If your home's stair stringer has seen better days you need to replace it. Stair stringers are the angled pieces of wood that the steps rest on and maintain their stability and height. Over a long period of time, wood will begin to deteriorate naturally due to moisture trapped inside of finished wood. When this occurs you should replace the stringer before it becomes a hazard to you, your family and your guests.
Step 1 - Prepare the Area
Use the pry bar to remove the stairs and the stringers to be replaced. Pull out any exposed nails left in the stringers to keep them from causing anyone harm. Under the deck joist, attach measured and cut 2x6 boards for the stair stringers to be attached to. This will ensure a reliable surface for your stringers to hold on to. At the base of the 2x6, measure up 7 1/4 inches, and mark the place for attaching the stringer. This measurement is the size of each "step" on the stringer. Directly beside the marks, you made on the 2x6, clamp and then screw a block of 2x4. The purpose of the block is to provide extra support and surface to attach the stringer securely to the deck. Dig a hole and put a concrete paver in it, make sure it is level. This will be where the base of the stringer sits, keeping it drier and less likely to deteriorate in the future.
Step 2 - Prepare the Stringer
Depending on the height of your deck, you may need to cut off part of the stringer to accommodate the height. Saw off excess length in the stringer. Drill guide holes in the stringer and deck. Make sure the guide holes are smaller than the nail or screw or they will not hold properly and the stairs will begin to creak. This will help to eliminate cracking or splitting of the wood, which can easily happen when nailing or drilling so close to the edge of the wood. Install the stringer to the deck using three-inch nails or screws attached at an angle from the stringer into the deck, and others straight through the stringer into the cleat (block of wood).
Step 3 - Attaching Additional Stringers
If you need to replace more than one stringer you should know how many you will need. They should be spaced about 30 to 32 inches apart to maintain strength in the step assembly. Each should have the same height and should be level to the ones to each side of it. Concrete paver blocks should be placed in the ground at the same height for each stringer.
Step 4 - Attaching Stairs to Stringers
Attach each stair slat to the stringers. Use a single nail or screw in each slat until you are sure that your stairs are level. Once you're confident that the stairs and the stringers will maintain their consistency and keep level then attach two more screws at each stringer to keep the stairs secure to the stringers.