Seismic restraint of HVAC equipment in Canada

When an earthquake strikes, the structure of a modern building is designed to stay standing. Its mechanical systems are a different story unless they are restrained. Unanchored rooftop units can slide off curbs, chillers can walk off their isolators, and swinging pipes can break at joints and flood a building. In past earthquakes worldwide, damage to nonstructural components has often been what kept buildings closed afterward.

The National Building Code of Canada (NBC) requires mechanical and electrical components to be designed to resist seismic forces in many parts of the country. This guide explains where those requirements come from, what they cover, and how seismic restraint is designed and verified on Canadian projects.

Seismic hazard in Canada

Seismic hazard varies widely across the country. The highest hazard is in southwestern British Columbia, including Vancouver and Victoria, along the coast to Haida Gwaii, and in parts of Yukon. Moderate hazard zones include the Ottawa and St. Lawrence valleys, including Montreal and Quebec City, and parts of the Charlevoix region. Much of the Prairies, including Edmonton and Calgary, has low hazard, though restraint may still be required for some buildings and components.

The NBC provides seismic hazard values for each location, derived from the Geological Survey of Canada's national seismic hazard model. The 2020 edition of the NBC adopted an updated hazard model, which changed design values in some locations. Always use the hazard values from the code edition in force in your province.

Code requirements

NBC Part 4

NBC Part 4, Subsection 4.1.8, covers earthquake design. It includes requirements for elements of structures, nonstructural components and equipment, often called operational and functional components (OFCs). The code provides a formula for the lateral design force on a component, which depends on:

• The site's spectral acceleration and site class (soil conditions).
• The building's importance category, with higher factors for post-disaster buildings such as hospitals, fire halls and emergency operations centres.
• A component factor and response modification factor from a code table, which differ for rigid and flexible components and for equipment on vibration isolators.
• The height of the component within the building, because accelerations increase toward the roof.

Isolated equipment receives higher design forces because spring isolators can amplify motion. Components in post-disaster buildings must remain functional after an earthquake, not just stay in place.

CSA S832

CSA S832, Seismic risk reduction of operational and functional components (OFCs) of buildings, provides guidance on identifying, assessing and mitigating seismic risk to building contents and systems. It is referenced by the NBC and is particularly useful for existing buildings and for planning restraint of equipment in critical facilities.

Other references

Designers commonly use the SMACNA Seismic Restraint Manual: Guidelines for Mechanical Systems for duct and pipe bracing, the ASHRAE Practical Guide to Seismic Restraint, and manufacturers' pre-engineered bracing systems. For healthcare facilities, CSA Z317.2 and provincial health authority standards add requirements for continuity of critical HVAC systems.

Provincial codes adopt the NBC requirements with local changes. British Columbia, with the highest hazard, has the most detailed practice and enforcement. Some municipalities and owners require a specialist seismic engineer to sign and seal restraint designs. Check requirements with the authority having jurisdiction.

What needs restraint

Typical HVAC items that require seismic restraint where the code applies include:

Codes and guides include exemptions for some small components, such as light piping or small ducts hung on short rods, but these exemptions have conditions. For example, exemptions may not apply where the component carries hazardous material, serves a post-disaster function, or could fall onto an exit route.

Design responsibilities

Seismic restraint is a coordinated effort:

1. The structural engineer designs the building structure and confirms that it can carry the forces from attached components.
2. The mechanical engineer identifies which systems need restraint, sets performance requirements, and specifies restraint in the contract documents.
3. A seismic restraint engineer, often retained by the contractor or the restraint supplier, designs the specific anchors, braces and attachments and provides sealed drawings and calculations.
4. The contractor installs restraints according to the approved design and coordinates brace locations with other trades.
5. A field reviewer, usually the seismic restraint engineer, inspects the installation and issues a letter of assurance where the authority having jurisdiction requires one.

Delegated design is common in Canadian practice. The specification should clearly state who is responsible for restraint design and what submittals are required. Our guide to mechanical permits and engineering seals explains how sealed delegated designs fit into the permit process.

Coordination with vibration isolation

Vibration isolation and seismic restraint pull in opposite directions. Isolators let equipment move to block vibration from the structure, while seismic restraint limits movement. Seismically rated spring isolators solve this with built-in limit stops that leave a small operating gap during normal operation and engage during an earthquake. The gap must be set correctly at installation, otherwise the stops touch in normal operation and short-circuit the isolation. See HVAC noise and vibration control for isolation selection.

Flexible connections are equally important. Piping that crosses a building seismic joint or connects to isolated equipment needs flexible connectors or loops that can take the expected relative movement without rupture.

Existing buildings

Older buildings, especially in British Columbia and Quebec, often contain unrestrained mechanical equipment installed before modern requirements. When equipment is replaced, the new installation is usually required to meet current code. Owners of critical facilities can use CSA S832 to prioritize upgrades, focusing on components whose failure would cause life-safety risks, flooding, loss of critical functions or costly downtime.

Frequently asked questions

Do buildings in Calgary or Edmonton need seismic restraint?

Hazard values are low on the Prairies, and many components fall below the thresholds that trigger restraint design. However, requirements depend on importance category, site class and component type, so post-disaster buildings and some equipment may still need restraint. The structural engineer of record should confirm.

Can vibration isolators double as seismic restraint?

Only if they are seismically rated and certified for the design forces. Standard open springs provide no lateral restraint and can make seismic movement worse.

Who inspects seismic restraint?

Typically the engineer who designed the restraints performs field reviews and issues a letter of assurance. Building officials may also review it as part of the permit, depending on the jurisdiction.

Key takeaways

• NBC Subsection 4.1.8 requires seismic design of mechanical components in many Canadian locations, with forces based on hazard, importance and component type.
• Seismic hazard is highest in coastal British Columbia and moderate in the Ottawa and St. Lawrence valleys.
• Equipment on isolators needs seismically rated isolators or snubbers with correctly set gaps.
• Responsibility for restraint design is often delegated, so specifications must state who designs, seals and reviews it.
• When replacing equipment in older buildings, plan to bring restraint up to current code, a point worth raising early in HVAC design.