/ Field knowledge · IMC 506.3.11
Spot wrap is not an enclosure.
If a Type I grease duct punches a ceiling, wall, floor, or any concealed space, IMC 506.3.11 wants it enclosed from that penetration to the outlet. The enclosure serves a single grease duct — no other trades inside. Rating: not less than the penetrated assembly and not less than 1 hour. No fire or smoke dampers in grease ducts. A wrap that only covers the tight spots is not an enclosure.
Educational 2024 International Mechanical Code (IMC) 506.3.10–506.3.12 from Daily Code Talk. Confirm the adopted edition. Distinct from 506.3 construction and 607.5.5 prohibited dampers. This is not an enclosure design. Exception: no enclosure if it only penetrates a non-rated roof/ceiling assembly.
- 506.3.10 underground: 16 ga steel with corrosion coating or 18 ga stainless. Test per 506.3.2.5 before coating or burial. Fully encased in concrete, minimum 4 in thick. Slope toward grease reservoirs. Reservoir plus cleanout at the base of each vertical riser. Horizontal cleanouts on top. Label interior access points.
- 506.3.11: enclose from the penetration to the outlet. Inline fans that are not outdoors are enclosed too.
- 506.3.11.1 shaft: IBC shaft construction. Clearances 18 in to combustibles; 6 in to noncombustible / gypsum on noncombustible framing. Seal at penetrations; vent the shaft to outdoors (weather protected).
- 506.3.11.2 field-applied wrap: listed/labeled system evaluated for grease-duct enclosures (ASTM E2336). Continuous coverage to the outlet. Penetrations: listed firestop (ASTM E814 or UL 1479) with F and T ratings matching the assembly. No spot wrapping just to reduce clearance. Protect wrap from damage.
- 506.3.11.3 factory-built enclosure: listed assemblies (UL 2221) per listing. Penetrations still need listed firestop with matching F and T ratings.
- 506.3.12: a cleanout in a rated enclosure needs a matching fire-rated access panel at each cleanout. Pair with 506.3.8–506.3.9.
Wrap only at the tight joists
Or a fire damper “to be safe” in the grease shaft. Or a cleanout behind gypsum with no rated access panel. Enclosure, prohibited damper, and rated access are three separate first-cycle comments.
Source: Daily Code Talk — IMC 506.3.10–506.3.12 · construction: 506.3 · slope: 506.3.7 · shafts: 607.5.5.
What to send
Where the grease duct punches a ceiling or shaft, whether wrap or a shaft is proposed, and whether cleanouts in that enclosure have rated access panels.
If wrap only covers the tight spots
Send the route. Masterbuild will say whether 506.3.11 still has no continuous enclosure to the outlet — or 506.3.12 still has a cleanout with no rated door.
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. 1-hour enclosure, 18 in / 6 in shaft clearances, ASTM E2336 continuous wrap, UL 2221, 4 in underground concrete, and rated access panels are 2024 IMC 506.3 education from Daily Code Talk — not an enclosure design. This page is not legal advice.