Flame Spread

Stairwell from 2nd Floor 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
Materials	Applicable Standard	Minimum Thickness mm	FSR	SDC	FSR	SDC
Hardwood or softwood flooring³	-	-	300	300
Gypsum wallboard	CSA A82.27-M⁴	9.5	25	50	25	50
Lumber	None	16	150	300	150	300
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, Type1	CAN/CGSB-11.3-M	9	150	> 300	²	²
Hardboard,Standard	CAN/CGSB-11.3-M	6	150	300	150	300
Particleboard	ANSI A208.1	12.7	150	300	²	²
Waferboard	CAN3-O437.0	-	²	²	²	²
OSB	CAN/CSA-O325	-	²	²	²	²
Notes: The flame-spread ratings and smoke developed classifications shown are for those plywoods without a cellulose resin overlay. Insufficient test information available. Wood flooring unfinished or finished with a spar or urethane varnish coating Gypsum Wallboard complying with the following ASTM standards is also acceptable - ASTM C1396/C, ASTM C1396M. Flame-spread ratings and smoke developed classifications for paints and varnish are not applicable to shellac and lacquer. Flame-spread ratings and smoke developed classifications for paints apply only to alkyd and latex paints.
*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
Product Lumber, 19mm thickness		Flame-Spread Ratings	Smoke Developed Classification
Cedar	Western Red	73	98
Cedar	Pacific Coast Yellow	78	90
Fir	Amabilis (Pacific Silver)	69	58
Hemlock	Western	60-75
Maple	(flooring)	104
Oak	red or White	100	100
Pine	Eastern White	85	122
	Lodgepole	93	210
	Ponderosa	105-230
	Red	142	229
	Southern Yellow	130-195
	Western White	75
Poplar		170-185
Spruce	White	65
	Sitka	74	74
	Western	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.

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Canadian Wood Council Members