Domestic kitchen exhaust looks simple until you have big hoods, tight envelopes, or multistory shafts. IMC 505 is where "just a range hood" becomes a real exhaust system with listings, duct rules, and makeup air.
We'll cover 505 in three parts:
Part 1 (505.1-505.3): Equipment, listings, and ducts
How domestic cooking exhaust equipment is listed (UL 507, UL 858, UL 923, ANSI Z21.1), when ductless hoods are allowed, what duct materials are permitted, smooth airtight ducts with backdraft dampers, and the special case where downdraft systems can use PVC under a slab.
Part 2 (505.4-505.5): Makeup air and common multistory systems
When makeup air is required for hoods over 400 cfm and how it must be interlocked. Common domestic kitchen exhaust shafts in multistory buildings: fire-rated shaft, straight 26-gauge rigid duct, fan outside the airstream on standby power, no dampers or screens, cleanout at the base, and the shaft serving only kitchen exhaust.
Part 3 (505.6-505.8): Other than Group R, Group I-1 and I-2
When "domestic" cooking used in non-residential occupancies still needs domestic exhaust systems, plus the 500 cfm minimum hood rate in I-1 and I-2, outdoor discharge, and the limited ductless hood exception with charcoal filters.
On Plans: Why it matters
Common plan-review hits: calling something "domestic" but routing it like a commercial hood, no makeup air on big island hoods, common shafts drawn with offsets or dampers, and I-1/I-2 kitchens using undersized or recirculating hoods that do not meet the 500 cfm and discharge requirements.
Code Path: Where to show it
M-001: "IMC 505 DOMESTIC COOKING EXHAUST" note listed equipment, ducts to outdoors (or listed ductless), makeup air for hoods >400 cfm, and rules for any common multistory shaft.
M-101: Range hood locations, duct routing, duct type callouts, and termination locations.
M-601: Simple hood / domestic kitchen exhaust schedule with HOOD CFM, DUCT SIZE/MATERIAL, MAKEUP AIR (Y/N), COMMON SHAFT (Y/N), and CODE REF (505.x).
Check: Do
Coordinate hood cfm, duct path, and makeup air with the architect and structural so the route, shaft, and openings are all realistic.
Review Risk: Don't
Treat large domestic hoods or multistory shafts as "just another exhaust line."
Field Tip:
Add a "DOMESTIC KITCHEN EXHAUST-IMC 505 CHECK" box in your template: equipment type/listing, hood cfm, duct route and termination, makeup air needed (Y/N), common shaft (Y/N), Group R vs I-1/I-2. If every line is filled before you issue, you've already answered most reviewer questions.
Masterbuild QA Lens
Domestic range exhaust is one of the most frequently incorrect systems in residential mechanical submittals. The most common redlines: ductless hood used where exterior duct is required by the design; duct exceeds 35 ft equivalent length without documented exception; and termination cap allows re-entry of exhaust. Confirm exterior duct routing, material, length, and termination type before submitting.
Drawing / Submittal Check
M-001 must identify the occupancy type for each cooking exhaust system: residential (R-2, R-3) under IMC 505 vs. commercial cooking under IMC 506/507. Residential cooking exhaust to the exterior vs. recirculating-type must be called out - IMC 505 permits recirculating only in specific conditions. Where residential cooking exhaust exits through fire-rated assemblies, confirm no fire damper is required.
Common Review Risk
The most common 505
When To Escalate
Escalate for large residential cooking exhaust systems (over 400 CFM) in high-rise buildings where makeup air is not feasible from the exterior, and for institutional kitchen cooking exhaust in I-1 or I-2 occupancies where the design team is uncertain whether the system qualifies as domestic or commercial cooking exhaust. The classification determines the entire system design.
Rated Assembly Coordination
Domestic cooking exhaust duct penetrations through fire-rated assemblies are common in multifamily buildings with stacked unit layouts. Confirm damper or firestop type at each rated floor and wall crossing before the duct riser is drawn.
Load Assumption Check
Domestic cooking exhaust CFM is determined by hood size and appliance type. Confirm the exhaust rate before selecting the makeup air unit - undersized makeup air creates negative pressure that degrades hood capture performance.