What Are Seismic Roof Curbs?

Abbie Stancato At MicroMetl CorporationThe Merriam-Webster Dictionary defines Seismic as… “From subject to, or caused by an earthquake; also :  of or relating to an earth vibration caused by something else (as an explosion or the impact of a meteorite).” I’m thinking if your building just got struck by a meteorite you have bigger issues on your plate – I digress.

A structural engineer predetermines the seismic requirements of a building. This is dictated by the International Building Codes (IBC), and California Building Codes (CBC) based upon requirements set by the American Society of Civil Engineers (ASCE).

Seismic calculated curbs are available as reinforced metal curbs or vibration isolation curbs. However, don’t assume all vibration isolation curbs are seismically certified. Only a submittal stamped by a professional engineer (PE) is an acceptable form of certification. Additionally, seismic requirements are not fulfilled by just ordering a seismically stamped roof curb. Additional roof curb anchoring and methods of securing equipment to the curb are also a requirement, and must be adhered to for the certification to be valid. The additional requirements are detailed on each stamped submittal drawing.

What is Seismic Certification?

Seismic Certification is the result of several required actions, which begins with a stamped submittal provided by Manufacturers with assurance that after a Design Earthquake (DE) equipment shall maintain:

  • Structural Integrity
  • Functionality

Who Needs Seismic Certification?

California is the most obvious location in the US to require seismic certification. Although some structural engineers require a submittal stamped by a Professional Engineer from their specific state; many engineers will accept the California State stamp. However, a PE stamp can be obtained from all 50 states if required.

Earthquake Map At The MicroMetl Blog


As seen by this US Map provided by USGS, other locations throughout the US face the daily potential for seismic activity. Although the eastern half of the US does not face the same seismic factors as our neighbors to the west, many east coast homes and structures were never designed to withstand the seismic magnitudes that exist.



California Additional Seismic Needs At The MicroMetl Blog



Furthermore, California has sectioned off areas on the west coast as illustrated, and encompassed by the red border, which requires the most extreme certification standards.

Seismic rating requirements are not just limited to buildings in a seismic zone, many government buildings, and buildings designated as defense shelters also require seismically rated curbs.

Additional Benefits Of A Seismically Calculated Curb

An added bonus of a seismic calculated rated curb is the protection against high wind damage. All MicroMetl curbs are designed to the 2013 CBC, and 2012 IBC standards, and also meet the wind requirements for 155 MPH, three second gusts, Exposure C. This standard is less than the Miami-Dade wind standard, but is sufficient to fulfill other building requirements which may be called out by a structural engineer.

For those of you interested in the definition of “Exposure,” here it is as defined by the International Building Code…

  • Exposure A. This exposure category is no longer used on ASCE
  • Exposure B. Urban and suburban areas, wooded areas or other terrain with numerous closely spaced obstructions having the size of single-family dwellings or larger. Exposure B shall be assumed unless the site meets the definition of another type of exposure.
  • Exposure C. Open terrain with scattered obstructions, including surface undulations or other irregularities, having heights generally less than 30 feet (9144 mm) extending more than 1,500 feet (457.2) from the building site in any quadrant. This exposure shall also apply to any building located within Exposure B-type terrain where the building is directly adjacent to open areas of Exposure C-type terrain in any quadrant for a distance of more than 600 feet (182.9 m). This category includes flat open country, grasslands and shorelines in hurricane-prone regions.
  • Exposure D. Flat, unobstructed areas exposed to wind flowing over open water (excluding shorelines in hurricane-prone regions) for a distance of at least 1 mile (1.61 km). Shorelines in Exposure D include inland waterways, the Great Lakes and coastal areas of California, Oregon, Washington and Alaska. This exposure shall apply only to thos buildings and other structures exposed to the wind coming from over the water. Exposure D extends inland from the shoreline a distance of 1,500 feet (460 m) or 10 times the height of the building or structure, whichever is greater.

We serve customers with a wide range of seismic stamped roof curbs. Please contact MicroMetl for all your seismic curb requirements!

MicroMetl - Dedicated To Serving The HVAC Industry With Quality Products Since 1965
Dedicated To Serving The HVAC Industry With Quality Products Since 1965