The first step in adding the railing to the deck is installing the post.
Assembling the parts
Draw your design and double-check the sizes and measurements. In this railing the post length equals the height of the railing above the deck plus the decking thickness, plus the joist width, minus the thickness of the cap rail. The baluster length equals the height of the railing above the deck minus the gap between the bottom of the railing and the deck (about 2 to 3 inches), minus the thickness of the cap rail.
Check codes for these requirements:
-- The minimum height of the railing.
-- Allowable baluster spacing.
-- How the posts attach to the framing.
-- The maximum space between the bottom of the balusters and the deck.
You may be able to buy precut balusters and posts that fit your design requirements.
Posts are as long as the height of the railing, plus the width of the joist and the thickness of the decking, minus the thickness of the rail cap. Set up a jig that allows you to cut all the posts to the correct length. A 22-1/2-degree angle cut on the bottom adds a decorative touch.
Mark for two holes in the posts that are each 1 inch from opposite sides of the post and 1-1/2 inches from the top or bottom of the joist. Drill holes the same diameter as the carriage bolts you will use (Step 4). Staggering the holes avoids splitting the post along the grain lines.
For each post cut a notch in the decking so the post can fit tightly against the joist. Use a professional-quality jigsaw for this -- it's difficult to cut straight with a cheap model. Cut the notches with 1/8 inch of play to allow for expansion and so you won't have to force the post in.
Notched posts take time and experience to cut, but make a pleasing finishing touch for a deck railing. They draw the baluster up closer to the deck edge and make a slightly firmer joint than surface-mounted posts.
Mark the posts for a notch that is 1-1/2 inches deep and as long as the depth of the joist -- about 7-1/2 inches for a 2x8 joist, about 9-1/2 inches for a 2x10. (Use a joist scrap to be exact.) Add the thickness of the decking and mark for the crosscut.
Cut the notch
Make a crosscut where the notch ends. With the saw set to maximum depth, cut the long lines on each side without cutting beyond the crosscut. (For a corner post, set the blade to a depth of 1-1/2 inches and make two long cuts.)
Chisel away the excess
Use a hammer and chisel to crack out the waste -- it will neatly pop out as one piece. Then chisel away the remnant where the saw blade could not reach.
Complete the corner post
Make the long cuts and a shallow crosscut. Chisel toward the crosscut and split out the waste. Chisel down along the crosscut and along the long cuts to remove the remnant of wood remaining.