Do You Miter Corners with Exterior Siding?

Type of Siding

• Mitered corners are most common among solid wood siding products, such as solid board and batten siding and plank siding. Manufacturers of plywood and composite siding materials, such as fiber-cement or hardboard, typically recommend that installers cover corners with well-sealed trim pieces. The easiest types of solid wood siding to miter are planks that lie flat against the wall, such as tongue-and-groove or ship-lap siding, which require only 45-degree cuts to form tight corners.

Common Challenges

• Bevel and lap siding are horizontal siding planks that overlap and protrude from the wall at their bottom edges. Unlike flat planks, which meet at a 45-degree miter, these lapping planks meet at a compound angle, usually several degrees off 45 degrees. Creating mitered corners at compound angles requires attention to detail and good carpentry skills. Small mistakes leave large, unacceptable gaps at corners, effectively ruining the expensive siding planks. If you plan to miter bevel siding, practice on scrap pieces until you're confident of you skills, or choose an alternative corner construction method.

Nailing and Sealing Procedure

• Conventional exterior siding installation calls for a special nailing procedure at mitered corners. Along with nails that drive through the face of the siding into wall framing, drive one nail through the miter into the opposite board at each side. Finish nails or thin siding nails are the only nails that work without splitting the corner. If you properly cut and butt mitered siding, the result should be a tight seal that doesn't require gobs of sealant, caulk or adhesive. Professionals occasionally omit sealants altogether and simply use thick coats of paint to seal corners. If corners move with the structure's natural shifting, however, paint can crack and create an opening in the seals.

Alternatives

• Metal corners and corner boards are the most common alternatives to mitering. Among composite and plywood siding products, they are more common than mitering. Metal corners are basically lightweight, metal angles that slip over the corner between two planks. Corners are suitable for plank siding, particularly lap and bevel siding planks. Corner boards are essentially flat trim pieces that match the siding material. Builders fasten a corner board over each side of a wall's corner and typically apply sealant or caulk around the boards' perimeter. Corner boards may meet at a flat butt-joint or a miter joint.