7.1 Type I Hoods: Construction, Clearances & Overhang

Hood & Kitchen Ventilation is 8 percent of the 50-question M2 exam — the largest single task, sitting inside Exhaust & Ventilation (20 percent). Outdoor-air math lives in Table 403.3.1.1. Grease, capture geometry, and suppression live here. Inspectors lose points when they treat the hood as “a kitchen drawing” instead of a Chapter 5 assembly with numbers you can put a tape on.

Chapter 2 defines a Type I hood as a kitchen hood for collecting and removing grease vapors and smoke; such hoods are equipped with a fire suppression system. A Type II hood is a general kitchen hood for steam, vapor, heat, odors, and products of combustion. Commercial cooking appliances are appliances used in a commercial food-service establishment — food prepared for sale, or prepared on a volume and frequency that is not domestic household cooking. A church warming kitchen that deep-fries twice a week is still commercial cooking.

507.1 is the first sentence you tab: hoods shall be Type I or Type II and shall capture and confine cooking vapors and residues. Install Type I at or above appliances per 507.2. Install Type II at or above appliances per 507.3. Where any cooking appliance under a single hood requires a Type I hood, a Type I hood shall be installed. Where Type II is required, Type I or Type II may be installed. One 40-pound fryer under a 16-foot canopy that also covers a pasta cooker makes the entire canopy Type I — grease duct, UL 1046 filters, 18-inch clearance, and suppression included.

When 507.2 forces Type I

507.2: Type I hoods shall be installed where cooking appliances produce grease or smoke as a result of the cooking process. Type I hoods shall be installed over medium-duty, heavy-duty, and extra-heavy-duty cooking appliances. Light-duty equipment that still produces grease or smoke (a conveyor pizza oven is medium-duty; a greasy broiler is heavy-duty) does not get a Type II discount because the nameplate says “oven.”

Use the Chapter 2 duty definitions, not the salesperson’s brochure:

A gas griddle is medium-duty. An electric open fryer is medium-duty. A wok range is heavy-duty. A stick-burner under a hood is extra-heavy-duty. Field fail: a fryer, charbroiler, or wok slid under a Type II condensate hood “because the rest of the line is steamers.”

Canopy versus backshelf (proximity)

Chapter 2 names the shapes you will see on a plan:

• Wall canopy — mounted against a wall (or a back panel) above a line of appliances; overhangs the front and the open sides. The wall forces makeup air across the front of the equipment.
• Single island canopy — open on all sides over a single line; more vulnerable to cross-drafts, so 507.2.10 / 507.3.4 demand more cfm per linear foot than a wall canopy.
• Double island canopy — over back-to-back lines; rates are published per side.
• Backshelf / pass-over / low-proximity — front lower lip sits low and is set back from the appliance front; always closed to the rear. A pass-over is a free-standing backshelf low enough to hand food over.
• Eyebrow — mounted to the face of an oven or dishwasher above the door, overhanging the opening.

507.1.6.1 Canopy size and location (Type I and Type II): the inside lower edge shall overhang or extend a horizontal distance of not less than 6 inches (152 mm) beyond the edge of the top horizontal surface of the appliance on all open sides. The vertical distance between the front lower lip of the hood and that cooking surface shall not exceed 4 feet (1219 mm). Exception: the hood may be flush with the outer edge of the cooking surface where the hood is closed to that appliance side by a noncombustible wall or panel.

Measure the appliance’s top horizontal surface, not the drip pan and not the splash. A 36-inch-deep range under a wall canopy needs 6 inches past the front (and past any open end). A 5-foot lip-to-griddle dimension fails even if the cfm label is huge.

507.1.6.2 Noncanopy (backshelf) size and location: the hood shall be located not greater than 3 feet (914 mm) above the cooking surface, and the edge of the hood shall be set back not greater than 1 foot (305 mm) from the edge of the cooking surface. A backshelf hung at 42 inches with a 16-inch setback fails both numbers.

507.1.5: each exhaust outlet inside the hood shall serve not more than a 12-foot section of hood. A 20-foot canopy with one collar is a capture fail waiting for 507.1.7.

Construction, joints, supports, filters at the hood

507.2.3 Type I materials: steel not less than 0.0466 inch (1.181 mm) (No. 18 gage) or stainless steel not less than 0.0335 inch (0.8525 mm) (No. 20 MSG). That is thicker than a Type II hood (22/24 gage) and thinner than a field-welded grease duct (16/18 gage). Do not mix the three gages on a stem.

507.2.5: external hood joints, seams, and penetrations shall be a continuous external liquid-tight weld or braze to the lowest outermost perimeter of the hood. Internal joints, filter frames, and appendages need not be welded if they are otherwise sealed grease tight. Listed penetration devices are excepted. Internal welds are allowed if formed or ground so they do not trap grease and are readily cleanable. Pop rivets and raw sheet-metal screws on the grease plenum fail 507.2.5.

507.2.4: Type I supports shall be noncombustible and adequate for the hood, the unsupported grease duct, effluent loading, and personnel working on the hood. Unistrut hung from wood joists with no calculation is not an answer.

507.2.8 / Table 507.2.8: Type I hoods shall have grease filters listed and labeled to UL 1046, accessible for cleaning or replacement. Lowest filter edge above the cooking (or heating) surface: 0.5 foot without exposed flame, 2 feet with exposed flame and burners, 3.5 feet for exposed charcoal and charbroil. 507.2.8.2: filters at not less than 45 degrees from horizontal, with a drip tray under the lower edge. Ordinary mesh filters do not carry a UL 1046 listing; NFPA 96, which the 2024 IBC/IFC commercial-cooking extinguishing section requires you to follow, prohibits mesh. A mesh panel in a Type I hood is a fail.

507.2.6 Clearances for Type I hood: not less than 18 inches (457 mm) to combustibles. Exceptions: (1) gypsum wallboard or ½-inch-or-thicker cementitious wallboard on noncombustible structure, with a smooth, cleanable, nonabsorbent, noncombustible material between the hood and the board extending not less than 18 inches in all directions from the hood; (2) Type I hoods listed and labeled for less than 18 inches in accordance with UL 710, installed at the listed clearance. A hood shoved to a wood-stud, vinyl-covered wall is an 18-inch fail. A UL 710 hood labeled “0-inch to limited combustibles” is not an 18-inch fail.

507.2.7: a Type I hood (or portion) that penetrates a ceiling, wall, or furred space shall comply with 506.3.11. Field-applied grease-duct wrap (506.3.11.2) shall not be used to satisfy 507.2.7.

Recirculating systems and the “no hood” list

507.1 Exception 2.1 is the recirculating path: factory-built commercial cooking recirculating systems listed and labeled to UL 710B and installed per 304.1 do not require a hood. The room is still a kitchen for Table 403.3.1.1; each appliance is not less than 100 square feet for that outdoor-air/exhaust math. 501.3 Exception 2 lets those systems skip outdoor discharge. A field-built charcoal filter box on a Type II hood is not UL 710B.

507.1 Exception 1 is the UL 710 factory-built exhaust-hood shortcut: a listed factory-built hood installed per 304.1 need not comply with 507.1.5, 507.1.6, 507.2.3, 507.2.5, 507.2.8, 507.2.10, and 507.3.1. It is still a hood. It does not become a recirculating unit.

507.1.2: domestic cooking appliances used for commercial purposes get Type I or Type II as 507.2 / 507.3 require. Domestic appliances used for domestic cooking go to Section 505. A residential microwave hood over a restaurant fryer fails 507.1.2.

507.1.3: appliances with draft hoods or atmospheric burners shall not sit in the same room as a Type I or Type II hood unless they are in a sealed enclosure with a self-closing device and combustion air from outdoors or from other spaces per Chapter 7 / IFGC. A water heater with a draft hood in the kitchen is a separate fail from the hood itself.

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