Before the development and implementation of comprehensive
building codes, it was common practice for rooftop equipment to be
installed without being firmly attached to a building's structure.
The thinking was the weight of an HVAC rooftop unit would be
sufficient to keep a curb and the rooftop unit on top of a
building. However, recent research into the effects of natural
disasters has shown that to resist significant seismic and wind
loads, rooftop units must be firmly restrained from moving off
their curbs, and curbs must be attached to a building's structure.
This research is changing the way curbs are designed, built and
Many U.S. jurisdictions require a licensed engineer to certify
that curbs and restraints meet the requirements of applicable
building codes. The process by which curbs are now designed can be
summarized in three steps.
First, a roof curb designer must determine the governing
building code for a particular project. This information is
typically provided in the mechanical or structural sections of
project specifications. The designer should also be aware of any
project requirements that are more stringent than those listed in
the building code.
If the project specifications do not include an applicable
building code, the designer can determine it by contacting the
building department that has jurisdiction in the area where
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