Increasing the height of an existing wood fence not only adds decorative detail to the structure, it also enhances privacy and blocks out unpleasant views. Although sheets of solid wooden boards installed above the posts achieve the desired purpose, consider using lattice sheets with square or diagonal patterns. Lattice sheets are available in 4-foot and 6-foot heights that measure 8 feet wide, so cut each sheet down to 2 feet and frame it before attaching it to a frame and nailing to the top of the fence.
Count the number of posts along the fence line and cut the same number of extension posts down to 2 feet in height using a saw.
Attach one end of a metal tie plate to an end of one 2-foot-tall extension post using four to six 1 1/4-inch screws. Also attach another plate to the other side of the same extension post, so both plates are parallel.
Stand an extension post over an existing corner post. Insert 6 screws through the holes along each metal tie plate that penetrate the existing post and join the two posts together. Repeat the process of joining the remaining 2-foot-tall extension posts to the remaining posts along the fence line.
Measure the space between adjacent posts along the fence line and cut a sheet of lattice to the same width. Also cut it down to 2 feet in height using a table saw.
Cut lengths of 2-inch-by-2-inch lumber to frame each lattice sheet. Use a miter saw to bevel-cut the edges of the wooden boards for frames at 45 degrees.
Position a router saw along a corner of a 2-inch-by-2-inch board and form a grove along its side into which an edge of the lattice panel will rest. Repeat the process of forming a groove along a side of each board.
Position an edge of the lattice sheet into a 2-inch-by-2-inch board and push so it fits snugly inside. Continue to frame each edge of the lattice panel, ensuring the beveled edges of sides rest against each other.
Drill three pilot holes through the end of each long framing board, and one through the corner of each short end. Insert a 2-inch screw into each hole to penetrate the wood and hold the structure together.
Enlist a helper to hold a framed lattice section directly above the existing frame between two adjacent post extensions. Use a carpenter's level to ensure it is level and plumb, or adjust its position if necessary. Join the frames at the sides of each lattice panel to the post using 3-inch screws.