Does Replacing a Rooftop HVAC Unit Need a PE Stamp?

The structural review starts with the load comparison: new unit operating weight versus old, curb weight, and the resulting point loads on the roof framing. I verify the existing structure's capacity from the structural drawings — member sizes, spans, design loads — and check the new loads against it, including the code's required load combinations. Where drawings are missing or the roof's history is uncertain, field verification establishes the framing before I rely on it. Concentrated equipment loads punish optimistic assumptions, so the verification is conservative by design. The curb analysis follows. For a new curb, I design the curb framing, its support on the roof structure, and the anchorage for gravity, wind, and seismic forces. For a reused curb, I verify dimensional compatibility with the new unit, structural condition, and anchorage adequacy under current code — and I state plainly when a curb that's served for twenty years doesn't meet today's anchorage requirements. Roof condition gets noted too: the membrane's remaining life and the drainage around the new curb location, because a structurally perfect installation on a failing roof is still a problem the owner should know about.

Equipment anchorage is the life-safety core of the RTU review. In seismic jurisdictions — California, Nevada, and the seismic zones of other states — I design the anchorage for the site's seismic forces: unit-to-curb connections, curb-to-structure connections, each with calculated demands and detailed capacities. The load path has to be complete and traceable: the seismic force on the unit travels through the anchorage into the curb, through the curb connections into the roof framing, and the framing has to be verified for those added point loads. Flexible connectors on the duct, piping, and conduit let the restrained unit move without tearing its connections apart. In high-wind markets — Florida, the Gulf Coast, Texas — wind uplift and lateral wind on the unit govern instead. The anchorage resists the code's wind pressures on the unit as a rooftop component, with the curb and its connections designed for the uplift. Either way, the sealed calculations show the demands, the connection details show the capacities, and plan check can trace the unit's stability from the equipment schedule to the roof framing without asking for more.

An RTU replacement submittal is ready for the PE's seal when the weight comparison, the structure, and the anchorage are all resolved. The curb detail earns the closest look — it's the most corrected item. • New vs old unit weights documented: operating weight, footprint, curb compatibility confirmed • Existing roof structure verified — drawings or field verification — for the new concentrated loads • Curb designed (new) or verified (reused) for weight, wind, and seismic with current-code anchorage • Seismic anchorage detailed for the site's criteria in CA/NV; wind uplift anchorage in FL/TX/Gulf markets • Mechanical coordination: duct, electrical, and drainage connections verified for the new unit • Flexible connections on ductwork, piping, and conduit where seismic anchorage restrains the unit