Just as a decorative wood railing serves the purpose of preventing falls from a deck or outdoor landing, its counterpart, an exterior stair railing, makes access to the deck or landing safer. The wooden handrail can be a simple extension of the wood railing on the deck, or it can be an elaborate creation with balusters on the rail posts and other decorative trim. The main purpose is to provide a sturdy wooden handrail. If you have carpentry skills, you can add a wooden handrail to an outdoor wood stair.
Pull off the tread to the bottom step. Use a screwdriver to remove the screws. Pry the wood up with a pry bar.
Install the bottom handrail post inside the tread frame. Make sure it aligns with the post at the top of the stairs. Use a level to make sure the post is plumb and square with the stair treads. Secure it to the inside of the stringers, or stair treads, with angle braces and screws. If it's a long run of stairs, you may need to add one or more intermediate posts to the inside of those stair treads as well. Not only does this give additional support, but it also should mirror the design and frequency of posts that surround the deck or landing area. To add the posts, repeat the process for the bottom step.
Hold the top rail for the wooden steps at the angle that parallels the down slope of the steps. It helps if you have someone to help you hold the wood while you measure. Use a pencil to mark where you need to cut the wood on both ends. The top of the wood rail needs to be flush with the top of the rails surrounding the landing or deck minus the width of the top rail board you plan to use. The bottom mark needs to be even with the bottom edge of the bottom post. Repeat these measurements for the bottom rail.
Cut the top and bottom rails with a circular saw. Screw them to the sides of their respective posts. Make sure the top and bottom rails parallel each other.
Measure the new length of the old stair tread with a tape measure. Cut it to fit and reattach it with screws so you can once again easily use the stairs.
Cut the angles on each end of a spindle to fit to the top and bottom rails. Once you get the first spindle's angles correct, use it as a template to cut the rest of the spindles you need to install on the handrail.
Pre-drill the holes for the spindles using a drill. Screw them into position, making sure you space them to match the rest of the deck or landing.
Measure and cut a cap rail for the project. Attach it to the top rail with screws. If you want the top of the bottom post to have a matching angle, cut the top off before you attach the cap rail. Use a sander to smooth any rough edges. If you wish, you can bevel the edges to make the cap rail easier to grip.
Check with your local building code office before starting this project. Some municipalities require that handrails be narrow enough to grasp. If that's the case in your town, adjust the width of the cap rail accordingly.
Wear protective equipment, such as goggles, when using power tools.