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Rafter Span Tables

Maximum allowable rafter spans per IRC for residential roof construction. 20 psf live load (roof snow/wind), 10 psf dead load. L/180 deflection limit.

Rafter calculator →Roof area calculator →

Douglas Fir-Larch — #1

Rafter Size12" o.c.16" o.c.24" o.c.
2x616'-6"15'-0"13'-0"
2x821'-9"19'-9"17'-2"
2x1027'-9"24'-6"20'-0"
2x1233'-9"29'-3"23'-11"

Douglas Fir-Larch — #2

Rafter Size12" o.c.16" o.c.24" o.c.
2x615'-10"14'-5"12'-5"
2x820'-11"19'-0"16'-4"
2x1026'-8"23'-3"19'-0"
2x1232'-5"27'-6"22'-5"

Southern Pine — #1

Rafter Size12" o.c.16" o.c.24" o.c.
2x616'-6"15'-0"13'-0"
2x821'-9"19'-9"17'-2"
2x1027'-9"24'-6"20'-0"
2x1233'-9"29'-3"23'-11"

Southern Pine — #2

Rafter Size12" o.c.16" o.c.24" o.c.
2x615'-4"13'-11"11'-6"
2x820'-3"18'-4"15'-0"
2x1025'-10"22'-6"18'-4"
2x1231'-5"26'-4"21'-6"

Hem-Fir — #1

Rafter Size12" o.c.16" o.c.24" o.c.
2x615'-7"14'-2"12'-4"
2x820'-7"18'-8"16'-3"
2x1026'-3"23'-3"19'-0"
2x1231'-11"27'-9"22'-8"

Spruce-Pine-Fir — #1/#2

Rafter Size12" o.c.16" o.c.24" o.c.
2x615'-0"13'-7"11'-10"
2x819'-9"17'-11"15'-7"
2x1025'-2"22'-3"18'-2"
2x1230'-7"26'-7"21'-8"

Understanding Rafter Spans

Rafter span is the horizontal distance from the bearing point at the wall plate to the bearing point at the ridge or the opposite wall. It is NOT the rafter length along the slope — the actual rafter you need to cut is longer than the span.

Use the rafter calculator to convert from span and pitch to actual cutting length, including overhang.

Rafter Span vs. Joist Span

Rafter spans are generally longer than floor joist spans for the same lumber size because roof loads (20 psf live) are lighter than floor loads (40 psf live). A 2x10 rafter at 16" o.c. can span about 24 feet, while a 2x10 floor joist at 16" o.c. only spans about 19 feet.

Related Resources

Span values are simplified from IRC rafter span tables for common residential loading. Always verify with your local building code. Not a substitute for professional engineering judgment.