How to Install Deck Railing Posts

A railing is one of the most visible parts of a deck and a critical safety feature. Keeping both factors in mind when planning how to install railing posts is essential. Choose lumber, for example, that's free of cracks and splinters. After the railing is installed, sand all the corners smoothly.

Before you begin, draw your design and double-check the sizes and measurements. In our 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.

Also make sure to check local codes and include any requirements in your plan. Some common considerations include:

• 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.

What You Need

• Deck posts
• Circular saw
• Pencil
• Measuring tape
• Drill
• Jigsaw
• Post level
• Hammer
• Carriage bolts
• Washers
• Nuts
• 5-inch lag screws
• 2x4

Step 1: Cut Posts

Posts are as long as the railing's height, plus the joist's width and the decking's thickness, minus the rail cap's thickness. 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.

Step 2: Mark and Drill Holes

Mark for two holes in the posts, 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. Staggering the holes avoids splitting the post along the grain lines.

Step 3: Cut Notches

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, so you won't have to force the post in.

Step 4: Clamp the Post

Clamp the post so it's plumb in both directions. Drill into the existing holes and through the joist. Tap carriage bolts all the way through. Under the deck, slip on a washer and tighten a nut for each bolt.

Step 5: Fasten a 2x4

Where the railing meets the house, use 5-inch lag screws and washers to firmly fasten a 2x4. This is stronger than a 4x4 post attached to the deck.

How to Make Notched Posts

Notched posts take time and experience to cut but make a pleasing finishing touch for a deck railing. They draw the baluster closer to the deck edge and make a slightly firmer joint than surface-mounted posts.

Mark the posts for a notch 1-1/2 inches deep and the joist's depth— 7-1/2 inches for a 2x8 joist, 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 the long cuts to remove the remaining remnant of wood.