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Table 22 Minimum thickness of subflooring Minimum Subflooring Thickness, mm (in.), for Maximum Joist Spacing at 400 (16)
500 (20)
600 (24)
Plywood and OSB, O-2 grade
15.5 (5⁄8)
15.5 (5⁄8)
18.5 (23⁄32)
OSB, O-1 grade, and waferboard, R-1 Grade
15.9 (5⁄8)
15.9 (5⁄8)
19.0 (3⁄4)
Particleboard
15.9 (5⁄8)
19.0 (3⁄4)
25.4 (1)
Panel mark (performance-rated panels) sub-floor only
1F16
1F20
1F24
Panel mark (performance-rated panels) sub-floor and underlay
2F16
2F20
2F24
Lumber
17.0 (11⁄16)
19.0 (3⁄4)
19.0 (3⁄4)
Table 23 Sheathing and subfloor attachment Minimum Length of Fasteners for Sheathing and Subfloor Attachment, mm (in.) Common or Spiral Nails
Ring Thread Nails or Screws
Roofing Nails
Staples
Plywood, OSB or waferboard up to 10 mm (3⁄8 in.) thick
51 (2)
45 (13⁄4)
N/A
38 (11⁄2)
Plywood, OSB or waferboard 10 mm (3⁄8 in.) to 20 mm (13⁄16 in.) thick
51 (2)
45 (13⁄4)
N/A
51 (2)
Plywood, OSB or waferboard over 20 mm (13⁄16 in.) thick
57 (21⁄4)
51 (2)
N/A
N/A
Fibreboard sheathing up to 13 mm (1⁄2 in.) thick
N/A
N/A
44 (13⁄4)
28 (11⁄8)
Gypsum sheathing up to 13mm (1⁄2 in.) thick
N/A
N/A
44 (13⁄4)
N/A
Board lumber 184 mm (8 in.) or less wide
51 (2)
45 (13⁄4)
N/A
51 (2)
2 per support
Board lumber more than 184 mm (8 in.) wide
51 (2)
45 (13⁄4)
N/A
51 (2)
3 per support
Element
Minimum No. or Maximum Spacing of Fasteners
150 mm (6 in.) o.c. along edges and 300 mm (12 in.) o.c. along intermediate supports