2×8 floor joist spans (2021 IRC)
Every allowable span the 2021 International Residential Code floor tables list for a 2×8 joist — four species, four grades, four spacings, both load cases — each table cited where it sits.
2021 IRC Table R502.3.1(2) covers residential living areas; 2021 IRC Table R502.3.1(1) covers residential sleeping areas. Both tables are below, in that order.
A 2×8 Southern pine No. 2 floor joist at 16-inch centers spans up to 11’10” under standard residential living-area loads (2021 IRC Table R502.3.1(2)). Widen the spacing to 24-inch centers and the same joist is listed at 9’8”; hold 16-inch centers and switch to Spruce-pine-fir No. 2 and the table lists 12’3”. Under 2021 IRC Table R502.3.1(1) — residential sleeping areas, 30 psf live / 10 psf dead / L/360 — that same Southern pine No. 2 at 16 inches is listed at 13’3”.
2×8 floor joists — residential living areas
| 2×8 — species and grade | 12" on center | 16" on center | 19.2" on center | 24" on center |
|---|---|---|---|---|
| Douglas fir-larch Select Structural | 15’0” | 13’7” | 12’10” | 11’11” |
| Douglas fir-larch No. 1 | 14’5” | 13’1” | 12’4” | 11’0” |
| Douglas fir-larch No. 2 | 14’2” | 12’9” | 11’8” | 10’5” |
| Douglas fir-larch No. 3 | 11’3” | 9’9” | 8’11” | 8’0” |
| Hem-fir Select Structural | 14’2” | 12’10” | 12’1” | 11’3” |
| Hem-fir No. 1 | 13’10” | 12’7” | 11’10” | 10’10” |
| Hem-fir No. 2 | 13’2” | 12’0” | 11’3” | 10’2” |
| Hem-fir No. 3 | 11’0” | 9’6” | 8’8” | 7’9” |
| Southern pine Select Structural | 14’8” | 13’4” | 12’7” | 11’8” |
| Southern pine No. 1 | 14’2” | 12’10” | 12’1” | 11’3” |
| Southern pine No. 2 | 13’6” | 11’10” | 10’10” | 9’8” |
| Southern pine No. 3 | 10’3” | 8’11” | 8’2” | 7’3” |
| Spruce-pine-fir Select Structural | 13’10” | 12’7” | 11’10” | 11’0” |
| Spruce-pine-fir No. 1 | 13’6” | 12’3” | 11’6” | 10’3” |
| Spruce-pine-fir No. 2 | 13’6” | 12’3” | 11’6” | 10’3” |
| Spruce-pine-fir No. 3 | 11’0” | 9’6” | 8’8” | 7’9” |
2021 IRC Table R502.3.1(2) — residential living areas, 40 psf live / 10 psf dead / L/360. table source
2×8 floor joists — residential sleeping areas
| 2×8 — species and grade | 12" on center | 16" on center | 19.2" on center | 24" on center |
|---|---|---|---|---|
| Douglas fir-larch Select Structural | 16’6” | 15’0” | 14’1” | 13’1” |
| Douglas fir-larch No. 1 | 15’10” | 14’5” | 13’7” | 12’4” |
| Douglas fir-larch No. 2 | 15’7” | 14’2” | 13’0” | 11’8” |
| Douglas fir-larch No. 3 | 12’7” | 10’11” | 10’0” | 8’11” |
| Hem-fir Select Structural | 15’7” | 14’2” | 13’4” | 12’4” |
| Hem-fir No. 1 | 15’3” | 13’10” | 13’0” | 12’1” |
| Hem-fir No. 2 | 14’6” | 13’2” | 12’5” | 11’4” |
| Hem-fir No. 3 | 12’4” | 10’8” | 9’9” | 8’8” |
| Southern pine Select Structural | 16’2” | 14’8” | 13’10” | 12’10” |
| Southern pine No. 1 | 15’7” | 14’2” | 13’4” | 12’4” |
| Southern pine No. 2 | 14’11” | 13’3” | 12’1” | 10’10” |
| Southern pine No. 3 | 11’6” | 10’0” | 9’1” | 8’2” |
| Spruce-pine-fir Select Structural | 15’3” | 13’10” | 13’0” | 12’1” |
| Spruce-pine-fir No. 1 | 14’11” | 13’6” | 12’9” | 11’6” |
| Spruce-pine-fir No. 2 | 14’11” | 13’6” | 12’9” | 11’6” |
| Spruce-pine-fir No. 3 | 12’4” | 10’8” | 9’9” | 8’8” |
2021 IRC Table R502.3.1(1) — residential sleeping areas, 30 psf live / 10 psf dead / L/360. table source
What these tables state
Each number is the span the code table lists for that species, grade, and on-center spacing at the load case stamped at the top of this page: 40 psf live / 10 psf dead / L/360 for residential living areas, 30 psf live / 10 psf dead / L/360 for residential sleeping areas. Change the spacing, the grade, or the species and you are reading a different cell of the same table.
Point loads, cantilevers beyond the table footnotes, unusual snow loads, or anything else outside the table's stated conditions — that's an engineer's question.
Other sizes and assemblies
Other floor joist sizes: 2×6 floor joists · 2×10 floor joists · 2×12 floor joists
The same 2×8 in other assemblies: 2×8 ceiling joists · 2×8 rafters · 2×8 deck joists
Common questions
Can 2×8 floor joists span 14 feet?
At 16-inch centers, 2×8 Southern pine No. 2 is listed at 11’10” in 2021 IRC Table R502.3.1(2) (40 psf live / 10 psf dead / L/360). 6 of the 64 2×8 cells in that table are 14 feet or longer, and the widest spacing among them is 12-inch centers — Douglas fir-larch No. 2 at 12 inches is listed at 14’2”.
How far can a 2×8 floor joist span at 24-inch centers?
2021 IRC Table R502.3.1(2) — residential living areas — lists 2×8 No. 2 at 24-inch centers as Douglas fir-larch 10’5”, Hem-fir 10’2”, Southern pine 9’8”, Spruce-pine-fir 10’3”. The same four species in 2021 IRC Table R502.3.1(1) (residential sleeping areas): 11’8”, 11’4”, 10’10”, 11’6”.
What is the difference between the two 2021 IRC floor joist tables for a 2×8?
2021 IRC Table R502.3.1(1) covers residential sleeping areas at 30 psf live / 10 psf dead / L/360; 2021 IRC Table R502.3.1(2) covers residential living areas at 40 psf live / 10 psf dead / L/360. Same 2×8 Southern pine No. 2 at 16-inch centers: 13’3” in the first, 11’10” in the second.