Keep both beauty and safety in mind when building railings.
You can construct your railings a number of ways, but the most common (and generally the easiest) is to attach the posts to the rim joists and headers and install railing sections between them. Most railing designs go up rails first, then balusters or infill, then the cap rail.
When installing the posts, overhanging decking can get in the way. You can either notch the post or notch the decking so the bottom of the post rests flat against the joist. Notched decking is the method illustrated on these pages -- it minimizes the possibility of weakening the posts.
Creating level lines is especially important in railing construction. That's because railing components are viewed against the background of the house. Exercise care when establishing level lines. For example, use a water level to mark the placement of the bottom of the posts. Using a line level or setting a carpenter's level on a long board will probably prove inaccurate over long spans. A 1/2-degree error at one end can mean a discrepancy of several inches at the other.
About 16 hours to cut and install railings for a 12x16-foot deck
Circular saw, miter saw, post level, 4-foot level, 2-foot level, cordless drill, spade bits, twist drill, socket wrench, spacing jig, hammer, square
Measuring, cutting, fastening, leveling
Lumber, fasteners, lag screws and washers
Calculate the post length: Start with its height above the deck and subtract the thickness of the cap rail. Add the height of the joist, less a 1-inch reveal. Cut all your posts to this length. Mark the reveal at one end of the joist and at the other end with a water level. Snap a line, and install the posts at the proper spacing.
Clamp a stop block to your miter saw table at the required baluster length and cut all the balusters. Bevel the bottoms and tops or make other decorative cuts. Calculate the necessary spacing between the balusters, then cut scrap wood to that width to use as a spacing jig. Set the jig in place, then a baluster, and fasten the baluster to the top and bottom rail. When you get within the last three or four balusters, check the remaining space and adjust the spacing slightly if necessary.
Miter the end of the cap rail (commonly a 2x6) and hold it in place to measure its length. The cap rail has to run to a corner, or, if jointed, the joint must be centered on a post. Mark the square end of the cap rail and cut it, making a scarf joint over a post. Always cut the miter first, then the end. Drive two fasteners on both sides of a joint and one every 12 inches between posts. Smooth the cap rail (both the top and the edges) with a pad sander.
Mitered cap rails dress up the appearance of your railing, but they are notorious for coming apart. First make sure that the edges fit together precisely. Recut them if they don't fit correctly. Apply a thin bead of construction adhesive to the faces of the miter and push them together, clamping them with a corner clamp if you have one. Drive finish nails into the top rail and posts and also into the corners.