Why Seismic Roof Curbs Exist
Seismic requirements stem directly from building codes and structural engineering standards. Design engineers determine the specific seismic criteria for each building, guided by:
- International Building Code (IBC)
- California Building Code (CBC)
- American Society of Civil Engineers (ASCE) Standards
Equipment mounted on a roof—especially heavier HVAC units—is vulnerable to shifting, tipping, or detaching during strong motion events. A seismic-rated curb solves this by providing a reinforced, engineered foundation designed to resist these forces.
What Qualifies as “Seismic Certification”?
A true seismic-rated curb is more than just heavy-duty metal:
It must meet two core requirements after a Design Earthquake (DE):
- Maintain Structural Integrity
- Remain Functional—meaning the HVAC unit still operates as intended
To achieve this, manufacturers provide:
- A professionally engineered (PE) stamped submittal
- Documentation verifying compliance with applicable ASCE, IBC, and CBC standards
- Required anchoring and attachment instructions
Important:
Ordering a curb with a PE stamp is not enough on its own. Installation must follow the stamped details exactly—attachment points, fastener types, spacing, and anchoring all matter. Deviating from the engineered plan invalidates the certification.
Where Are Seismic Curbs Required?
While California is the most seismic-active region and has the strictest regulations, it’s not the only area that uses seismic-rated curbs. Other regions require or recommend them due to:
- Proximi