At inside corners, siding is frequently butted against a trim strip. It can also be butted against adjoining walls with a trim strip used to cover the join. At outside corners, some builders choose mitered corners for a professional looking finish. Mitered corners are most common on horizontally applied siding and they must fit tightly for the full depth of the miter. To maintain a tight fit, the siding should be properly seasoned before installation and protected from the weather at the job site. The ends are often set in caulking compound when siding is applied.

Corner boards are a popular alternative to mitered corners. They are often 3/4 in. or 1-1/4 in. material depending on the thickness of the siding. Width is a matter of taste and proper proportion. Corner boards are applied to the sheathing with the siding fitting tightly against the narrow edge of the boards. Joints should be filled with caulking compound when siding is applied. Trim boards can be used to cover butt jointed siding.

The corner boards and the ends of the siding are nailed to the corner studs which anchors the wood for a maintenance-free joint. Designing roofs with an eaves overhang to protect corners from weathering also helps ensure trouble-free joints.

When butt jointing siding, cut ends at 45 degree angles to form an overlapping joint. This is particularly important for vertical installation.