How to Install Corners on Lap Siding

Lap siding installers often install corner pieces instead instead of attempting to miter each strip of siding.

Lap siding corners can transition from one siding material to another.Lap siding corners can transition from one siding material to another.
Corner pieces provide a solid water-tight and professional-looking edge that the lap siding slats butt against. Mitered corners leak, and look unprofessional, unless each of the siding's slats have the correct miter angle and the slat's layout lines up perfectly on each wall. Lap siding corner boards hide minor differences and imperfections in the slat's layout. Installing lap siding corner boards reduces labor cost and time when compared to mitering each siding slat.

Measure the length of the corner with a tape measure. The measurement must extend from the bottom of the wall to the point where the corner meets the soffit. Measure each corner separately.

Transfer the corner's length measurement to the lap siding corner boards. Inside corners use a single square board. Outside corners need two boards; one board's width measurement exceeds the other board's width measurement by the thickness of the corner board. Use a pencil and a carpenter's square to draw a right-angled line across the boards' width at the length measurement.

Cut the lap siding's corner boards along the pencil lines with a saw. Any saw with a wood-cutting blade will work, but most siding installers use either a circular saw or a chop saw.

Tack an inside corner board to the wall's sheathing with a 6D nail. Hold the corner board 1/8 inch below the soffit and tight to both pieces of sheathing. Drive the first nail through the corner board 2 inches from the top with a hammer, then drive a nail every 18 inches. Place the last nail 2 inches from the bottom.

Tack the lap siding's narrow outside corner board to the wall's sheathing with a 6D nail. Hold the narrow board so its top edge rests 1/8 inch below the soffit and its butt edge -- the edge that the wide board butts up to -- sits flush with the sheathing's corner. Drive the first nail in the center of the board 2 inches from the top. Drive a nail every 18 inches and place the last nail 2 inches from the bottom of the corner board.

Run a 1/8-inch wide bead of exterior grade caulk over the butt end of the lap siding's narrow corner board. Keep the bead near the edge of the board that touches the sheathing.

Hold the lap siding's wide corner board against the wall's sheathing with the corner board's top edge 1/8 inch below the soffit and its outside edge -- the edge that laps over the narrow board -- flush with the outside of the narrow board. Tack the wide corner board in place with a 6D nail placed 2 inches from the top and in the center of the board. Drive a nail every 18 inches and place the last nail 2 inches from the bottom.

Wipe any excess caulk from the lap siding's corner boards with a rag. Do not allow the caulk to dry.

Things You Will Need

  • Tape measure
  • Pencil
  • Carpenter square
  • Saw with wood-cutting blade
  • 6D nails
  • Hammer
  • Exterior-grade caulk
  • Rag

About the Author

Based out of Central Florida, Robert Sylvus has been writing how-to and outdoor sports articles for various online publications since 2008. Sylvus has been a home improvement contractor since 1992. He is a certified HVAC universal technician.