Maximum span by grade
| Grade | Maximum span |
|---|---|
| Select Structural | 16′-4″ |
| No. 1 | 15′-9″ |
| No. 2 | 15′-0″ |
| No. 3 | 11′-6″ |
Span tables · Ceiling joists · 20 psf
20 psf live · L/240
2x6 Douglas Fir-Larch ceiling joist span at 12″ o.c.
At 12″ o.c., a 2x6 Douglas Fir-Larch #2 ceiling joist spans up to 15′-0″ under this table's load case. Select Structural and No. 1 reach further; No. 3 less. See the full grade breakdown below.
Douglas Fir-Larch #2, 20 psf
What this span means
This is the maximum clear span the Table R802.5.1(2) permits for a 2x6 Douglas Fir-Larch ceiling joist spaced 12″ o.c., carrying 20 psf of live load plus 10 psf dead load with a L/240 deflection limit. A blank cell means the span exceeds the maximum shown in the source table for that size.
Actual allowable spans depend on your real loads, the lumber's moisture and exact grade stamp, bearing and connection details, and any point loads or openings. Treat this as a starting point, then confirm the member with your local code and a design professional.
The figure above is a clear span between the faces of the supports, not the length of the board - how to read a span table covers that and the other misreadings worth checking before you cut. For what the L/240 limit in this table's heading is doing to the number, see what L/360 deflection means; for what the 12″ o.c. spacing costs, 16 in vs 24 in on center.
Source: International Residential Code (IRC), 2018 - Table R802.5.1(2) - Ceiling Joist Spans, 20 psf Live Load (limited attic storage). Published by International Code Council.
Edition: These values are transcribed from the IRC 2018 tables. The ICC has since published IRC 2021 and IRC 2024, and the edition in force varies by jurisdiction - confirm the table and edition adopted by your local building department before relying on a span.
Frequently asked questions
How far can a 2x6 Douglas Fir-Larch ceiling joist span at 12″ o.c.?
A No. 2 2x6 Douglas Fir-Larch ceiling joist spaced 12″ o.c. spans up to 15′-0″ under 20 psf live load plus 10 psf dead load, with deflection limited to L/240. That figure is the clear span between the faces of the supports, not the length of the board. Source: International Residential Code (IRC), 2018 - Table R802.5.1(2) - Ceiling Joist Spans, 20 psf Live Load (limited attic storage) (International Code Council).
Does the lumber grade change how far a 2x6 Douglas Fir-Larch ceiling joist spans?
The table publishes a separate span per grade. At 12″ o.c., a 2x6 Douglas Fir-Larch ceiling joist spans Select Structural 16′-4″, No. 1 15′-9″, No. 2 15′-0″ and No. 3 11′-6″. Douglas Fir-Larch is the species group the table was published for and the grade is the stamp on the board, so both have to match the lumber you actually buy. A blank cell means the span exceeds the maximum shown in the source table for that size.
What is the span for a 2x6 Douglas Fir-Larch ceiling joist at other on-center spacings?
The source table publishes a separate span for every on-center spacing, and the span never gets longer as the spacing widens. For a No. 2 2x6 Douglas Fir-Larch ceiling joist under this load case: 12″ o.c. 15′-0″, 16″ o.c. 13′-0″, 19.2″ o.c. 11′-11″ and 24″ o.c. 10′-8″. This page reports the 12″ o.c. row.
What load case does this 2x6 Douglas Fir-Larch ceiling joist span assume?
Ceiling Joists - 20 psf Live Load (Limited Attic Storage): 20 psf live load plus 10 psf dead load, with deflection limited to L/240. Ceiling joists for attics with limited storage. Covers Douglas Fir-Larch and Hem-Fir per the published source table. Source: International Residential Code (IRC), 2018 - Table R802.5.1(2) - Ceiling Joist Spans, 20 psf Live Load (limited attic storage) (International Code Council).
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