According to Chris Hunt and his co-authors on Installation, Care, and Maintenance of Wood Shake and Shingle Siding, shakes or shingles can be applied directly over properly installed and flashed Type 30 felt (or house wrap as approved by local codes). Shakes and shingles may be single-coursed,
The double-course application permits the use of a lower grade for the first layer and a greater exposure of the higher quality second layer of shake or shingle. Pressure-impregnated preservative-treated products can be used in these applications.
So the homeowner who wants the beauty and natural look of cedar siding can use these techniques to cover existing siding.