A jack stud, also called a trimmer stud, is a vertical framing member positioned just inside the king stud at a rough opening, running from the bottom plate up to the underside of the header, directly supporting the header’s weight rather than the full wall height a king stud spans.
This shorter length is intentional, since the jack stud’s specific job is to catch the header’s load right where the opening begins, transferring it down to the bottom plate and foundation below.
The number of jack studs required scales with the opening’s width and the load the header carries, meaning wider openings often need multiple jack studs stacked together for adequate support.
What Does a Jack Stud Involve?
- Lumber cut to the height beneath the header
- Placement directly against the king stud
- Direct support for the header above
- Multiple studs together for wider or more heavily loaded openings
Why Are Jack Studs Important?
As the direct support beneath a header, jack studs bear significant concentrated load, especially under wide openings or load-bearing walls, making their sizing and quantity a genuine structural calculation rather than a matter of convention alone. Undersized or too few jack studs beneath a heavily loaded header is a real, if sometimes overlooked, structural deficiency that inspectors specifically check for during framing inspections.
On particularly wide openings, like a large sliding door or a wall largely opened up during a remodel, an engineer’s calculation for the exact number of required jack studs is often necessary rather than relying on standard rule-of-thumb framing practices alone.
Jack Stud vs. King Stud
A jack stud directly supports the header, running only up to the underside of that beam. A king stud runs the full wall height alongside it, tying the opening into the wall’s broader structural system and providing the outer support the jack stud rests against.