Door and window headers are the small built-up beams over framed openings. Get them too small and the wall sags into the opening; get them too big and you waste money and framing space. IRC R602.7 has a simplified table for typical residential cases — here is the plain-English version, with the disclaimers that have to come with it.
What a header carries
A header transfers load from above the opening — the floor, ceiling, or roof — sideways to the trimmer (jack) studs at either end of the opening, which then carry the load down to the foundation. The wider the opening, the heavier the load over it, and the bigger the header.
Three things determine the header size:
- Opening width. Rough opening, not finish opening.
- What is above the wall. Roof only, roof + 1 floor, or roof + 2 floors.
- Whether the wall is bearing. Non- bearing (parallel to joists) takes a token header; bearing walls take real headers.
Simplified IRC R602.7 quick-pick
For exterior bearing walls in a 28-ft-wide or smaller building, ground snow ≤ 30 psf, #2 SPF or better:
Roof + ceiling only (no floors above):
- Up to 3 ft → (2) 2x4
- Up to 5 ft → (2) 2x6
- Up to 7 ft → (2) 2x8
- Up to 8 ft → (2) 2x10
- Up to 10 ft → (3) 2x10
- Up to 12 ft → (3) 2x12
One floor + roof above:
- Up to 3 ft → (2) 2x6
- Up to 5 ft → (2) 2x8
- Up to 7 ft → (2) 2x10
- Up to 8 ft → (3) 2x10
- Up to 10 ft → (3) 2x12
- Beyond 10 ft → engineer-specified LVL
Two floors + roof above:
- Up to 3 ft → (2) 2x8
- Up to 5 ft → (2) 2x10
- Up to 7 ft → (3) 2x10
- Up to 8 ft → (3) 2x12
- Beyond 8 ft → engineer-specified LVL
Non-bearing (interior partition):
- Up to 4 ft → (2) 2x4
- Up to 8 ft → (2) 2x6
- Wider → (2) 2x8 minimum
The header size calculator walks the table for you and reports jack stud count too.
Building up the header
Two-ply headers sandwich a strip of 1/2" plywood (matching the wall stud width of 3-1/2") between the two 2x members, so the finished header is 3-1/2" wide and flush with the wall framing. Three-ply headers use two strips of 1/2" plywood. Nail the assembly together with 16d common at 12" o.c. staggered, top and bottom.
For 2x6 walls, you can stack two 2x members and use a flat 2x to fill the cripple space, or use engineered LVL sized to fit the wall depth.
Jack and king studs
The header bears on jack studs (also called trimmers) at each end. King studs run full height alongside each jack and tie the assembly into the wall above and below the opening. Quick rules:
- Up to 4 ft → 1 jack each side, 1 king each side
- 4 to 8 ft → 2 jacks each side, 1 king each side
- Over 8 ft → 3 jacks each side, 1 king each side; or engineered post + plate
When to skip the table and call an engineer
- Opening over 12 ft (or over 8 ft with two stories above)
- Heavy snow regions (ground snow over 50 psf)
- Buildings wider than 28 ft
- Garage door headers — almost always engineered LVL
- Anywhere a point load lands directly on the header
- Custom homes where the architect specs the header
LVL (laminated veneer lumber) handles the loads where built-up dimensional lumber runs out of capacity. A 1-3/4" x 9-1/4" LVL spans much farther than a (3) 2x10 in the same opening.
Common errors
Forgetting the plywood spacer. A built-up header without the 1/2" plywood between plies is only 3" wide and sits inside a 3-1/2" wall — drywall and trim pinch around it.
Crowning wrong.Each ply has a slight bow (the "crown"). Always orient all plies crown-up, so the header pre-stresses against the load instead of with it.
Not enough jacks. Bearing failure under a header almost always shows up as one jack stud splitting under the bottom plate. Wide openings need multiple jacks per side.
Quick FAQ
What size header for a 36-inch door? A (2) 2x6 with 1 jack and 1 king each side is plenty for a bearing or non-bearing wall. Many builders use (2) 2x8 or (2) 2x10 just to keep stock counts simple.
Can I use a single 2x as a header? Only on non-bearing walls under 4 ft, and even then most builders double-up out of habit. Bearing-wall headers are always built up.
When do I need an LVL? Anytime an opening exceeds the simplified table, two stories sit above a wide opening, or the engineer specs one. Garage door headers are almost always LVL.
Estimate only. The header size calculator uses a simplified read of IRC R602.7. Real header sizing depends on snow load, building width, lumber grade, and stacked loads. Verify with a licensed structural engineer or your building inspector before framing.