Tables 2: Span Tables for Joists
These joist span tables are taken from the National Building Code of Canada, 1998 BC Edition (still current) and are for reference only. The final authority in building codes, including joist spans, lies with the building inspector in your local area. To improve the span of floor joists it is recommended to use 5/8" tongue and groove standard sheathing grade sub-floor, glued and screwed, with bridging between the joists and strapping below the joists. If the ceiling is finished below the floor, drywall is considered strapping.
Maximum Spans for Floor Joists in Living Quarters
Span in feet-inches using #2 and better
| Species | Dimension | Spacing of Joists with Strapping and Bridging | ||
|---|---|---|---|---|
| 12" | 16" | 24" | ||
| Hemlock Fir | 2x4 | 6'-10 | 6'-2 | 5'-5 |
| 2x6 | 10'-9 | 9'-9 | 8'-7 | |
| 2x8 | 13'-9 | 12'-9 | 11'-3 | |
| 2x10 | 15'-10 | 14'-9 | 13'-9 | |
| 2x12 | 17'-9 | 16'-7 | 15'-5 | |
| Spruce Pine Fir | 2x4 | 6'-6 | 5'-11 | 5'-2 |
| 2x6 | 10'-3 | 9'-4 | 8'-1 | |
| 2x8 | 13'-1 | 12'-2 | 10'-8 | |
| 2x10 | 15'-1 | 14'-1 | 13'-1 | |
| 2x12 | 16'-11 | 15'-9 | 14'-8 | |
Maximum Spans for Ceiling Joists
Attics not Accessible by a Stairway
Span in feet-inches using #2 and better
| Species | Dimension | Spacing of Joists with Strapping and Bridging | ||
|---|---|---|---|---|
| 12" | 16" | 24" | ||
| Hemlock Fir | 2x4 | 10'-8 | 9'-9 | 8'-6 |
| 2x6 | 16'-1 | 15'-4 | 13'-4 | |
| 2x8 | 22'-2 | 20'-1 | 17'-7 | |
| 2x10 | 28'-3 | 25'-8 | 22'-5 | |
| 2x12 | 34'-5 | 31'-3 | 27'-4 | |
| Spruce Pine Fir | 2x4 | 10'-2 | 9'-3 | 8'-1 |
| 2x6 | 16'-1 | 14'-7 | 12'-9 | |
| 2x8 | 21'-1 | 19'-2 | 16'-9 | |
| 2x10 | 26'-11 | 24'-6 | 21'-4 | |
| 2x12 | 32'-9 | 29'-10 | 26'-0 | |
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