All rooftop air-handling units shall be supported by vibration isolation
curbs as manufactured by Kinetics Noise Control. The vibration isolation
curbs shall be complete assemblies designed to resiliently support equipment
at the specified elevation and shall constitute a fully enclosed air- and
The isolation curb shall consist of an upper support rail with supply and
return duct supports on which the equipment and duct openings rest and a
lower support curb which is attached to the roof structure, separated by
free-standing, unhoused, laterally stable steel springs.
The upper support rail shall provide continuous structural support for
the rooftop equipment and shall be designed to provide isolation against
casingradiated vibration in the rooftop equipment housing and structure borne
vibration from rotating and mechanical equipment in the rooftop package.
The upper support rail shall consist of a structural channel with sufficient
elevation above the spring to preclude interference with the rooftop equipment
and permit access to inspect the isolation system after placement of the
rooftop equipment. Support of the RTU by weather seal attachment bolt heads
is not permitted.
The lower support curb shall be a formed channel fabricated of heavy gauge
galvanized steel with a continuous 1-1/2 inch x 1-1/2 inch (38 mm x 38 mm)
nominal wood nailer attached to the isolation support pedestals. The isolation
support pedestal, which includes the seismic and wind load restraints, shall
be bolted or welded to the building support steel to suitably transfer seismic
and wind load forces to the building structure. The lower support curb shall
have a minimum elevation of 14 inches (356 mm) from the top of the wood
nailer to the base of the curb.
Spring components shall be (1 inch/25 mm) (2 inch/51 mm) (4 inch/102 mm)
deflection, free-standing, unhoused, laterally stable steel springs. Springs
shall have a lateral stiffness greater than 1.2 times the rated vertical
stiffness and shall be designed for a typical 50% overload to solid. All
springs shall have an polyester powder coated finish and be color coded
to indicate load capacity. Spring coils shall rest on minimum 0.25 inch
(6 mm) neoprene noise pads.
Seismic and wind load restraints shall be designed to limit movement in
all directions. Restraint components shall include neoprene snubbers at
all contact points for energy absorption. There shall be no metal-to-metal
Standard units are designed to withstand a 43 psf horizontal and 25 psf vertical wind load.
Resistance to higher loads or for ratings on extended height curbs or units attached to wood
or concrete will require analysis by KNC, but can in most cases be met with only minor modification.
The vibration isolation curb shall be air and weather tight using an elastomeric
seal, which is attached to the upper support frame with a galvanized steel
clip. The seal shall extend down past the wood nailer of the lower support
assembly and flash over the roof material at the wood nailer on the lower
support curb. The seal shall be Class A, as tested in accordance with approved
Underwriter’s Laboratories, Inc., provisions. Metal or combination metal
and elastomer seals are not permitted. The seal may not be penetrated for
The isolation curb system shall be complete with cross-bracing as required
as a part of the upper and lower assemblies.
Supply and return flex connector support hardware shall be supplied for
installation by the contractor in the field. The supports will be clearly
marked and dimensioned on the submittal and installation drawings. The support
hardware shall be cut-to-length, galvanized steel channels supported and
connected with stamped and punched galvanized steel duct support hangers.
The support hangers shall allow the support elevation to be equal to or
lower than the equipment rail elevation. Supply air and return duct shall
be flexibly attached by the contractor to prevent transmission of vibration
to the building structure.
Airborne noise control packages, if required, shall be supported by the
roof structure within the curb and shall have no rigid contact with the
The isolation curb assemblies shall be shipped to the job site with the
upper support rail, lower support curb, springs and restraints completely
assembled. The contractor shall be required to assemble the four corners,
attach the curb to the roof structure, install cross-bracing and flex connector
supports as necessary, and install and attach rooftop equipment.
Vibration isolators shall be selected by the manufacturer for each specific
application to comply with deflection requirements as shown on the Vibration
Isolation Schedule or as indicated on the project documents.
Roof curb shall be model ESR as manufactured by Kinetics Noise Control, Inc.