How a wall is framed

Behind the drywall of almost every American house is the same skeleton: a row of vertical studs standing on a horizontal plate and capped by another. The pattern is so regular that once you know it, you can find a stud with a knuckle and a tape measure, know where a header hides above a window, and understand why some walls can come out and others cannot.

The parts

Sole plate (bottom plate). The horizontal board the studs stand on. Code requires studs to have full bearing on a nominal 2-by or larger plate at least as wide as the studs.

Studs. The Wood Handbook’s definition: one of a series of slender wood structural members used as supporting elements in walls and partitions. Code requires them to be continuous from the sole plate to the top plate to resist loads perpendicular to the wall. Exterior wall studs in one- and two-story houses are at least nominal 2x4s, and the American Wood Council’s framing details put them at 16 inches on center, with 24-inch spacing of 2x4s also acceptable; the residential code’s stud table sets the maximum by stud size, wall height and whether the wall is bearing. Sixteen inches on center means the center of every stud is 16 inches from the next, which is why drywall and sheathing come in 48-inch widths.

Double top plate. Wood stud walls are capped with a double top plate installed to provide overlapping at corners and at intersections with bearing partitions, with the end joints in the two layers offset at least 24 inches. The overlap ties the walls into a continuous ring.

Header. Over every window and door opening, a header of adequate size is required to carry vertical loads across the opening. Its depth depends on the span and the load above.

King studs and jack studs. The full-length stud on each side of a door or window opening is the king stud. Nailed to it on the inside is the jack stud (also called a trimmer), cut to length to fit under each end of the header and down to the bottom plate; the jacks transfer the load the header carries down to the bottom plate.

Cripple studs. Short studs installed where a common stud would have been: below window openings from the rough sill to the bottom plate, and above headers up to the top plate.

Fire blocking. Inside the wall, fire blocking cuts off concealed draft openings, vertical and horizontal, to form an effective fire barrier between stories. In stud walls it is required at the ceiling and floor levels and horizontally at intervals not exceeding 10 feet. It is the reason a wall cavity is not a chimney.

Over the outside of the studs goes sheathing, plywood or OSB, which braces the wall against racking; over the inside goes drywall.

Load-bearing or not

The code definition of a load-bearing wall: a wall supporting any vertical load in addition to its own weight. A non-bearing wall carries only itself, and code allows it to be built lighter, for instance with 2x3 studs at 24 inches on center for interior non-bearing walls.

From the room you often cannot tell which is which. A wall running perpendicular to the floor joists above it, a wall stacked over a beam or another wall below, a wall with a deep header over its doorway, a wall in the middle of a wide house: each is a hint toward bearing, but none is proof. The Home Depot’s guide to the subject lists the stakes: most areas require building permits to remove load-bearing walls; a replacement beam must be sized, and consulting a structural engineer is the way to do it; and before removing a load-bearing wall you must build a temporary wall or bracing to support the joists while the work is done.

What you can cut, and how much

Running a pipe or a cable through a wall means drilling or notching studs, and the code limits how much. Under the model residential code (your local edition may differ, so check before cutting), any stud in an exterior wall or bearing partition may be notched to no more than 25 percent of its width. A bored hole may be up to 60 percent of the stud width, but it must stay at least 5/8 inch from the stud’s edge, it cannot share a section with a notch, and in an exterior or bearing wall any hole over 40 percent means the stud has to be doubled, with no more than two doubled studs in a row bored. Go past those and the stud stops being a stud.

Finding a stud

The regular spacing is the trick. Measure from a corner, an outlet (boxes are nailed to the side of a stud) or a door casing (the king stud is right behind it) in 16-inch steps, and confirm with a stud finder or a small finish nail where the baseboard will hide the hole. Studs on both sides of a window are doubled, and there is always one at each corner.

When to call a pro

Hanging a shelf, a television mount or a cabinet on studs is homeowner work. Opening a wall to run a new circuit, cutting a new door or window opening, and removing or shortening any wall that might be bearing are permit-and-professional work: a structural engineer to size the header or beam, a licensed contractor to build the temporary support and the new structure, and an inspector to sign it off. The cost of guessing wrong is the floor above.

Related

• Almanac: September, acclimating wood for fall projects
• How wood moves with the seasons, How a door hangs and why it sticks
• Glossary: stud, sole plate, top plate, header, king stud, jack stud, cripple stud, fire blocking, joist