Step 1: Cut and pry damaged board Use a saber saw to make a cut into the damaged board. Be careful to avoid nicking the adjoining planks. Use a pry bar to carefully lift the damaged board up off the joists. Remove the old fasteners as you go. A crowbar will give you better leverage in this process, so put a piece of wood down under the crowbar to protect the deck at the pivot point.
Step 2: Mark the joist locations on the removed board With the board lifted clear of the deck, locate the nearest joist. Use a square and a pencil to mark the center of joist on the board. Draw a line on the decking plank marking exactly halfway across the thickness of the supporting joist below. Repeat this step on the other end of the damaged plank, marking a line on the plank halfway across the thickness of the joist that supports that end of the plank.
Mark a line halfway across the thickness of the joist below.
Step 3: Cut the damaged board Lift each end of the damaged board up and support it with a piece of scrap wood. Using a circular saw, cut the decking plank along each marked line. Do this on both ends. Remove the damaged section of deck board.
Step 4: Measure and cut the replacement board Carefully measure the opening for the replacement board. Transfer the measurement to the replacement board, and lay down the cut lines with a square and pencil. Double check your measurements. Cut the new board.
Step 5: Install the replacement board Set the replacement board in place. Select a drill bit slightly smaller than the fasteners and drill two pilot holes on both ends of the new board. Using the same fasteners that were used on the rest of the deck, set the board in place by driving or screwing the fasteners into the pilot holes. Be sure that the fasteners are set below the surface of the wood.