How to Install Deck Railing Posts
A railing is one of the most visible parts of a deck, but it's also a key safety feature. When planning out railing posts, it's important to keep both factors in mind. Choose lumber, for example, that is free of cracks and splinters. After the railing is installed, sand all the corners smooth.
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:
What You Need
- Deck posts
- Circular saw
- Measuring tape
- Post level
- Carriage bolts
- 5-inch lag screws
Step 1: Cut Posts
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.
Step 2: Mark and Drill Holes
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. 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 and so you won't have to force the post in.
Step 4: Clamp the Post
Clamp the post so it is 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 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.