What is the minimum plywood thickness for a shear wall?
IRC R602 sets 3/8 inch as the absolute minimum, but the practical minimum in real US construction is 15/32 inch (11.9 mm). Most engineering schedules call for 15/32" APA-rated Sheathing or 19/32" APA-rated Structural I depending on the shear load. The structural engineer's schedule on the permit drawings is the authoritative spec.
Is OSB acceptable for shear walls under code?
Yes. IBC 2306 and the APA design guides allow OSB and plywood with equivalent code capacities at the same edge-nailing schedule. The two materials differ in fastener pullout, moisture behavior, and edge-nail splitting risk, but for routine residential walls in dry climates they are functionally interchangeable. Plywood is the safer call when the sheathing will sit weathered before cladding goes on.
Why are holdowns required at shear wall corners?
Holdowns transfer the overturning load from the lateral force on the wall into the foundation. Without them, the sheathing takes the in-plane shear but the wall pulls out of the foundation at one corner. The engineer's schedule specifies the holdown type (Simpson HTT, PHD, STHD families), anchor bolt size, and embedment depth. Sheathing capacity and holdown capacity must both be present for the wall to perform as designed.
Can Vietnamese film-faced formwork plywood be used as US shear-wall sheathing?
No. Film-faced formwork plywood (Pro Form, HDO range) is engineered for concrete-forming reuse — the spec target is film durability and core glue weather resistance, not in-plane shear for a code-rated wall. The panels are not APA span-rated, the film face is not the right surface for the nail-set required by the code schedule, and the layup is not optimized for in-plane shear. US shear walls require APA-rated Sheathing or Structural I from domestic mills.
