Plain English:
507.2 where Type I is required
Type I hoods are required where appliances produce grease or smoke. That generally means medium-, heavy-, and extra-heavy-duty cooking.
507.2.1 label check
Type I hoods must be labeled with the minimum exhaust flow rate (cfm per linear foot) needed for capture and containment based on duty classification.
507.2.2 extra-heavy-duty restriction
Type I hoods serving extra-heavy-duty appliances cannot cover heavy-, medium-, or light-duty appliances. Also, they must discharge to an exhaust system independent of other exhaust systems.
507.2.3 materials
Minimum construction: Steel: 18 ga min (0.0466 in) OR Stainless: 20 MSG min (0.0335 in)
507.2.4 supports
Noncombustible supports required. Design supports for hood load plus: unsupported grease duct load, effluent loading, and potential personnel loads.
507.2.5 joints and penetrations
Exterior joints/seams/penetrations: continuous external liquid-tight weld/braze to the lowest outermost perimeter.
Interior seams/appendages: not required to be welded, but must be sealed grease-tight.
Exceptions allow listed sealing devices and internal welds if smooth/cleanable.
507.2.6 clearances
Default: 18 in clearance to combustibles.
Exceptions include noncombustible wallboard protection approach and UL 710 listed hoods with reduced clearances (follow listing).
507.2.7 hood portions penetrating ceilings/walls/furred spaces
Must comply with 506.3.11 enclosure requirements. Field-applied grease duct wrap systems (506.3.11.2) cannot be used to satisfy this specific requirement.
On Plans: Why it matters
Typical redlines: "Type I" labeled with no hood listing/label value shown, missing liquid-tight construction notes, 18 in clearance conflicts, and ceiling penetrations drawn with no enclosure strategy.
Code Path: Where to show it
M-001: Type I hood note (materials, liquid-tight exterior, clearance basis, UL 710 listing if applicable, and "penetrations comply with 506.3.11").
M-101/Kitchen elevations: hood type, duty classification, and clearance callouts.
Details: hood-to-wall protection detail where using the gypsum/cement board exception.
Check: Do
Put the hood label info on the schedule (duty + min cfm/lf).
Coordinate clearances early so the architect isn't boxed in later.
Review Risk: Don't
Don't mix appliance duty levels under an extra-heavy-duty hood.
Don't show a ceiling/furred-space penetration without the enclosure approach.
Field Tip:
In your hood schedule, add a "TYPE I CHECK" line: DUTY CLASS + HOOD LABEL (CFM/LF) + MATERIAL (18 GA / SS 20 MSG) + LIQUID-TIGHT EXTERIOR + 18" CLR/UL 710 CLR + PENETRATION (Y/N -> 506.3.11).
Masterbuild QA Lens
Hood material and construction per 507.2.3 must be confirmed against the cooking environment: Type I hoods must be listed, stainless or steel, with welded or gasketed grease-tight construction. Confirm the material, gauge, and grease collection method are on the equipment schedule or detail - not just in Division 11. Material confirmation that contradicts the listing basis will fail.
Drawing / Submittal Check
For Type I hood basics (507.2-507.2.7): the drawings must show the hood construction detail - the listed manufacturer's UL 710 listing or the site-built specification with equivalent materials. Show the grease filter angle and track location. For site-built hoods, show the interior dimensions, the filter bank layout, and the grease drip trough. Type I hood sets without a construction detail or a UL 710 listing reference will not pass first review.
Common Review Risk
Site-built Type I hoods without a UL 710 listing or an approved-equal basis are a common first-cycle comment. IMC 507 requires listed hoods or approval of equivalent construction. The 'equivalent' path requires the AHJ's written approval before the permit set is submitted - not during plan review. Pre-coordinate site-built hood approval with the AHJ before the permit is filed.
When To Escalate
Escalate when the kitchen owner proposes a site-built Type I hood without a UL 710 listing and has not obtained pre-approval from the AHJ. Site-built hoods that arrive at plan review without pre-approval are the most common single source of delay on commercial kitchen mechanical permits. The pre-approval process takes time; start it before the permit is filed.
Load Assumption Check
Type I hood sizing is based on cooking equipment heat input, hood geometry, and overhang distance. Confirm the exhaust CFM calculation uses the actual cooking equipment BTU ratings from the food service equipment schedule, not generic values.
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.