Framing Rough Openings: Headers, Kings & Jacks

📐 Rough Opening Sizes: The +2" Rule and Its Exceptions

The rough opening is measured between the inside faces of the jack studs (width) and from the subfloor — or top of the rough sill — to the underside of the header (height).

• Prehung doors: slab width + 2 inches, slab height + 2 to 2½ inches. The extra 2 inches absorbs two ¾-inch jambs plus shim space. A 36×80 door frames at 38 × 82–82½ inches, which is why the standard header height lands at 82½ inches above subfloor.
• Windows: use the manufacturer's R.O. table, period. The generic rule (unit + ½ inch each side) is only a placeholder — real tolerances vary from ⅜ to ¾ inch per side by brand and series, and flanged units differ from block-frame. Frame from the window schedule, not from the glass size.
• Standard interior slabs run 24, 28, 30, 32, and 36 inches wide × 80 tall — so the most common R.O. you'll ever frame is 32 × 82½ (for a 30-inch door) or 38 × 82½ (for a 36).

🪵 Sizing the Header: How the IRC Tables Actually Work

Headers in bearing walls are sized from IRC Table R602.7(1) (exterior) or R602.7(2) (interior). Four inputs drive the lookup:

1. What the wall supports — roof + ceiling only, plus one floor, plus two floors (and whether floors are center-bearing or clear-span).
2. Ground snow load — tabulated at 30 and 50 psf, interpolation allowed between.
3. Building width — 12, 24, or 36 ft perpendicular to the ridge (interpolate between).
4. Header span — which equals the rough-opening width. The tabulated span is the clear distance between jack-stud faces. A classic estimating error is subtracting jack thickness from the R.O. before entering the table; don't.

For scale, with No. 2 SPF/DF-L at 30 psf snow on a 24-ft-wide building supporting roof and ceiling: a double 2×6 header carries roughly a 5½–6 ft opening on one jack per side, and a double 2×10 reaches about 9–9½ ft on two jacks. Stack a floor on top and the same 2×10 drops to around 7 ft. The tables reward checking rather than guessing — and the framing calculator runs the lookup for you.

• Southern Pine caveat: the IRC header tables are valid for No. 2 Douglas Fir-Larch, Hem-Fir, and SPF — but No. 2 Southern Pine design values were revised down in 2013, so SP headers use the AWC WFCM supplemental tables instead.
• 2×6 walls and the sandwich header: two plies plus rigid foam fills the wall depth and insulates the header. The foam is non-structural, so the plies are drawn together with structural screws (5-inch+ SDWS/HeadLOK class), not nails through foam.
• When to leave the tables: spans beyond the largest table entry, point loads landing on the header (a beam or post from above — the tables assume distributed load only), or walls over 10 ft. That's LVL/LSL territory, sized from manufacturer tables, and worth a design professional's stamp.

Non-bearing walls skip all of this: IRC R602.7 allows a single flat 2×4 as the "header" for openings up to 8 ft in a non-bearing wall (when the top plate or parallel nailing surface is within 24 inches above). No jacks, no cripples required. Confirming which walls actually bear load is therefore the first question of any remodel opening.

🦴 Kings, Jacks, and Cripples: Who Does What

• NJ and kings are separate counts. The header table's NJ column is jacks only; kings come from Table R602.7.5 on top of that. Conflating them under-frames wide openings.
• The king-to-header connection is specified: 4-16d nails end-nailed through each king into each end of the header (IRC R602.7.5). Where NJ = 1, code lets an approved framing anchor replace the jack — useful when you need every inch of opening width.
• Window openings get cripples twice: above the header (if dropped) and always below the rough sill. Forgetting the sill cripples is the most common stud-count omission — every one of them is a nailing surface the drywall crew expects to find.
• Total width between kings = R.O. + 3 inches per jack pair side (1½ inches per jack) — what you actually lay out on the plates.

🔨 The Layout Sequence That Avoids Rework

1. Confirm bearing vs. non-bearing. It changes everything above — and guessing wrong in a remodel is a structural problem, not a framing style choice. When in doubt, treat it as bearing or get an engineer's read.
2. Get the real R.O. numbers — door schedule math (+2") and manufacturer window tables — before cutting a single plate.
3. Size the header from the table using the R.O. as the span; keep it tight to the top plate if the wall height allows, for the full rated span and fewer cripples.
4. Lay out kings and jacks on the plates (R.O. + jack allowances), keeping the wall's common studs on their 16"/24" layout right through the opening — cripples land on layout.
5. Nail per schedule: jacks to kings face-nailed, kings to header 4-16d each end, header plies face-nailed per the built-up header row of the fastener table.

Openings are also where material estimates quietly go wrong: each one adds kings, jacks, and cripples that a bare length-÷-spacing count misses. The Framing Calculator counts them per opening, and the board foot calculator converts the lumber list for the yard. Related structure math lives on the Framing & Structure hub — and if the opening is for a new window in a bedroom, check the egress numbers in our permits & code guide before you frame it.