical loads, while horizontal flexibility accommodates ground motion, a key principle in base isolation design.

Construction Challenges and Modern Upgrades

Retrofitting a 19th century stone building is inherently delicate. The project timeline has extended beyond the initial target of 2025 into 2026 as crews reinforce spires and architectural elements and expand spaces for ritual baptisms and instruction rooms. A North addition with a ceiling wing will house additional wedding spaces. While the temple remains functional in part, the project’s scope extends beyond stabilization to upgrade the building’s seismic resilience and capacity for contemporary use, while preserving its historic character.

Historical Context and Urban Planning

The temple is not only a religious edifice but also a keystone of Salt Lake City’s urban plan. Brigham Young’s Plat of Zion laid out a highly organized grid with an 11-acre temple block at the center. The grid featured unusually wide streets and large block sizes that created a hybrid urban-rural model, aiding early self-sufficiency, fire protection, and future adaptability for cars. The temple’s Gothic and Romanesque design, with iconography such as stars, suns, the Big Dipper, and the Moroni statue, served as a storytelling vehicle for faith and community. The council and community later faced pressure to preserve historic buildings as land values rose and development pressure increased, amplifying the significance of a project that can act as a precedent for heritage preservation under threat.

Implications and Outlook

The renovation aims to demonstrate that even iconic historic structures can be reinforced to withstand seismic hazards without losing their essence. If successful, it could inspire broader preservation efforts within seismically active regions and signal a blueprint for balancing heritage with modernization. The doors are scheduled to reopen in 2027, marking a milestone in the intersection of architecture, urban planning, and earthquake engineering.