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Apprentice answer

What is the required clearance to combustibles for a Type 1 grease duct (black iron)

3rd YearGrease Duct & Specialty ExhaustStop / Verify

Per the International Mechanical Code (IMC Section 506), a standard, uninsulated Type 1 commercial kitchen grease duct must maintain a strict minimum of 18 inches of clearance to any combustible materials (like wood framing or drywall).

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Plain-English answer

Per the International Mechanical Code (IMC Section 506), a standard, uninsulated Type 1 commercial kitchen grease duct must maintain a strict minimum of 18 inches of clearance to any combustible materials (like wood framing or drywall).

The Fix: This clearance can only be reduced if you wrap the duct in an ICC-ES listed field-applied multi-layer fire barrier blanket system (like 3M Fire Barrier or FireMaster wrap).

Field checklist

Ask Foreman

Hey boss, I’m on specialty duct and need verification before I touch this: What is the required clearance to combustibles for a Type 1 grease duct (black iron)? Do you want me to stop here and check the approved detail, submittal, or inspector/manufacturer requirement first?

Verify before acting

Use this as training guidance. The foreman, approved drawings, project specs, manufacturer installation instructions, employer safety policy, and AHJ/code requirements always control the final answer.

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