Plywood Grades and Exposure Ratings

Plywood is graded by its veneer (on the front and back panels) and its exposure rating.

Veneer Grade   Characteristics
N   Smooth natural finish select heartwood or sapwood veneer, free of open defects. This grade does not allow more than six wood-only repairs per 4 ft. x 8 ft. panel. Grain and color must be well matched.
A   Smooth paint-grade veneer; may be used natural for less demanding applications. No more than 18 repairs per 4 ft. x 8 ft. panel.
B   Solid surface veneer. This grade allows tight knots (no more than 1 inch. in diameter), round repair plugs and shims. Permits repairs of minor splits.
C-Plugged   Upgraded "C" veneer. Splits limited to 1/8 inch max. width. No knotholes or borer holes permitted larger than 1/4 x 1/2 inch. Synthetic repairs permitted, as well as some limited broken grain.
C   This veneer can have tight knots up to 1 1/2 inches in diameter, and knotholes up to 1 inch across the grain, or up to 1 1/2 inches if the total width of knots and knotholes is within specified limits. Wood and/or synthetic repairs allowed. Discoloration and sanding defects which to not impair strength are allowed.
D   D grade allows knots and knotholes up to 2 1/2 inches width across the grain as well as limited splits and stitches, and is limited to interior or Exposure 1 panels.

Exposure Ratings
Exterior   Fully waterproof bond. Designed for applications where panels are subject to permanent ongoing exposure to moisture.
Exterior - Exposure 1   Fully waterproof bond, but not intended for permanent ongoing exposure to moisture.
Exterior - Exposure 2   Interior type with intermediate glue. Intended for protected applications where only slight exposure to moisture is likely to occur.
Interior2   Designed for interior applications only.