From the following plywood grades, which would NOT normally be used for sheathing or underlayment?

• A. A-C.
• B. A-A
• C. B-C
• D. C-D

Answer: (A)

Plywood grades tell you surface quality on each side, and for sheathing or underlayment you want a panel where the faces are suitable for fasteners, nail holding, and a stable, predictable surface. A panel that has a premium, smooth face on one side but a noticeably lower-quality back on the other isn’t the typical choice for these uses because the back’s defects can still affect performance and you don’t gain a practical finish benefit from that side. In practice, sheathing or underlayment panels come in combinations where both faces are reasonably balanced (or where exterior-grade bonding is specified), such as options that pairing mid-to-low or matching grades and exterior adhesive, ensuring consistent strength and handling. Therefore, the pairing where one face is top-quality and the other is significantly lower quality is not normally used for sheathing or underlayment.