Type II hoods are not "grease ducts," but the exhaust still has to be built and terminated like a real system, not a loose note on the plan.
Plain English:
506.4 scope: Commercial kitchen exhaust serving Type II hoods must follow 506.4.1 and 506.4.2.
506.4.1 ducts
Ducts and plenums must be rigid metallic.
Construction, install, bracing, and supports follow Chapter 6.
If the duct is under positive pressure or carries moisture-laden or waste-heat-laden air, it must be constructed, joined, and sealed in an approved manner.
506.4.2 terminations: Terminate per the hood manufacturer and also meet these placement rules:
Minimum 3 ft from openings into the building.
Minimum 10 ft from property lines or buildings on the same lot.
Minimum 10 ft from outside air intake.
Minimum 10 ft above grade.
If above roof: minimum 30 in above roof surface.
Minimum 30 in from exterior vertical walls.
Protect against local weather.
Do not discharge onto walkways.
Meet IBC requirements for exterior wall opening protectives.
On Plans: Why it matters
Common redlines: nonmetal duct called out, no sealing shown for positive pressure runs, and terminations too close to doors, windows, intakes, property lines, or pedestrian paths.
Code Path: Where to show it
M-001: "TYPE II HOOD EXHAUST" note stating rigid metallic ductwork, Chapter 6 construction, and sealing for positive pressure or moisture or heat laden runs.
M-101: Duct routing plus a clear termination callout with distances to openings, grade, walls, and property line where applicable.
Roof plan or exterior elevation: Outlet location and discharge direction, with "DO NOT DISCHARGE TO WALKWAYS" where it could be a conflict.
Check: Do
Treat Type II exhaust as a fully detailed duct system, not a generic exhaust arrow.
Show termination clearance compliance on the drawings, not only in specs.
Review Risk: Don't
Don't use flex or nonmetal duct for Type II hood exhaust.
Don't place the outlet where it can recirculate to openings or create a nuisance at sidewalks.
Field Tip:
Before you finalize the roof plan, run a quick "3-10-10-10-30" check for every Type II outlet: 3 ft from openings, 10 ft from property lines or same-lot buildings, 10 ft from outside air intakes, 10 ft above grade, 30 in above roof and 30 in off walls. If any one is tight, relocate the outlet now, not during inspection.
Masterbuild QA Lens
Grease duct routing above the kitchen ceiling must account for access for inspection and cleaning - not just structural clearance. Confirm the isometric shows duct pitch to drain (minimum 1/4 in per foot toward the cooking equipment), all cleanout locations, and the grease collection point. A duct that drains back into the equipment is a fire hazard that will be caught at inspection.
Drawing / Submittal Check
For Type II hood ducts and terminations: the drawings must distinguish Type I grease duct from Type II lower-heat duct on both the plan and the schedule. Type II duct has lighter construction requirements, but if it serves a cooking appliance that produces grease-laden vapors, it must comply with Type I requirements regardless of hood type. Confirm the appliance list drives the hood type.
Common Review Risk
The most common Type II hood error is serving a cooking appliance that produces grease-laden vapors under a Type II hood. The appliance type determines the required hood type - not the design intent. A Type II hood over a commercial fryer is a code violation regardless of the hood label. Confirm the appliance schedule before the hood type is specified.
When To Escalate
Escalate when the appliance list for a kitchen project is not finalized before the permit is filed, resulting in uncertainty about whether Type I or Type II hoods are required. A hood system designed for Type II that is later upgraded to Type I requires a duct replacement, a fire suppression system addition, and a permit amendment - an expensive change. Confirm the appliance list before the permit.
Load Assumption Check
Type II hood duct systems are sized for lower exhaust rates than Type I systems. Confirm the hood classification is correct before sizing the duct - an incorrect hood type assumption changes exhaust CFM, duct size, and fan selection.
Kitchen Exhaust Coordination
For kitchen exhaust, tie the hood schedule, appliance lineup, grease duct route, cleanouts, fan discharge, fire suppression interface, and make-up air strategy into one reviewable story.