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Rafter span tables - Use these tables to determine lengths, sizes and spacing of rafters based on a variety of factors such as, species, load, grade, spacing and pitch. Visit the roof framing page for more information on cutting roof rafters, and visit the roof pitch calculator for determining rafter lengths based on rise and run.
For example, in the rafter span table below, the highlighted cell (in the 40# Live Load table), indicates that 2" x 8" Southern Yellow Pine joists, that have a grade of #2, that are spaced 24" apart, can have a maximum span of 10 feet - 3 inches (10-3) if designing for a live load of 40 lbs/ft2.
Use these two tables for roof rafters with a slope of 3" in 12" or less.
| Nominal Size | Spacing (o.c.) | Species and Grade of Lumber ( 20# Live Load - No Finished Ceiling) | |||
| Southern Yellow Pine | Southern Yellow Pine | Douglas Fir | Eastern Spruce | ||
| #1 grade (kiln dried) | #2 grade | #2 grade | Structural | ||
| 2" x 6" | 12 | 16-5 | 14-2 | 15-4 | 14-4 |
| 16 | 14-8 | 12-4 | 13-3 | 12-10 | |
| 24 | 12-8 | 10-0 | 10-10 | 10-5 | |
| 2" x 8" | 12 | 21-7 | 18-9 | 20-3 | 19-4 |
| 16 | 19-6 | 16-3 | 17-6 | 16-10 | |
| 24 | 16-8 | 13-3 | 14-4 | 13-9 | |
| 2" x 10" | 12 | 27-6 | 23-11 | 25-10 | 24-6 |
| 16 | 24-8 | 20-8 | 22-4 | 21-6 | |
| 24 | 21-3 | 16-11 | 18-3 | 17-7 | |
| 2" x 12" | 12 | 33-5 | 29-1 | 31-4 | 30-0 |
| 16 | 30-0 | 25-2 | 27-2 | 26-2 | |
| 24 | 25-10 | 20-6 | 22-2 | 21-5 | |
| Nominal Size | Spacing (o.c.) | Species and Grade of Lumber ( 40# Live Load - No Finished Ceiling) | |||
| Southern Yellow Pine | Southern Yellow Pine | Douglas Fir | Eastern Spruce | ||
| #1 grade (kiln dried) | #2 grade | #2 grade | Structural | ||
| 2" x 6" | 12 | 13-0 | 11-0 | 11-11 | 11-5 |
| 16 | 11-9 | 9-6 | 10-3 | 9-11 | |
| 24 | 9-9 | 7-9 | 8-5 | 8-1 | |
| 2" x 8" | 12 | 17-2 | 14-6 | 15-8 | 15-1 |
| 16 | 15-6 | 12-7 | 13-7 | 13-1 | |
| 24 | 12-11 | 10-3 | 11-1 | 10-8 | |
| 2" x 10" | 12 | 21-10 | 18-6 | 20-0 | 19-3 |
| 16 | 20-0 | 16-0 | 17-4 | 16-8 | |
| 24 | 16-6 | 13-1 | 14-2 | 13-7 | |
| 2" x 12" | 12 | 26-6 | 22-6 | 24-4 | 23-5 |
| 16 | 24-4 | 19-6 | 21-1 | 20-3 | |
| 24 | 20-0 | 15-11 | 17-2 | 16-7 | |
Use these two tables for roof rafters with a slope greater than 3" in 12".
| Nominal Size | Spacing (o.c.) | Species and Grade of Lumber ( 20# Live Load - Light Roofing) | |||
| Southern Yellow Pine | Southern Yellow Pine | Douglas Fir | Eastern Spruce | ||
| #1 grade (kiln dried) | #2 grade | #2 grade | Structural | ||
| 2" x 4" | 12 | 11-6 | 10-3 | 11-0 | 9-11 |
| 16 | 10-5 | 9-1 | 9-6 | 8-7 | |
| 24 | 8-6 | 7-4 | 7-9 | 7-0 | |
| 2" x 6" | 12 | 18-1 | 15-0 | 16-2 | 15-7 |
| 16 | 16-4 | 13-0 | 14-0 | 13-6 | |
| 24 | 13-4 | 10-7 | 11-5 | 11-0 | |
| 2" x 8" | 12 | 23-8 | 19-9 | 21-4 | 20-6 |
| 16 | 21-6 | 17-1 | 18-5 | 17-9 | |
| 24 | 17-7 | 13-11 | 15-1 | 14-6 | |
| 2" x 10" | 12 | 30-3 | 25-2 | 27-2 | 26-2 |
| 16 | 27-5 | 21-10 | 23-7 | 22-8 | |
| 24 | 22-5 | 17-10 | 19-3 | 18-6 | |
| Nominal Size | Spacing (o.c.) | Species and Grade of Lumber ( 40# Live Load - Heavy Roofing) | |||
| Southern Yellow Pine | Southern Yellow Pine | Douglas Fir | Eastern Spruce | ||
| #1 grade (kiln dried) | #2 grade | #2 grade | Structural | ||
| 2" x 4" | 12 | 8-5 | 7-4 | 7-8 | 6-11 |
| 16 | 7-3 | 6-4 | 6-8 | 6-0 | |
| 24 | 5-11 | 5-2 | 5-5 | 4-11 | |
| 2" x 6" | 12 | 13-2 | 10-6 | 11-4 | 10-11 |
| 16 | 11-5 | 9-1 | 9-10 | 9-5 | |
| 24 | 9-4 | 7-5 | 8-0 | 7-9 | |
| 2" x 8" | 12 | 17-5 | 13-10 | 14-11 | 14-5 |
| 16 | 15-1 | 12-0 | 12-11 | 12-6 | |
| 24 | 12-4 | 9-9 | 10-7 | 10-2 | |
| 2" x 10" | 12 | 22-2 | 17-8 | 19-1 | 18-4 |
| 16 | 19-3 | 15-3 | 16-6 | 15-11 | |
| 24 | 15-8 | 12-6 | 13-6 | 13-0 | |
The above spans are based on American Softwood Lumber standard sizes.
** Note: The data in the rafter span tables above were obtained from Architectural Drawing and Light Construction by Edward J. Muller.
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