Step-by-Step Log Railing Installation Guide

Installing a round log railing is a test of patience, precise measuring, and specialized joinery. Unlike working with dimensional lumber where every piece is perfectly square, every single log in a rustic railing is unique. It tapers, it bows, and it features irregular knots.

To build a structurally sound and visually stunning log railing - specifically a classic peeled log system utilizing traditional mortise and tenon joinery - you must abandon the tape measure as your only source of truth and embrace scribing, leveling, and custom-fitting every joint.

This guide provides a comprehensive, sequential workflow for installing a standard log railing section (posts, top/bottom rails, and vertical balusters).

Note: If you are building an exterior railing on an elevated deck, please consult our specific Deck Installation Guide for critical information regarding structural attachment to the deck framing and weatherproofing.

Phase 1: Planning and Post Layout

The foundation of any strong railing is the posts. Everything else is simply fitted between them.

1. Determine Post Locations and Spacing

• The Code: Most building codes (IRC) require posts to be spaced no further than 6 to 8 feet apart to ensure the top rail can withstand a 200-pound concentrated load without catastrophic deflection.
• The Aesthetics: Visually, shorter spans (5 to 6 feet) often look better with thicker logs, preventing the railing from looking “spindly” or stretched.
• The Mark: Snap a chalk line indicating the center-line of your railing. Mark the exact center point for every post along this line.

2. Plumb and Secure the Posts This is the most critical structural step. A wobbly post guarantees a failing railing.

• Interior Subfloors: If building indoors on a plywood subfloor or stair stringer, you cannot simply toe-nail a massive log. You must use heavy-duty structural screws driven up through the subfloor into the bottom of the post, or utilize hidden internal steel brackets (like a knife plate or heavy steel pin system) that drop the massive log post down onto a rigid steel anchor bolted to the floor joists.
• Plumb, Not Level: Round logs are never “level” on their faces. You must use a long level on multiple sides of the post, finding the general center-line, to ensure the post is standing vertically plumb. Temporarily brace the post with scrap lumber once plumb.

Phase 2: Preparing the Horizontal Rails

With the posts rigidly secured, you must size and fit the top and bottom rails.

3. Measure and Cut the Rails to Length

• The Challenge: You cannot simply measure the distance between the two posts with a tape measure because the posts are round; the distance between them changes depending on where exactly on the curve you measure.
• The Solution (Scribing): Hold the oversized bottom rail horizontally between the two posts at the desired height. Ensure the rail is perfectly level. Using a compass or a set of scribes, trace the exact curvature of the vertical post onto the end of horizontal rail.
• The Cut: Carefully cut along this scribed line (usually with a sharp chainsaw, reciprocating saw, or large band saw). The shaped end of the rail should now fit perfectly against the curved face of the vertical post. Repeat for the other end, and then for the top rail.

4. Mark the Baluster Spacing (Layout) Before assembling the rails to the posts, you must lay out where the vertical balusters will go. You do this with both rails laying side-by-side on the floor.

• The 4-Inch Rule: Building codes dictate that a 4-inch sphere cannot pass between balusters. Because logs are irregular, you should aim for a center-to-center spacing that leaves no more than 3.5 inches of gap between the narrowest points of the balusters.
• The Match: Lay the top and bottom rails parallel to each other on the floor. Find the exact center-line of both logs. Mark your baluster spacing precisely along these center-lines. Crucially, ensure the marks on the top rail perfectly mirror the marks on the bottom rail.

5. Drill the Mortise Holes Using a massive, heavy-duty low-RPM drill equipped with a Forstner bit, hole saw, or specialized mortising bit, drill the holes into the rails at every mark you just made.

• Depth: The mortise holes typically need to be 1.5 to 2 inches deep.
• Angle: The holes must be drilled perfectly perpendicular to the center-line of the log. If you drill at a slight angle, the baluster will sit crooked. Consider building a simple wooden jig to keep your drill perfectly upright on the curved log surface.

Phase 3: Preparing the Balusters

Now you must create the pegs (tenons) that will fit into those holes.

6. Cut Balusters to the Correct Length Determine your final desired top rail height (usually 36" or 42"). Subtract the thickness of the top rail and the height of the bottom rail off the floor. This gives you the visible length of the baluster. Now, add the depth of the two mortise holes (e.g., add 3 inches total if drilling 1.5-inch deep holes). This is your final cut length.

7. Cut the Tenons This requires a specialized tool called a tenon cutter. It resembles a massive, heavy-duty pencil sharpener that chucks into a powerful drill (often a 1/2-inch drill).

• The Process: Clamp the baluster securely in a heavy vise. Drive the spinning tenon cutter straight down onto the end of the log. It peels away the outer wood, leaving a perfect, smooth cylinder (the tenon) in the center.
• The Fit: The tenon diameter must exactly match the mortise holes drilled in the rails. Common sizes are 1.5-inch or 2-inch tenons. Cut tenons on both ends of every baluster.

Phase 4: Assembly (Putting the Puzzle Together)

This is the hardest physical phase. It often requires two people.

8. Dry Fit the Panel Lay the bottom rail on the ground. Insert every single baluster tenon into its corresponding mortise hole. It should be a tight, squeaky fit (use a heavy rubber mallet to tap them home). Once all balusters are standing up, carefully lower the top rail onto the balusters, guiding each tenon into its upper mortise.

• Tip: Lightly beveling the edges of the tenons with sandpaper makes them guide into the holes much easier.

9. Secure the Joints (Optional but Recommended) While a tight mortise and tenon joint is strong, logs shrink as they dry in a house. To prevent the balusters from spinning or eventually dropping out, you can secure each joint.

• Pinning: Drill a small hole through the side of the rail, passing directly through the hidden tenon inside, and pound a wooden dowel (or structural screw) into the hole.

10. Install the Fully Assembled Panel With the help of a partner, lift the entire massive, assembled railing section (bottom rail, balusters, and top rail) into place between the two plumbed posts.

• The Connection: You must now secure the heavy scribed ends of the horizontal rails to the vertical posts.
• The Fasteners: Do not use drywall screws or small trim nails. You must use massive structural timber screws (like GRK or TimberLOK fasteners) or heavy lag bolts. Counter-sink these massive screws deeply into the side of the rail, driving them deeply into the meat of the vertical post. You can then plug the counter-sink holes with matching wooden plugs for a seamless, rustic look.

Phase 5: Final Finishing

11. Sanding and Cleanup Once structurally secure, walk the railing with an orbital sander or sanding sponges to knock down any harsh splinters, smooth out the wood plugs over your fasteners, and clean up any pencil marks or chalk lines.

12. Apply the Finish Apply your chosen protective finish. If the railing is indoors, a high-quality penetrating oil or clear polyurethane will bring out the rich colors of the wood. Never skip finishing. The finish protects the wood from hand oils and prevents the bark edge from drying out and separating from the log.

Installing a log railing is slow, methodical work. It forces a builder to slow down, read the wood, and appreciate the craft of traditional joinery. The breathtaking result, however, is a structural element of undeniable character that will outlast the occupants of the home.