What grades of redwood lumber must be grade stamped?
Foundation grade and Deck grades are special purpose grades which must be grade stamped.

Foundation grade is selected from two-inch or thicker Construction Heart or better for durability and ability to resist insect and fungus attacks. This grade is typically used for mud sills as an alternative to pressure-treated wood.

Deck Heart and Deck Common are two grades of redwood especially suited for residential or non-residential exterior patio deck uses where specific design values are required in combination with an attractive appearance. These grades are manufactured in 2-inch thickness, in 4- and 6-inch widths. The characteristics and limiting provisions for these grades are essentially the same as those for General Purpose Grades of Construction Heart and Construction Common. The primary difference is the inclusion of slope of grain requirements and knot measurement based upon equivalent displacement rather than average diameter.