Why does a rooftop unit need a level curb on a sloped roof

Plain-English answer

Rooftop equipment usually needs the top of the curb level even when the roof deck is pitched. If the curb follows the slope, pans, drains, fan sections, doors, and internal components may not work as intended.

The fix is best before the unit is set: verify roof pitch, curb submittal, manufacturer requirements, and whether a factory or field pitch adapter is required. If the unit is already set, do not shim casually under equipment without approved direction.

Field checklist

• Measure roof pitch and check whether the curb top is level both directions.
• Check the RTU/AHU/curb submittal for pitch adapter or level tolerance requirements.
• Confirm condensate drain pan direction and drain outlet side.
• Coordinate with roofing/structural/GC if curb modification affects flashing or support.
• Fix before crane set when possible.

Ask Foreman

Verify before acting

Use this as training guidance. The foreman, approved drawings, project specs, manufacturer installation instructions, employer safety policy, and AHJ/code requirements always control the final answer.

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