Corner boards are commonly used with white cedar shingles, but in traditional style, shingles or shakes are joined to each other at the corners.
Outside corners. With shakes and red-cedar shingles, corners are often woven with two courses on one side alternating with two courses on the other, each hand-planed to the corner profile. This is labor-intensive; small, galvanized finish nails are recommended to hold the butt joints closed.
Mitering shingles is not recommended. These corners are likely to open when the siding shrinks, even if the miters are pinned.
Inside corners. Flash inside corners with a right-angle flashing extended at least 3 in. under the shingle courses. At a minimum, all inside corners should receive an extra layer of building paper.
The simplest inside corner trim is a 1x1 or 2x2 wood strip installed in the corner with the shingles butted against it. Inside corners also may be woven in a manner similar to outside corners.