How to Finish the Corners on 4x8 Siding

Sheet siding is almost always installed vertically.
Sheet siding is almost always installed vertically. (Image: New house under construction waiting for the landscaping. image by Tom Oliveira from

Of the many types of siding you can choose for your house, 4x8 sheets are probably the easiest to apply. The most common are T1-11, a type of plywood that usually has a rough-sawn surface, and oriented stand board (OSB), an inferior product made of wood fibers and resin pressed together. It is almost always preferable to install sheet siding vertically. The sheets do not have to form a seal at the corners of the house. You create the seal after the siding is up by trimming the corners with wooden trim boards.

Things You'll Need

  • Tar paper or house wrap
  • Staple gun
  • 8d galvanized nails
  • 1- by 4-inch lumber
  • Circular saw
  • Siliconized acrylic caulk
  • Caulking gun

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Cover the framing with tar paper or house wrap before you install the siding. Lay the material horizontally on the studs, starting at the bottom of the wall and overlapping each successive layer over the one below it. Extend the tar paper or house wrap around the corners, rather than making a joint there. Staple it to the studs with a staple gun.

Install the sheets of siding vertically, starting at one end a wall and working towards the other. Bring the edges of the end sheets to within 1/2 inch of the end of each wall. It is not essential that they be exactly flush with the outside edges of the corner studs.

Nail the edges of the sheets securely to the corner studs with 8d galvanized nails. Drive the nails at 8- to 10-inch intervals.

Cut two lengths of 1- by 4-inch lumber to extend from the soffit to the bottom edge of the siding for each corner with a circular saw.

Nail one length of corner trim to one side of a corner so that the outside edge is flush with the surface of the siding on the other side of the corner. Drive the 8d nails near the outside edge of the trim to be sure they sink into the stud underneath the siding.

Nail the other length of corner trim to the other side of the corner so that the outside edge is flush with surface of the first trim board you installed. The two trim boards should fit tightly together where they overlap.

Lay a bead of siliconized acrylic caulk along the edges of both corner trim boards where they meet the siding. It usually isn't necessary to lay caulk in the gap between the two trim boards, as long as they fit tightly.

Tips & Warnings

  • If your siding has vertical grooves, try to avoid having the edge of either trim board lay over a groove, or it will be more difficult to seal the gap with caulk.


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