guidelines serve as a supplement & do not supersede the specific
installation instructions supplied with the unit curb.
Roof curbs should be supplied by the unit manufacturer to the general
contractor or building manufacturer & installed by an experienced erector.
The erector should follow the installation instructions for assembling
& installing units on curbs. Full perimeter or partial perimeter roof curbs
should be selected based on the application.
Roof curbs should match the exact footprint of each unit being
provided. Review curb drawings & specification for information on unit
dimensions, weight, cross braces, component details, supply & return
opening layout dimensions.
Curb should be structurally capable of supporting intense loads &
designed such that drains & power lines do not penetrate roof flashing. Roof
flashing should not be directly attached to a rooftop unit.
The curb should be furnished with a wood nailer to permit mechanical
attachment of the flashing material.
Use of improperly designed internal & external isolation springs
can cause vibration.
The recommended nominal curb height is at least 14 inches. The
curb material should be galvanized steel & may vary from 18 to 14 gage
based on the unit load & quantity of cross bracing provided.
Elevated roof curbs or dunnage steel should be used to support the
unit to raise it to specific heights. Unit access should be considered while
selecting roof curbs. Review selection meets local codes & regulations.
The unit shall include an integral design base rail with lifting
points marked & connections for condensate drainage. A recessed curb
mounting surface provides a continuous surface for field application of curb
gasketing to create a weather tight seal between the curb & unit.
Connect ductwork to the curb prior to setting the units. Unit &
curb orientation is critical during install. Review air flow marking on the
curb or unit detail drawings prior to install.
Ensure roof curb is square & level prior to setting equipment. Installer
should ensure watertight connection between the unit & the curb by applying
a sealing material. Sealing material prevents moisture & air leakage into
& out of the duct system.
Install seismic isolation curb in seismic zones, to support unit
vibration & to offer seismic/wind restraint. (Reference: International
Building Code 2003( IBC – 2003 section 1621) & American Society of Civil Engineers
(ASCE 7-02 section 9))
Use of flexible collars should be done when connecting duct work to
prevent noise transmission & vibration into the building.