The Ontario Building Code | Coverings or Linings of Ducts
9.10.17.12. Coverings or Linings of Ducts
(1) Where a covering or a lining is used with a duct, such lining or covering shall have a flame-spread rating conforming to Part 6.
9.10.18. Alarm and Detection Systems
In Plain Language
Where a duct has an interior covering or lining, this clause requires that material to meet a flame-spread rating under Part 6, so the duct interior itself doesn't become a path for fire spread.
This is a plain-language summary of the 2012/2017 Ontario Building Code text above, for general understanding only and not a substitute for the Code. Always confirm current requirements against the 2024 edition (O.Reg. 163/24) or a qualified professional before construction.