Plain English:
506.3.10 underground grease ducts
Materials: 16 ga steel with corrosion coating, or 18 ga stainless.
Test before burial: test per 506.3.2.5 prior to coating or placing in ground.
Encase in concrete: fully encased, min 4 in thick.
Slope toward grease reservoirs.
Reservoir + cleanout: at base of each vertical riser.
Cleanouts: provide per 506.3; horizontal cleanouts go on TOP.
Identify access: label cleanout locations at interior access points.
506.3.11 grease duct enclosures
If a Type I grease duct penetrates a ceiling, wall, floor, or any concealed space, enclose it from penetration to outlet.
Inline fans not outdoors: enclose them too.
Duct 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/smoke dampers in grease ducts.
Exception: no enclosure required if it only penetrates a non-rated roof/ceiling assembly.
506.3.11.1 shaft option
IBC shaft construction.
Clearances: 18 in to combustibles; 6 in to noncombustible/gypsum on noncombustible framing.
Seal at penetrations; vent shaft to outdoors (weather protected).
506.3.11.2 field-applied wrap option
Listed/labeled system evaluated for grease duct enclosures (ASTM E2336).
Continuous coverage to 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 option
Listed enclosure assemblies (UL 2221) installed per listing.
Penetrations still need listed firestop with matching F and T ratings.
506.3.12 rated access to cleanouts
Cleanout in a rated enclosure = provide matching fire-rated access panel at each cleanout.
Sign req'd: "ACCESS PANEL. DO NOT OBSTRUCT."
On Plans: Why it matters
Common failures: burying duct with no test/encasement, missing reservoir/cleanout plan, "shared" shafts with other trades, wrapped duct with no rated access panels.
Code Path: Where to show it
M-001: note enclosure method (SHAFT vs WRAP vs FACTORY-BUILT), rating basis, and "NO DAMPERS."
M-101/M-601: identify underground runs, note "4 IN MIN CONCRETE ENCASEMENT," show slope arrows, and tag reservoirs + cleanouts.
Check: Do
Choose enclosure method early and coordinate clearances and access.
Tag every cleanout and show the access panel when enclosed.
Review Risk: Don't
Don't bury grease duct without testing and 4 in concrete encasement.
Don't hide cleanouts in shafts/wrap without rated access panels.
Field Tip:
Do an "ACCESS TRACE" on plans: hood to outlet. Every cleanout must have a tag and a reachable access panel. If you can't point to it on the sheet, the field won't find it.
Masterbuild QA Lens
Grease duct penetrations through rated assemblies require a listed enclosure or listed through-penetration system - not a standard firestop. Confirm the assembly type is shown at every rated penetration on the floor plan and that the UL design number for the listed system is in the materials schedule. Coordinate with the fire-protection engineer before submittal.
Drawing / Submittal Check
For 506.3.10-506.3.12 (grease reservoirs, cleanouts, access): the drawings must show the cleanout and reservoir locations at the low points of the duct system. For horizontal duct runs, show the slope direction and the reservoir location at the low point. Show access panel locations on the plan. Access details that show only the panel size without the required minimum clearance in front of the panel will get a comment.
Common Review Risk
Grease cleanout access is the most common inspection failure on grease exhaust systems. IMC 506 requires access at every change of direction and at maximum 20-foot intervals. When the duct routing passes through concealed spaces, access panels must be provided in the ceiling or wall. Ceilings that are finished before the grease duct access is verified will require opening for each missing access panel.
When To Escalate
Escalate when the grease duct access panel locations conflict with architectural finishes or tenant lease boundaries in a multi-tenant building. Access panel locations in leased commercial kitchen spaces are a coordination problem between the landlord, the tenant, the mechanical engineer, and the AHJ - all four must agree before construction.
Rated Assembly Coordination
Sections 506.3.10-506.3.12 address grease duct clearances through rated floors and ceilings. At each floor penetration, confirm the enclosure extends through the assembly and that the rated ceiling integrity is maintained below the grease duct.
Load Assumption Check
Sections 506.3.10-506.3.12 govern grease duct clearances and floor penetrations, which can lengthen the duct route. Recheck static pressure and fan selection if the code-required clearances force a longer or more restrictive duct path than the original layout.