Saber saw
Circular saw
Pencil
Posts (4x4s) cut to length
Chisel
Carriage bolts, or lag screws with washers
Spirit level
Drill and drill bits (and counterbore if you're countersinking the bolts)
Quality caulk (if you're countersinking the bolts)
Measuring tape
Railing construction methods vary, but most use the techniques below.
Typically, the railing posts are installed first, followed by the top and bottom rails, the top cap, and ending with the balusters. Alternatively, the rail sections can be built ladder-style and then installed between the posts.
1.
Mark Post Locations on the Fascia or Joists
On the fascia or joists, mark the position of all the posts, spacing them evenly wherever possible. Make square layout lines so that your posts will need little straightening later.
2.
Notch the Deck, If Needed
Use a saber saw to make any cutouts in the deck necessary to accommodate the posts. (Fig. 1)
3.
Cut and Notch the Posts
To determine the length of each railing post, start with the planned height of your railing (as measured from the deck surface). From this height, subtract the thickness of the top cap, and then add the thickness of the deck flooring plus the width of the joist.
For example, if you want a railing 40 inches high: subtract 1-1/2 inches for the thickness of the top cap, and then add 3/4-inch for the thickness of the deck flooring plus 8 inches for the width of the joist (if it's a 2x8); this will yield a post length of 47-1/4 inches. Cut all railing posts to the same length.
To notch each post to accommodate the deck, at one end of it mark a cutout 2 inches deep (half the width of your 4x4 post) and extend this cut up the post for a length equal to the width of your joist plus the thickness of the deck flooring. Cut the notch carefully with a circular saw--don't cut past the lines (Fig. 2). Use a chisel to finish the corners and clean up the cuts (Fig. 3).
The notch in a corner post will be cut differently to form a right angle; in this case, you're actually removing less wood (Fig. 4). Cut with your circular saw as far as you can without going past the lines. Chisel out the remainder with a sharp chisel.
4.
Drill Pilot or Screw Holes
Mark your posts for carriage bolts or lag screws. They should be within 1-1/2 inches of the top and the bottom of the joist and should not penetrate the deck flooring.
Have a helper hold each post in position, checking for plumb, while you drive the drill bit through the post and into the joist (Fig. 5).
If you have a long bit, just keep boring all the way through. If your bit is shorter than your screw or bolt, drill as far as you can, remove the post, and finish the hole.
If you're concerned about getting the posts plumb, first drill the top hole and temporarily insert the bolt or screw. Then hold the level to the post and drill the second hole.
5.
Attach the Posts
Secure the posts with carriage bolts or lag screws with washers (Fig. 6).
Some people prefer the look of countersunk bolts or screws. If you countersink them, fill the holes with a high-quality caulk to protect the open grain exposed by the counterbore.
