Any material that forms part of the building interior and is directly exposed is considered to be an interior finish. This includes interior claddings, flooring, carpeting, doors, trim, windows, and lighting elements.
If no cladding is installed on the interior side of an exterior wall of a building, then the interior surfaces of the wall assembly are considered to be the interior finish, for example, unfinished post and beam construction. Similarly, if no ceiling is installed beneath a floor or roof assembly, the unfinished exposed deck and structural members are considered to be the interior ceiling finish.
The flame-spread rating and smoke developed classification of a material can be determined from the information contained in Appendix D of the NBCC, Division B.
Information is only provided for generic materials for which extensive fire test data is available (Table 2). For instance, lumber, regardless of species, and Douglas fir, poplar, and spruce plywood, of a thickness not less than those listed, are assigned a flame-spread rating of 150.
|Table 2: Assigned flame-spread ratings and smoke developed classifications|
|Materials||Applicable Standard||Minimum Thickness mm||Unfinished 3||Paint or Varnish not More than 1.3mm Thick, Cellulosic Wallpaper not more than 1 Layer 5,6|
|Hardwood or softwood flooring3||-||-||300||300|
|Gypsum wallboard||CSA A82.27-M4||9.5||25||50||25||50|
|Douglas Fir plywood1||CSA O121||11||150||100||150||300|
|Poplar plywood1||CSA O153||11||150||100||150||300|
|Plywood with Spruce face veneer1||CSA O151||11||150||300||150||100|
|Douglas Fir plywood1||CSA O121||6||150||100||150||100|
|Fiberboard low density||CAN/ULC-S706||11||> 150||100||150||100|
|Hardboard, Type 1||CAN/CGSB-11.3-M||9||150||> 300||2||2|
|Source: Appendix D, Section D-3, 2010 NBCC Division B|
In general, for wood products up to 25mm thick, flame-spread rating decreases with increasing thickness. Values given in the Appendix D of the NBCC are conservative because they are intended to cover a wide range of materials. Specific species and thicknesses may have values much lower than those listed in Appendix D.
Specific ratings by species are given in Table 3 below. Information on proprietary and fire-retardant materials is available from ULC listings or from manufacturers. The values listed in Table 3 apply to finished lumber, however, there has been no significant difference in flame-spread rating noted in rough sawn lumber.
|Table 3: Typical flame-spread ratings and smoke developed classifications of wood products|
Lumber, 19mm thickness
|Flame-Spread Ratings||Smoke Developed Classification|
|Pacific Coast Yellow||78||90|
|Fir||Amabilis (Pacific Silver)||69||58|
|Oak||red or White||100||100|
|Shakes||Western Red Cedar||69|
|Shingles||Western Red Cedar||49|
|Source: Fire Safety Design in Buildings, 1995|
The American Wood Council has additional information on Design for Code Acceptance of Flame Spread Performance of Wood Products in the U.S.