2021 IRC Section R602
Wood wall framing is the skeleton of almost every house GCHS touches, whether that means reviewing plans for new infill construction or opening a wall during a rehab to move a doorway. Section R602 sets the rules for stud grade and spacing, how much a stud can be cut or drilled for plumbing and wiring before it stops doing its job, how top plates tie the walls together, and where fireblocking has to interrupt hidden cavities so a wall does not act like a chimney in a fire. A framing defect missed here is invisible again the moment drywall goes up.
Every stud, plate, and header in the wall has to be identified by the grade mark of an accredited grading agency (or an agency certificate of inspection), because the span, height, and spacing tables in this chapter are built on design values for a specific species and grade. Ungraded lumber cannot be checked against any of those tables, so an inspector has no basis to approve it no matter how sound it looks. Table R602.3(5) ties stud size and spacing to what the wall carries: a 2x4 bearing stud may be spaced 24 inches on center where it supports only a roof and ceiling, but only 16 inches where it also supports a floor, and no 2x4 is listed for two floors plus a roof. A wall with studs at 24 inches on center actually carrying two floors and a roof has no listed stud size that qualifies, so it has to be checked against the stud table for that loading condition; spacing alone does not tell you whether the wall is legal.
The single most important classification an inspector makes in this chapter is whether a wall is a bearing wall: one that carries vertical load from a floor, roof, or ceiling above it, in addition to its own weight. That status is about the load path, not the wall's location or height, and it drives almost everything else in this lesson: how deep a stud may be notched or bored, what a header needs, and what happens when a wall is removed. On a rehab job, cutting a doorway into what looks like an ordinary partition is safe only after that load path has actually been traced; a bearing wall needs a header, jack studs, and a verified path of support down to the foundation before the opening is cut.
Plumbing and electrical trades cut into studs constantly, and the code sets hard limits on how much wood can be removed before the stud is compromised. In an exterior wall or a bearing partition, a notch may remove no more than 25 percent of the stud's width, and a bored hole no more than 40 percent, though that hole limit rises to 60 percent where the studs are doubled, with no more than two successive doubled studs cut that deeply. Any bored hole must keep at least 5/8 inch of wood to the edge of the stud, and a hole may never land in the same cross-section as a notch; stacking the two cuts leaves a section far weaker than either limit alone assumes. Non-bearing partitions carry only their own weight and the wall finish, so the code relaxes the limits there to 40 percent for a notch and 60 percent for a bored hole.
A bearing wall normally gets a double top plate, and the two plates are staggered on purpose: end joints in the upper plate must be offset at least 24 inches from any joint in the plate below, so the assembly never breaks at the same point twice. At corners and wall intersections the plates lap over one another, turning the top of the framing into a continuous ring tying the building together against wind and seismic forces. A single top plate is allowed only where the framing above lands within about an inch of directly over the studs, with the missing tension continuity restored by approved connectors at corners, intersecting walls, and splices in straight runs (Table R602.3.2 lists steel splice plates for this), since without the second plate there is nothing left to distribute load sideways between studs.
Sometimes a plate has to be cut for a duct chase or a beam pocket. Where the cut removes more than half the width of a double top plate and that side of the wall is not fully sheathed with wood structural panel, the code requires a galvanized steel tie, not less than 0.054 inch thick and 1-1/2 inches wide, fastened across the opening at each side with not less than eight 10d nails at least 1-1/2 inches long, and the tie must extend at least 6 inches past the opening. That strap does the job the continuous plate used to do; skip it and the tension ring has a gap exactly where a duct crosses the wall.
A cripple wall is the short wall between the top of the foundation and the underside of the first floor framing, and it carries everything the wall above it carries, so the code never allows it to be framed lighter than the studs above; once it exceeds 4 feet in height it is treated like a story of its own and sized accordingly. Where an exterior cripple wall's studs run shorter than 14 inches, the code requires the wall to be continuously sheathed on one side with wood structural panel fastened to both top and bottom plates, or built as solid blocking, rather than left as a row of short, unbraced studs. Cripple walls also have to sit on a continuous foundation.
Where a sill or bottom plate sits on a concrete slab in direct contact with the ground, it has to be naturally durable wood or preservative-treated wood unless an impervious moisture barrier separates it from the slab, and wood framing resting directly on an exterior foundation wall less than 8 inches above exposed ground has to be durable or treated as well (R317.1). Concrete wicks ground moisture continuously, and an untreated plate there becomes a permanently damp decay site running the length of the wall.
Fireblocking is the material that seals off the hidden pathways inside a wall so a fire cannot travel through the framing faster than it travels through the occupied space. In concealed stud wall spaces it is required vertically at the ceiling and floor levels, closing off the cavity where it would otherwise open into the attic or floor system above and below, and horizontally at intervals not exceeding 10 feet, a rule that matters most in long balloon-framed or furred walls. The code accepts solid lumber at least 2 inches nominal, two layers of 1-inch nominal lumber with staggered joints, 23/32-inch wood structural panel with backed joints, 1/2-inch gypsum board, or certain mineral wool or glass fiber batts; ordinary plastic sheeting is not on that list, because it melts away in the first moments of a fire instead of holding the opening closed.
Fireblocking also belongs at every other place a concealed cavity connects to another concealed space: at the top and bottom of stair stringers, where a plumbing vent pierces a top plate into the attic, and at the interconnection between a soffit or dropped ceiling and the vertical stud cavities behind it. Around a masonry chimney passing through a floor, the material has to be noncombustible, since fireblocking there sees sustained heat that would defeat ordinary wood or gypsum blocking. An uninterrupted balloon-framed wall running from foundation to attic is one continuous flue, and retrofitting fireblocking at each floor level is a standard finding when that framing gets exposed during a rehab.
In the field
On an older Gulf Coast rehab, opening a kitchen wall for new cabinetry often exposes a soffit built decades ago that ties straight into the open stud cavity below it, with no blocking at the connection. It looks harmless with nothing burning, but that open path is exactly the shortcut a kitchen fire would take from the wall into the ceiling plenum and across the house. GCHS treats this as a standard fireblocking correction whenever a soffit or dropped-ceiling space is opened up, since the framing inspection is the only real chance to confirm it before the drywall goes back.
A plumber needs to run a 1-1/2-inch supply line through a 2x4 stud in a bearing wall. A 2x4 stud is 3-1/2 inches wide, and the bearing-wall bored hole limit is 40 percent of that width: 3.5 in. × 0.40 = 1.4 inches. A 1-1/2-inch hole exceeds that by a tenth of an inch, so the cut is not allowed in a single 2x4 there; the fallback is doubling the stud, which raises the limit to 60 percent (3.5 in. × 0.60 = 2.1 inches), comfortably clearing the pipe. Checking the math against the actual pipe size, rather than eyeballing the hole, is what catches a shortfall like this before the wall is closed up.
1. End joints in a double top plate of a bearing wall must be offset from joints in the plate below by at least:
2. In a bearing wall, a notch in a stud may be no deeper than what percentage of the stud's width?
3. A bored hole in any stud must be at least how far from the edge of the stud?
4. Fireblocking is required in concealed stud wall spaces horizontally at intervals not exceeding:
5. A plumber bores a hole through studs in a bearing wall equal to 55% of the stud width. This is permitted only if:
6. In a NON-bearing interior partition, a stud may be notched to a maximum of:
7. A duct chase requires cutting the double top plate of a bearing wall more than 50 percent of its width, and the wall is not fully sheathed on that side. The required repair is:
8. A single top plate is used on a bearing wall. It is acceptable only if:
9. An exterior cripple wall between the foundation and the first floor has a stud height of 11 inches. The code requires it to be:
10. Cripple wall studs must be:
11. A stud in a bearing wall has both a 1-inch bored hole and a 3/4-inch notch at the same height. The inspector should:
12. A 3-inch drain must be concealed in a bearing wall, so the wall is framed with 2x6 studs instead of 2x4s. The framing reason is:
13. An inspector finds a dropped soffit above kitchen cabinets that connects to the open stud cavities of the wall behind. The correct call is:
14. A homeowner has cut a large pass-through opening in an interior wall without a permit. The inspector's FIRST determination should be: