/ Field knowledge · IMC 506.5
An upblast without a hinge and a grease drain will fail inspection.
Type I exhaust equipment is not a generic rooftop fan. IMC 506.5: the housing is built like a grease duct unless the fan is listed to UL 705. The motor stays outside the exhaust airstream. Upblast fans: hinged, flexible weatherproof electrical cable, and a restraint. Grease duct extends at least 18 in above the roof. Vertical discharge needs a drain at the low point to an approved grease reservoir. Upblast without a drip tray and grease drain is the most common 506.5 inspection failure.
Educational 2024 International Mechanical Code (IMC) 506.5–506.5.6 from Daily Code Talk. Confirm the adopted edition. Distinct from 506.3.13 termination and 506.3 duct. This is not a fan selection.
- 506.5.1: Type I exhaust-fan housing built like a grease duct (506.3.1) unless listed to UL 705. Motor outside the airstream. In-line fan not outdoors: room or space with the same fire-resistance rating as the grease-duct enclosure, with service access and ventilation per the manufacturer.
- 506.5.2 pollution-control units (PCU): UL 8782 listed PCU, UL 705 listed fan, noncombustible supports, indoor units listed for indoor use, clearances per listing. Indoor with enclosed grease duct: dedicated rated enclosure equal to the duct-enclosure rating. Roof-mounted units at least 18 in above the roof. Discharge per 506.3.13. Pressure-drop monitoring with a visual alarm in the cooking area when airflow drops below design. Factory fire suppression. Wash-down drains to a grease interceptor with a trapped or sealed drain.
- 506.5.3: discharge cannot impinge on roof, equipment, or structure. Vertical discharge fans: drain outlet at the low point to an approved grease reservoir.
- 506.5.4 upblast mounting: hinged fan, flexible weatherproof electrical cable, and a restraint. Grease duct at least 18 in above the roof.
- 506.5.5: 18 in to combustibles unless listed for less. 506.5.6: termination per 506.3.13. Parapet exception: 2 ft minimum if the parapet is not higher than the top of the discharge opening.
Motor in the airstream, no hinge, no grease drain
Or discharge blasting the roof. Or a PCU with no cooking-area alarm and no interceptor drain. Those are first-cycle comments and failed roof inspections.
Source: Daily Code Talk — IMC 506.5 · termination: 506.3.13 · enclosure: 506.3.11 · overhang: 507.1.6.
What to send
The fan cut sheet, roof plan (hinge, drain, discharge direction), and whether a pollution-control unit is proposed.
If the upblast has no hinge, cable, or grease drain
Send the roof plan and the fan. Masterbuild will say whether 506.5.4 still has no service path — or 506.5.1 still has a motor in the airstream.
Send Project Background+1 (786) 398-6940 · osmany.portal@masterbuildconsulting.com
Masterbuild provides engineering services under a written scope. Nothing on this page is project-specific engineering advice, a code interpretation for your project, or a representation about permit approval. Confirm the adopted edition. UL 705, motor out of the airstream, 18 in above the roof, hinge/cable/restraint, PCU UL 8782, and the grease-reservoir drain are 2024 IMC 506.5 education from Daily Code Talk — not a fan design. This page is not legal advice.