Rooftop Unit Replacement Without Permit Revision
A contractor is replacing a 12-year-old packaged rooftop unit serving a small office suite. The original permit, issued 14 months ago, covered a like-for-like swap of a 5-ton unit at 2,000 cfm. During removal the crew finds the roof curb is 3 inches too narrow for the selected replacement and the existing gas supply line is 1/2-inch nominal, while the new unit's nameplate calls for a 3/4-inch connection. The mechanical inspector has already performed one rough-in inspection on the original scope. The contractor proposes to field-fabricate a curb adapter from unlisted sheet metal, run a new gas line from the meter, and proceed without contacting the building department because the total connected load is unchanged. The building is a single-story Type V-B occupancy with a 6-foot clearance to the property line.
1. Evaluate whether the contractor's plan to proceed without a permit revision is defensible, and identify the specific administrative failures.
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The plan is not defensible. A permit is scope-specific; changing the appliance, the curb, and the fuel-gas piping is a change to the approved construction documents, and most codes require the permit holder to submit revised drawings before proceeding when the work deviates from the approved plans. The field-fabricated curb adapter is an unlisted component installed in the building envelope and air-distribution path - it needs to be evaluated as part of the revised submittal, not improvised.
The 'connected load is unchanged' argument fails because the fuel-gas branch line is being replaced: sizing, materials, and the new appliance's input rating all matter, and the gas piping is a separate regulated system even if total Btu input is identical. Running new gas line from the meter also implicates the serving utility and possibly the meter/regulator sizing.
Administrative failures: (1) proceeding without revised plans, (2) installing unlisted equipment without approval, (3) altering fuel-gas piping without inspection, (4) not notifying the department of a change that affects the rough-in already inspected.
2. The contractor argues the curb adapter is 'just sheet metal' and outside mechanical scope. How should the inspector classify it, and what does that classification require?
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The adapter is part of the air-distribution system - it forms the transition between the rooftop unit discharge/return and the building ductwork, so it falls within the mechanical scope rather than being incidental building envelope work. As a duct/plenum component it must be of approved material and construction, and where it functions as part of the supply plenum it must meet the same requirements as the duct system it connects to (material, thickness/gauge, and closure).
If it is field-fabricated, the inspector should require submittal of the fabrication details and verify that the material and joints are suitable for the application, that it is sealed, and that it does not create an unsealed path between the return and supply. The inspector should not accept 'it's just sheet metal' as a basis for skipping review; the correct path is a revised submittal showing the adapter, followed by inspection before the unit is set and connected.