P Series Curbs are high quality, structural tubular steel support systems for rooftop unit vibration isolation abatement and seismic/wind restraint. Each custom-built unit incorporates both the roof curb and spring isolation into one complete structure. VMC engineers design each curb to custom fit any rooftop mechanical equipment. 

P6200 2" Spring Isolation Curbs can be specified to compensate for large floor spans, and spring pockets are positioned within the curb at the correct load points for proper support and seismic restraint. All spring pockets incorporate a minimum 1/4" elastomeric cup or pad in series with the spring to provide optimum isolation efficiency.   

The curb and rooftop unit can be fully installed and adjusted before the roof is sealed. 

Spring pockets are accessible from around the outside of the curb. All springs are color-coded for ease of identification, and any spring can be removed and replaced while the rooftop unit is installed. Once adjusted and leveled, the rooftop unit becomes free floating - completely isolated from the building structure, while completely restrained to it.  

P Series roof curbs are fabricated from force-resisting structural steel specifically designed to withstand seismic and high wind forces. Unlike standard curbs that typically come with a rooftop handling unit, or sheet metal curbs incorporating a seismic isolator, the VMC rooftop support systems combine our seismic spring design within a moment resisting frame. Our high strength frame is capable of direct, positive attachment to both the building structure and the roof mounted equipment while each spring pocket provides vibration isolation and both seismic and wind restraint. Standard sheet metal curbs that typically come with rooftop equipment are not capable of resisting these forces and do not allow for direct, positive attachment to the roof structure and mechanical equipment. Our high strength frame can be bolted or welded to the roof's structural steel and will not break away during an earthquake or high wind forces. Sheet metal curbs cannot accept point-loading of these forces and will tear away from the building structure due to their thin construction. 

Features & Benefits

  • Sound (TAS) control system that attenuates heat and noise
  • Offers a more efficient, quieter, and user-friendly system
  • National Roofing Contractor Association (NRCA) design compliant
  • Works well with all roofing
  • Seismic hold down ensures equipment is positively attached to the curb
  • Structural steel construction facilitates positive connection to the building structure


  • HVAC rooftop equipment such as RTU's and fans




The engineers we employ hold the highest industry-recognized credentials in structural analysis, elastomer development and system dynamics.


We are the first ISO accredited PCA ISO-17065, third-party certification body for special seismic certification of non-structural building components and their mounting configurations by the ICC’s International Accreditation Service.

Test & Measurement

We are the only ISO 17025:2005 Accredited Seismic Simulation Test Laboratory with a triaxial shake table owned and operated by California licensed Structural engineers.

Testing Services Update
DCL now offers Nuclear Qualification and Testing services.

In partnership with Greenberry Industrial, we now offer testing services that meet the requirements of ASME NQA-1.

Call for more information.