Maximum span by grade
| Grade | Maximum span |
|---|---|
| Select Structural | 13′-4″ |
| No. 1 | 12′-10″ |
| No. 2 | 11′-10″ |
| No. 3 | 8′-11″ |
Span tables · Floor joists · 40 psf
40 psf live · L/360
2x8 Southern Pine floor joist span at 16″ o.c.
At 16″ o.c., a 2x8 Southern Pine #2 floor joist spans up to 11′-10″ under this table's load case. Select Structural and No. 1 reach further; No. 3 less. See the full grade breakdown below.
Southern Pine #2, 40 psf
What this span means
This is the maximum clear span the Table R502.3.1(2) permits for a 2x8 Southern Pine floor joist spaced 16″ o.c., carrying 40 psf of live load plus 10 psf dead load with a L/360 deflection limit. Spans are for repetitive members (three or more). Southern Pine values reflect the SPIB design values referenced by the IRC.
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/360 limit in this table's heading is doing to the number, see what L/360 deflection means; for what the 16″ o.c. spacing costs, 16 in vs 24 in on center.
Same member, other load case: Floor joists · 30 psf.
Source: International Residential Code (IRC), 2018 - Table R502.3.1(2) - Floor Joist Spans, 40 psf Live Load. 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 2x8 Southern Pine floor joist span at 16″ o.c.?
A No. 2 2x8 Southern Pine floor joist spaced 16″ o.c. spans up to 11′-10″ under 40 psf live load plus 10 psf dead load, with deflection limited to L/360. 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 R502.3.1(2) - Floor Joist Spans, 40 psf Live Load (International Code Council).
Does the lumber grade change how far a 2x8 Southern Pine floor joist spans?
The table publishes a separate span per grade. At 16″ o.c., a 2x8 Southern Pine floor joist spans Select Structural 13′-4″, No. 1 12′-10″, No. 2 11′-10″ and No. 3 8′-11″. Southern Pine 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. Spans are for repetitive members (three or more). Southern Pine values reflect the SPIB design values referenced by the IRC.
What is the span for a 2x8 Southern Pine floor 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 2x8 Southern Pine floor joist under this load case: 12″ o.c. 13′-6″, 16″ o.c. 11′-10″, 19.2″ o.c. 10′-10″ and 24″ o.c. 9′-8″. This page reports the 16″ o.c. row.
What load case does this 2x8 Southern Pine floor joist span assume?
Floor Joists - 40 psf Live Load (Living Areas): 40 psf live load plus 10 psf dead load, with deflection limited to L/360. Living rooms, kitchens, halls and other non-sleeping floor areas. The same member and spacing under the other published load case is covered by Floor Joists - 30 psf Live Load (Sleeping Areas). Source: International Residential Code (IRC), 2018 - Table R502.3.1(2) - Floor Joist Spans, 40 psf Live Load (International Code Council).
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