A rafter span chart lists the maximum horizontal span for a rafter of a given size, species, grade, and spacing under a stated roof load. Under 2021 IRC Table R802.4.1(1) (20 psf roof live load, 10 psf dead load, ceiling not attached), a #2 Douglas fir-larch rafter at 16" o.c. spans 14'-7" as a 2x6, 18'-5" as a 2x8, and 22'-6" as a 2x10.
The charts below are copied from the 2021 International Residential Code. They are prescriptive limits for the load case printed in each caption only. Your jurisdiction's adopted code and local amendments govern, and trusses and engineered rafters use the manufacturer's design. For how rafters show up on the drawing, start with the roof framing plan guide.
How to read a rafter span table
Rafter tables have more inputs than floor tables. Every one of them has to match your roof:
- Species and grade. Douglas fir-larch, hem-fir, Southern pine, or spruce-pine-fir, in select structural, #1, #2, or #3. The charts here use #2. Read the grade stamp.
- Spacing. 12, 16, 19.2, or 24 inches on center. See floor joist spacing explained for what on-center means; it works the same way for rafters.
- Load. Tables R802.4.1(1) and (2) use a 20 psf roof live load. Tables R802.4.1(3) through (8) use ground snow loads instead.
- Dead load. Each table has a 10 psf and a 20 psf column. Dead load is the weight of the roof: rafters, sheathing, roofing, and anything else permanently on it. Heavier roofing moves you to the 20 psf column.
- Ceiling attached or not. This sets the deflection limit. L/Δ = 180 where no ceiling is attached to the rafters; L/Δ = 240 where one is.
- Ceiling joist or rafter tie height. Footnote a assumes the ties are at the bottom of the attic. Raised ties reduce the span (see below).
Rafter span is measured on the horizontal projection
Section R802.4.1 says rafter spans shall be measured along the horizontal projection of the rafter. In other words, measure the level distance in plan from the support at the wall to the support at the ridge. Do not measure the sloped length of the board. Pitch matters for ordering stock and cutting, which is covered in roof pitch and slope, but not for reading this table.
Rafter span chart: ceiling not attached (L/180)
Use this when the rafters carry roofing only and the ceiling below hangs from separate ceiling joists.
2021 IRC Table R802.4.1(1): #2 grade, roof live load 20 psf, dead load 10 psf, ceiling not attached to rafters, L/Δ = 180. Maximum rafter spans in feet-inches, horizontal projection. "Over 26'" is the table's note b, span exceeds 26 feet.
| Species and spacing | 2x4 | 2x6 | 2x8 | 2x10 | 2x12 |
|---|---|---|---|---|---|
| Douglas fir-larch @ 12" | 10'-10" | 16'-10" | 21'-4" | 26'-0" | Over 26' |
| Douglas fir-larch @ 16" | 9'-10" | 14'-7" | 18'-5" | 22'-6" | 26'-0" |
| Douglas fir-larch @ 19.2" | 9'-1" | 13'-3" | 16'-10" | 20'-7" | 23'-10" |
| Douglas fir-larch @ 24" | 8'-2" | 11'-11" | 15'-1" | 18'-5" | 21'-4" |
| Hem-fir @ 12" | 10'-1" | 15'-11" | 20'-8" | 25'-3" | Over 26' |
| Hem-fir @ 16" | 9'-2" | 14'-2" | 17'-11" | 21'-11" | 25'-5" |
| Hem-fir @ 19.2" | 8'-8" | 12'-11" | 16'-4" | 20'-0" | 23'-2" |
| Hem-fir @ 24" | 7'-11" | 11'-7" | 14'-8" | 17'-10" | 20'-9" |
| Southern pine @ 12" | 10'-4" | 15'-7" | 19'-8" | 23'-5" | Over 26' |
| Southern pine @ 16" | 9'-0" | 13'-6" | 17'-1" | 20'-3" | 23'-10" |
| Southern pine @ 19.2" | 8'-2" | 12'-3" | 15'-7" | 18'-6" | 21'-9" |
| Southern pine @ 24" | 7'-4" | 11'-0" | 13'-11" | 16'-6" | 19'-6" |
| Spruce-pine-fir @ 12" | 10'-4" | 16'-3" | 21'-0" | 25'-8" | Over 26' |
| Spruce-pine-fir @ 16" | 9'-5" | 14'-4" | 18'-2" | 22'-3" | 25'-9" |
| Spruce-pine-fir @ 19.2" | 8'-10" | 13'-1" | 16'-7" | 20'-3" | 23'-6" |
| Spruce-pine-fir @ 24" | 8'-0" | 11'-9" | 14'-10" | 18'-2" | 21'-0" |
Rafter span chart: ceiling attached (L/240)
Use this where a ceiling finish is fastened directly to the rafters, as in a vaulted ceiling.
2021 IRC Table R802.4.1(2): #2 grade, roof live load 20 psf, dead load 10 psf, ceiling attached to rafters, L/Δ = 240. Maximum rafter spans in feet-inches, horizontal projection. "Over 26'" is the table's note b.
| Species and spacing | 2x4 | 2x6 | 2x8 | 2x10 | 2x12 |
|---|---|---|---|---|---|
| Douglas fir-larch @ 12" | 9'-10" | 15'-6" | 20'-5" | 26'-0" | Over 26' |
| Douglas fir-larch @ 16" | 8'-11" | 14'-1" | 18'-5" | 22'-6" | 26'-0" |
| Douglas fir-larch @ 19.2" | 8'-5" | 13'-3" | 16'-10" | 20'-7" | 23'-10" |
| Douglas fir-larch @ 24" | 7'-10" | 11'-11" | 15'-1" | 18'-5" | 21'-4" |
| Hem-fir @ 12" | 9'-2" | 14'-5" | 19'-0" | 24'-3" | Over 26' |
| Hem-fir @ 16" | 8'-4" | 13'-1" | 17'-3" | 21'-11" | 25'-5" |
| Hem-fir @ 19.2" | 7'-10" | 12'-4" | 16'-3" | 20'-0" | 23'-2" |
| Hem-fir @ 24" | 7'-3" | 11'-5" | 14'-8" | 17'-10" | 20'-9" |
| Southern pine @ 12" | 9'-5" | 14'-9" | 19'-6" | 23'-5" | Over 26' |
| Southern pine @ 16" | 8'-7" | 13'-5" | 17'-1" | 20'-3" | 23'-10" |
| Southern pine @ 19.2" | 8'-1" | 12'-3" | 15'-7" | 18'-6" | 21'-9" |
| Southern pine @ 24" | 7'-4" | 11'-0" | 13'-11" | 16'-6" | 19'-6" |
| Spruce-pine-fir @ 12" | 9'-5" | 14'-9" | 19'-6" | 24'-10" | Over 26' |
| Spruce-pine-fir @ 16" | 8'-7" | 13'-5" | 17'-9" | 22'-3" | 25'-9" |
| Spruce-pine-fir @ 19.2" | 8'-1" | 12'-8" | 16'-7" | 20'-3" | 23'-6" |
| Spruce-pine-fir @ 24" | 7'-6" | 11'-9" | 14'-10" | 18'-2" | 21'-0" |
Comparing the two charts, the attached-ceiling limit cuts spans in the smaller sizes, where stiffness controls. In the deeper sizes many values are identical, because strength rather than deflection governs there.
How far can a 2x6 or 2x8 rafter span?
At 16" o.c., #2 grade, 20 psf roof live load and 10 psf dead load:
- 2x6, ceiling not attached: 14'-7" DF-L, 14'-4" SPF, 14'-2" hem-fir, 13'-6" Southern pine.
- 2x6, ceiling attached: 14'-1" DF-L, 13'-5" SPF, 13'-1" hem-fir, 13'-5" Southern pine.
- 2x8, ceiling not attached: 18'-5" DF-L, 18'-2" SPF, 17'-11" hem-fir, 17'-1" Southern pine.
- 2x8, ceiling attached: 18'-5" DF-L, 17'-9" SPF, 17'-3" hem-fir, 17'-1" Southern pine.
Remember these are horizontal spans. On a gable roof with a ridge board, each rafter's span is the plan distance from the wall support to the ridge support, roughly half the building width, not the full width.
Snow load rafter tables
If your area has a design ground snow load, the 20 psf live load charts above are not the ones to use. The 2021 IRC has six more rafter tables:
| Table | Ground snow load | Ceiling | Deflection |
|---|---|---|---|
| R802.4.1(3) | 30 psf | Not attached | L/180 |
| R802.4.1(4) | 30 psf | Attached | L/240 |
| R802.4.1(5) | 50 psf | Not attached | L/180 |
| R802.4.1(6) | 50 psf | Attached | L/240 |
| R802.4.1(7) | 70 psf | Not attached | L/180 |
| R802.4.1(8) | 70 psf | Attached | L/240 |
Spans drop as snow load rises. For example, a #2 Douglas fir-larch 2x8 at 16" o.c. with a 10 psf dead load spans 18'-5" in Table R802.4.1(1) but 15'-4" in Table R802.4.1(3) at 30 psf ground snow. Get the ground snow load for your site from the local building department before reading any rafter table.
When rafter ties sit higher in the attic
Footnote a to every rafter table assumes ceiling joists or rafter ties sit at the bottom of the attic, where they stop the rafters pushing the walls outward. Where the ties are higher, the spans are multiplied by the factors in Table R802.4.1(9), based on HC/HR (height of the ties above the wall plates divided by height of the ridge above the plates):
2021 IRC Table R802.4.1(9): rafter span adjustment factor.
| HC/HR | Adjustment factor |
|---|---|
| 1/3 | 0.67 |
| 1/4 | 0.76 |
| 1/5 | 0.83 |
| 1/6 | 0.90 |
| 1/7.5 or less | 1.00 |
Ties at one third of the attic height cut the allowed span by a third. Section R802.5.2 adds that where ceiling joists sit above the bottom third of the rafter height, the ridge must be designed as a beam. That is the dividing line covered in ridge beam vs ridge board.
Other rules around the span table
- Ridge board. Section R802.3 requires a ridge board at least 1 inch nominal thick and no less in depth than the cut end of the rafter.
- Low slopes. Under Section R802.4.4, where roof pitch is less than 3:12, ridges, hips, and valleys must be designed as beams.
- Purlins. Section R802.4.5 permits braced purlins to shorten a rafter's span, sized no smaller than the rafters they support.
- Other cases. For grades, species, or loads not in the tables, Section R802.4.1 points to the AWC Span Tables for Joists and Rafters, available through the American Wood Council span-table resources.
Ceiling joists have their own tables, covered in the ceiling joist span chart. Floor joists are in the floor joist span table, and the floor framing plan guide shows how those spans appear on a drawing. If you are deciding between stick framing and trusses, read rafters vs trusses first.
Showing rafters on a roof framing plan
A roof framing plan labels each rafter run with size, grade, and spacing, for example 2x8 #2 DF-L RAFTERS @ 16" O.C., plus the table and load case used. Framing Plan draws joist and member layouts, beams, and openings and exports PNG, PDF, and DXF, but it does not check rafter spans against the IRC: its bundled sample profile uses demo span figures and metric member sizes, and the editor authors in millimeters. Use the code tables for sizing and the app for the drawing. Open the framing studio to lay out a preliminary framing plan for review.