A 6 ft opening in an exterior wall of a house 24 ft wide, carrying only the roof and ceiling under a 30 psf ground snow load, needs a 2-2×10 header: two 2×10s, good for up to 6 ft 10 in, with 2 jack studs and 2 king studs at each end. That comes straight from IRC Table R602.7(1). Put a floor on that wall, or raise the snow load to 50 psf, and the same opening needs a 2-2×12.
How the beam span is found
The IRC header and girder tables list the longest span each built-up header may cover, for No. 2 Douglas fir-larch, hem-fir, Southern pine and spruce-pine-fir, so the species does not change the answer. The span depends on three things:
- What the wall carries: roof and ceiling only, or also one or two floors, and whether those floors are center-bearing (supported in the middle) or clear-span.
- Building width, measured across the ridge. The tables list 12, 24 and 36 ft, and footnote c allows interpolating between them.
- Ground snow load for exterior walls: 30, 50 or 70 psf. Use 30 where the snow load is less and the roof live load is 20 psf or less (footnote e).
Span at your width = span at the lower width + (span at the upper width − span at the lower width) × (your width − lower width) ÷ 12 ft.
For a 28 ft house the 2-2×10 in the roof and ceiling case spans 82 in at 24 ft and 69 in at 36 ft: 82 + (69 − 82) × 4 ÷ 12 = 77.7 in, or 6 ft 5 ¹¹⁄₁₆ in. The 6 ft opening still fits under it.
The calculator then takes the shallowest header with the number of plies your wall wants (two 2× plies and a ½ in plywood spacer make a 3½ in header for a 2×4 wall, three plies suit a 2×6 wall) whose span covers the opening.
Header span chart: exterior wall, roof and ceiling, 30 psf
From IRC Table R602.7(1). The number in brackets is the jack studs needed at each end.
| Header | 12 ft wide | 24 ft wide | 36 ft wide |
|---|---|---|---|
| 2-2×4 | 4 ft 0 in (1) | 3 ft 1 in (1) | 2 ft 7 in (1) |
| 2-2×6 | 6 ft 0 in (1) | 4 ft 7 in (1) | 3 ft 10 in (1) |
| 2-2×8 | 7 ft 7 in (1) | 5 ft 9 in (1) | 4 ft 10 in (2) |
| 2-2×10 | 9 ft 0 in (1) | 6 ft 10 in (2) | 5 ft 9 in (2) |
| 2-2×12 | 10 ft 7 in (2) | 8 ft 1 in (2) | 6 ft 10 in (2) |
| 3-2×12 | 13 ft 2 in (1) | 10 ft 1 in (2) | 8 ft 6 in (2) |
| 4-2×12 | 15 ft 3 in (1) | 11 ft 8 in (1) | 9 ft 10 in (2) |
The interactive table under the calculator shows every size for the case you pick, with the spans that cover your opening in dark type.
Interior bearing walls and porch beams
Interior bearing walls use Table R602.7(2), which has no snow load: the header carries one floor or two. In a 24 ft house, one floor over a 2-2×10 allows 6 ft 6 in with 2 jacks at each end.
Open porch beams use Table R602.7(3), by porch depth (8 or 14 ft, interpolated between) and whether the beam carries the porch roof or a floor. An 8 ft deep porch roof at 30 psf lets a 2-2×10 span 12 ft 4 in and a 2-2×8 10 ft 1 in; at 10 ft deep the 2-2×10 drops to 11 ft 4 in. Posts carry these beams, so no jack studs are listed.
Jack studs and king studs
The NJ column of each table gives the jack studs at each end; where it says 1, footnote d allows an approved framing anchor in place of the jack. Beside the jacks, IRC Table R602.7.5 sets the full-height king studs for exterior walls: up to 140 mph design wind speed, 1 for a header up to 4 ft, 2 up to 8 ft, 3 up to 14 ft and 4 up to 18 ft. The 6 ft header in the example gets 2.
When the top of the header is not braced
The spans assume floor or roof framing braces the top of the header sideways. If cripple studs bear on the header instead, footnote f of Table R602.7(1) multiplies the spans of 2×8, 2×10 and 2×12 headers by 0.70. The 2-2×10 in the example drops from 6 ft 10 in to 4 ft 9⅜ in, too short for 6 ft.
When the tables stop
The tables end at a 36 ft building width and 70 psf ground snow, and they do not cover point loads from a post above, ridge beams, or engineered lumber. LVL, PSL and glulam beams are sized from each manufacturer's own span tables. Anything the tables do not cover needs a design, and a new opening in a bearing wall needs temporary support while you cut it.
Related calculators
- Count every header, jack and king for a whole set of walls with the framing calculator, or one wall stud by stud with the stud calculator.
- Joists under a deck: the deck joist span calculator. Roof framing: the rafter calculator.
- Price the header lumber with the lumber calculator.