Bracing a New Gate
Arrange the vertical boards for your gate in their final configurations on a level surface. Make sure all the boards are cut to the desired size, shaped if necessary and sanded. Place the boards face down, since you will attach the braces to the back of the gate.
Cut two lengths of wooden boards to the width of the gate to form horizontal braces. Trim excess wood on the braces so they are flush with the corner vertical posts.
Lay the two boards horizontally over the gate, several inches from the top and bottom of the structure. Predrill screw holes through the horizontal boards that penetrate the boards directly below, using a drill bit slightly smaller than the screw’s shank.
Insert galvanized builder’s screws through the holes to join the horizontal braces to the vertical boards, forming a rectangular gate.
Cut a wooden board to size so it stretches diagonally between the two horizontal cross braces. Lay it diagonally over the gate, with one corner above the latch and its other corner over the opposite end, forming a “Z.” Mark along the top and bottom corners of the board and trim excess length so it fits snugly between the horizontal braces.
Attach the diagonal board to the gate using galvanized screws. Your gate now has a Z bracing. Depending on personal preference, you can install the gate between the fence posts as it is or attach another wooden board diagonally over the structure, opposite to the first one, forming an “X.” You have to cut the second diagonal board into two pieces so it fits around the previous board. Install this diagonal board on the gate with screws.
Bracing a Sagging Gate
Push a tilted post to its original place to brace it and straighten the gate. Enlist a helper to hold the post straight while you pound 1-by-2-inch redwood boards 2 feet into the ground next to the post using a sledgehammer.
Examine the gate’s hinges if the post is straight but the gate still sags. Unscrew the hinges from rotting wood and reattach them to firm wood on the gate or replace with larger hinges. Remove the gate if the wood is completely rotted, and replace as necessary.
Reinforce the corners by screwing 3- to 4-inch exterior screws into each. Attach a corner bracket to the inner edge of each corner for added security.
Install a diagonal cross brace to make the gate more secure. Cut two lengths of lumber to fit between the corners of the gate, forming an "X." Screw one diagonal brace length to the gate using galvanized screws. Cut the second diagonal brace into two sections to go around the previous brace instead of overlapping it. Attach the two pieces to the gate to form the second diagonal brace, in the opposite direction to the first diagonal, thus forming an "X."