How to Build a Stair Rail for the Outside

Choose decay-resistant wood for your stair rail project. Railings can be your preferred thickness, but should be at least 1 1/16 inches thick for best stability and strength.

Secure the two four-by-four posts at the top and bottom of your stairs' stringer, which is the part of the stairs creating the rise and holding the wooden steps (or treads) in place. Attach the posts using the hex bolts and a level to make sure they are straight. Leave the posts extending 36 inches above the stairs' treads.

Measure from the bottom of the posts to 34 inches and mark the wood at this spot. Measure from that mark down 6 inches where the railing will be, and make marks on the posts.

Trim the posts to 34 inches at the marks you made so the tops create a 45-degree angle or the same angle as your stairs.

Cut two lengths of railing the same size to form the top railing. Nail one piece on the outer side of the posts with one edge of the railing flush with the tops of the posts. Nail the other piece in place as the railing cap (or top) so its shorter edge is flush with the side of the railing you just attached.

Saw the second railing to the same length as the span of the entire railing. Secure by nailing to the outer edge of the posts at the 6-inch marks you made on the posts.

Trim the second railing, using a measuring tape and bar level to achieve a straight cut perpendicular to the ground.

Sand the edges of your railings until smooth and paint if desired.