Certigrade #4 Undercourse Shingles are a utility grade for undercoursing of double coursed sidewalls only. Cedar undercourse shingles can be used for creating interior decor that has rustic appeal with the warmth of real wood. With unlimited defects, flat grain and sapwood, these shingles are not intended to be used as siding. Wood undercourse can be an economical option for shims, or other utility functions.