Joist Span Tables - Ceiling Joists

Ceiling Joist Spans for Common Species of Lumber

Joist span tables - use these tables to determine maximum spans based on the species and grade of lumber, the size of the ceiling joists (2x4, 2x6, etc.), and the spacing of the ceiling joists. The ceiling joist tables below cover the following two design scenarios:

Uninhabitable attics without storage, a live load of 10 Psf, a dead load of 5 Psf, and a deflection limit of L/240.
Uninhabitable attics with limited storage, a live load of 20 Psf, a dead load of 10 Psf, and a deflection limit of L/240.

Note: Ceiling joists on the first floor of a two-story structure that also serves as floor joists for the second floor should use the Floor Joist Span Table to determine the maximum joist length.

Ceiling Joist Spans

Example: The highlighted cell (below) shows that a 2" x 6" Douglas Fir joist, with a grade of #2, spaced 24" apart, can have a maximum span of 10 feet - 8 inches (10-8). Based on the following design requirements: an uninhabitable attic with limited storage has a live load of 20 Psf, a dead load of 10 Psf, and a deflection limit of L/240 (span in inches divided by 240).

Ceiling Joist Span Tables

Uninhabitable attics without storage, a live load of 10 Psf, a dead load of 5 Psf, and a deflection limit of L/240

Nominal Size	Spaced (o.c.)	Species/Grade
		S. Pine	Doug. Fir	Hem-fir	S.P.F.
		#2 grade	#2 grade	#2 grade	#2 grade
2" x 4"	12	11-10	12-5	11-7	11-10
	16	10-9	11-3	10-6	10-9
	24	9-3	9-10	9-2	9-5
2" x 6"	12	18-8	19-6	18-2	18-8
	16	16-11	17-8	16-6	16-11
	24	13-11	15-0	14-5	14-9
2" x 8"	12	24-7	25-8	24-0	24-7
	16	21-7	23-4	21-9	22-4
	24	17-7	19-1	18-6	18-9
2" x 10"	12	**	**	**	**
	16	25-7	**	**	**
	24	20-11	23-3	22-7	22-11

** Span is greater than 26 feet in length.

Uninhabitable attics with limited storage, a live load of 20 Psf, a dead load of 10 Psf, and a deflection limit of L/240

Nominal Size	Spaced (o.c.)	Species/Grade
		S. Pine	Doug. Fir	Hem-fir	S.P.F.
		#2 grade	#2 grade	#2 grade	#2 grade
2" x 4"	12	9-3	9-10	9-2	9-5
	16	8-0	8-11	8-4	8-7
	24	6-7	7-3	7-1	7-2
2" x 6"	12	13-11	15-0	14-5	14-9
	16	12-0	13-0	12-8	12-10
	24	9-10	10-8	10-4	10-6
2" x 8"	12	17-7	19-1	18-6	22-11
	16	15-3	16-6	16-0	16-3
	24	12-6	13-6	13-1	13-3
2" x 10"	12	20-11	23-3	22-7	22-11
	16	18-1	20-2	19-7	19-10
	24	14-9	16-5	16-0	16-3

The above spans are from the American Softwood Lumber standard sizes.

To calculate maximum joist spans using different design criteria (loading, spacing, grade, etc.) for these common lumber species, see the International Residential Code (IRC).

To calculate the maximum spans of species not shown above, use the Span Calculator or the Span Tables for Joists and Rafters on the American Wood Council website.