existing wood floor joists within 18" of a Type I hood, you have to replace these joists with non-combustible ones?

[Ryan Schultz]

Per the following, if you have existing wood floor joists within 18" of a Type I hood, you have to replace these joists with non-combustible ones? Seems onerous and not what I have anecdotally seen.

Chapter 5: Exhaust Systems, Mechanical Code 2015 of Wisconsin | UpCodes

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507.2.6 Clearances for Type I Hood
A Type I hood shall be installed with a clearance to combustibles of not less than 18 inches (457 mm).
Exception: Clearance shall not be required from gypsum wallboard or 1/2-inch (12.7 mm) or thicker cementitious wallboard attached to noncombustible structures provided that a smooth, cleanable, nonabsorbent and noncombustible material is installed between the hood and the gypsum or cementitious wallboard over an area extending not less than 18 inches (457 mm) in all directions from the hood.

 

[mtlogcabin]

Exception 2 is new maybe your AHJ will allow it under alternate means and methods.

2018 IMC

507.2.6 Clearances for Type I hood.
A Type I hood shall be installed with a clearance to combustibles of not less than 18 inches (457 mm).

Exceptions:

1. Clearance shall not be required from gypsum wallboard or 1/2-inch (12.7 mm) or thicker cementitious wallboard attached to noncombustible structures provided that a smooth, cleanable, nonabsorbent and noncombustible material is installed between the hood and the gypsum or cementitious wallboard over an area extending not less than 18 inches (457 mm) in all directions from the hood.

2. Type I hoods listed and labeled for clearances less than 18 inches in accordance with UL 710 shall be installed with the clearances specified by such listings.