2021 IRC Sections R702-R703
This lesson moves from the wall's structure to its skin, inside and out. Anchored brick veneer and cast-in-place concrete are two very different wall types with one thing in common: once the work is covered up, almost nothing about it can be verified again, so the inspection has to happen at the right moment during construction. Interior gypsum board and exterior siding, stucco, and water-resistive barriers get the same treatment here: a handful of numbers that show up on almost every rehab and infill job GCHS reviews.
Brick veneer over a wood-framed wall is a reservoir cladding: it absorbs rain and releases it, including inward toward the sheathing, so the assembly depends on a working drainage system rather than on the brick being watertight. Anchored veneer over a wood or steel backing is limited to the first story above grade and 5 inches in thickness, with taller heights allowed only under the code's veneer tables (R703.8). That system starts with an air space of at least 1 inch nominal between veneer and sheathing, giving water a path down and a capillary break so moisture in the brick cannot bridge to the sheathing. Water-resistive barrier goes against the sheathing behind that space, and base flashing sits at the bottom of the air space, turned up the backup wall behind the barrier so the barrier laps over it, catching everything that runs down the cavity. Weep holes, at least 3/16 inch in diameter and spaced no more than 33 inches on center, sit immediately above that flashing so the collected water can exit. Mortar droppings that pile up on the flashing can dam that water instead; the code tolerates some mortar in an air space that still drains, but a choked cavity does not, which is why cavity cleanliness is an inspection item.
Ties and vertical support do two different jobs on a veneer wall, and confusing them leads to details that look complete but do not work. Corrosion-resistant wall ties, fastened to the framing and embedded in a mortar bed joint, resist the lateral, in-and-out wind and seismic force on the veneer; they carry essentially no vertical load. The brick's actual weight has to land on a noncombustible foundation, a ledge, or an approved lintel or shelf angle carrying it to the structure (in Seismic Design Categories A through C, veneer up to 40 pounds per square foot may also be carried by wood or cold-formed steel construction designed for it), because ties alone will not hold up a wythe of brick indefinitely. A masonry lintel spanning an opening needs at least 4 inches of bearing at each end so it can deliver its reaction into the surrounding masonry without crushing the units at the opening's edge, and because masonry is brittle and cracks under very small movement, the wood or cold-formed steel construction that supports veneer is limited to a deflection of 1/600 of the span, which is tighter than for an ordinary framing member (R703.8.2).
Getting a wall's water management right is almost entirely about sequencing: every layer has to shed onto the layer below it, like shingles, down to the weeps. R703.4 requires corrosion-resistant flashing, applied shingle-fashion, anywhere the drainage plane is interrupted or a horizontal surface can collect water: window and door openings, the intersection of chimneys or other masonry with frame or stucco walls, under and at the ends of copings and sills, above projecting wood trim, where porches, decks, or stairs attach to the wall, at wall and roof intersections, and at built-in gutters. At a window opening the flashing follows the window manufacturer's instructions; where none are given, the code calls for a pan flashing at the sill with flashing or protection at the head and sides. The usual order is sill pan first, then the window, then jamb flashing, then head flashing tucked behind the WRB above it; taping the head flashing on top of the wrap instead creates a shelf that channels water into the wall. A sill pan turns the rough sill into a small roof with end dams, so anything past the window's corners drains back out instead of soaking the framing. Where a roof slope dies into a sidewall, the wall and roof intersection needs flashing, and a kickout flashing is the usual detail that throws that runoff clear of the cladding and into the gutter; skip it and that corner becomes a reliable source of hidden wall rot.
Three-coat cement plaster over wire lath on an exterior wall must finish at least 7/8 inch thick, measured from the face of the backing, across its scratch, brown, and finish coats (Table R702.1(1); expanded metal lath has its own rule of 5/8 inch measured from the face of the lath). Self-furring lath is used over solid substrates to hold the lath off the surface so the scratch coat can fully embed and key behind it; flat lath has nothing to key into and the finish delaminates in sheets. Control joints accommodate the shrinkage and thermal movement plaster inevitably undergoes, deciding where the resulting crack goes. A weep screed goes at or below the foundation plate line, at least 4 inches above earth or 2 inches above paved areas, so water behind the stucco can drain out. Over wood-based sheathing, a single ordinary layer of WRB is not enough behind stucco, since wet plaster pulls water through it; the assembly needs an enhanced system, such as two layers of 10-minute Grade D paper, giving a sacrificial bond layer plus an intact drainage layer, and in moist or marine zones, including the Gulf Coast, an added drainage space or material at least 3/16 inch deep on the exterior side of the barrier. EIFS over a wood-framed wall has to be an EIFS with drainage (R703.9.2): at least 90 percent average drainage efficiency when tested, with the water-resistive barrier between the EIFS and the sheathing, ending at least 6 inches above the ground. Plain face-sealed EIFS is limited to concrete or masonry substrates, because on wood framing it produced widespread hidden wall rot historically when water had no way out.
Behind any exterior wall covering, the WRB's main job is to provide a drainage plane carrying incidental water past the siding back out, not to act as the primary weather surface. As No. 15 asphalt felt, it laps shingle-style, upper courses over lower, with horizontal laps of at least 2 inches and vertical joints lapped at least 6 inches; a reverse lap anywhere is a classic field failure. The barrier has to run continuous to the top of the wall and terminate properly at penetrations, and manufacturers add taping and sealing details for seams and penetrations, since open seams and reverse laps let wind-driven rain reach the sheathing. Siding fasteners over wood sheathing are generally driven into the studs, not just the sheathing, unless the manufacturer or the code's optional attachment table allows otherwise, because wind pressure acts outward as often as inward, and a nail held only by sheathing can pull through. Vinyl siding is installed per the manufacturer's instructions (R703.11.1), with nails left slightly loose and centered in the slot so the panel can expand and contract; nailing tight shows up later as a wavy, buckled wall.
Gypsum board fastening is keyed to whether the board goes on a wall or a ceiling, because gravity pulls a ceiling board off its framing in a way it does not pull on a wall board. For 1/2-inch gypsum board fastened without adhesive to walls framed at 16 inches on center, the maximum spacing is 8 inches for nails and 16 inches for screws; on ceilings that tightens to 7 inches for nails and 12 inches for screws. A drywall screw in wood framing must penetrate the framing member at least 5/8 inch to develop real withdrawal resistance; a screw that only catches the surface lets the board pop loose as the framing dries and moves. Around tubs and showers, ordinary paper-faced water-resistant board, including green board, is not acceptable directly behind tile in the wetted area; that location needs a backer from the code's list (Table R702.4.2), such as cementitious, fiber-cement, glass-mat gypsum, or fiber-reinforced gypsum, and the wall above a tub with a showerhead needs a nonabsorbent finish extending at least 6 feet above the floor, since spray and condensation below that line are constant and an absorbent finish there will fail and feed mold behind the tile.
Concrete wall thickness and reinforcement for a dwelling come from the code's tables (R404.1.2 for basement walls) keyed to the wall's height, the unbalanced backfill height against it, and the lateral load the soil applies, or from an engineered design where the tables do not cover the condition. Changing the backfill height on site without rechecking the table is a real and recurring problem on rehab projects built into a slope. Because the forms on an insulating concrete form (ICF) wall never come off, the critical inspection window is entirely before the pour: rebar size, spacing, cover, bracing, and form alignment all have to be verified then, since none of it can be checked again once the concrete has set. A cold joint, formed when a pour is interrupted too long and fresh concrete never bonds to the hardened concrete beside it, is both a structural discontinuity in shear transfer and a potential water path, and depending on location may need an approved treatment or waterstop rather than being treated as cosmetic.
In the field
A common finding on older Gulf Coast homes is a brick veneer wall with no visible weep holes along the base course. Before writing that up, check whether the veneer's flashing line is even visible, or whether it has been buried below grade or behind a later patio poured up against the brick. A buried weep is itself the real defect, since it cannot drain anything, but the correction differs from a wall built without weeps in the first place, so establishing where the flashing line sits comes before deciding what to cite.
A 32-foot brick veneer wall is being detailed for a rehab addition. At the code minimum of 33 inches on center for weep spacing, the wall needs at least 32 ft × 12 in./ft ÷ 33 in. = 11.6, so 12 weep holes minimum, each at least 3/16 inch in diameter, set immediately above the base flashing. Behind the brick, the air space must be at least 1 inch nominal (and, with standard W1.7 adjustable ties, no more than 4-5/8 inches from backing to veneer), and it has to stay open enough to drain, since a pinched section anywhere along the cavity can dam water exactly where the wall cannot afford it.
1. Anchored brick veneer requires weep holes spaced no more than:
2. Behind exterior siding, the water-resistive barrier must be installed:
3. Cement plaster (stucco) applied over wire lath on an exterior wood-framed wall has a minimum finished thickness, measured from the face of the backing, of:
4. For 1/2-inch gypsum board fastened (without adhesive) to WALLS framed at 16 inches on center, the maximum fastener spacing is:
5. A drywall screw in wood framing must penetrate the framing member by at least:
6. Which backing material is NOT permitted directly behind tile in a shower wall's directly wetted area?
7. Wall surfaces above a bathtub with a showerhead must have a nonabsorbent finish extending to a height of at least:
8. A masonry lintel over a window opening must have a bearing length at each end of at least:
9. Anchored masonry veneer over wood framing must be supported by:
10. The air space between anchored brick veneer and the sheathing must be at least:
11. Flashing at a window opening in a wall with housewrap must be applied shingle-fashion. The correct sequence is to:
12. Wood siding must be kept a minimum distance from exposed earth of:
13. Cast-in-place concrete wall thickness and reinforcement for a dwelling are determined by:
14. An inspector examining a brick veneer wall notices no visible weeps anywhere along the base course. Before writing the violation, the FIRST thing to verify is: