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How To Install Outdoor Stair Railing

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outdoor wood stair railing

An outdoor stair railing is required when you’re deck or patio is over 30 inches high. Sometimes you might still want to build a stair railing even if your patio isn’t 30 inches high.

As you get older, a stair railing is very helpful to climb stairs, even if it is one or two steps. Having something to hold on to helps your stability when you’re going up or down your stairs.

A friend just bought a house that had a remodeled pool patio. Their insurance inspector told her she needed to build a railing for her stairs or they would cancel her insurance.

So we built an outdoor wood stair railing this past weekend. Her perimeter fence near the pool is horizontal slats so we stayed with that theme for her railing.

In all it took about 4 hours to complete this project not counting going and getting the materials from the local box store.

Materials Needed

  • (4) 4x4x8 pressure treated posts
  • (8) 1x6x8 pressure treated wood for rails
  • (2) 5/4x6x8 pressure treated decking for top hand rail
  • (4) 50 lb bags of fast concrete
  • (1) 50 lb bag of gravel
  • (1) box of 2.5 inch long deck screws

Tools Needed

  • post hole digger
  • empty gallon jug
  • drill
  • speed square
  • circular saw
  • reciprocating saw
  • sander
  • clamps
  • level
  • 2×4 for tamping ground

Installing Outdoor Stair Railing Posts

This stair railing needed 4 post holes for the stair railing. We decided to install a buried posts next to the concrete patio rather than install the post on top of the patio.

Since there was no railing required for the rest of the patio, it was easier to bury the post than attach it to the top of the patio pavers into the concrete below.

We mark out post locations and start to dig everything out with the post hole diggers. We dig to 30 inches for each hole. After tamping the bottom of the hole, we put in 5-6 inches of gravel at the bottom of the hole. This key for drainage so water doesn’t sit at the bottom of the post and it rots faster.

We insert the post in the hole and tamp the gravel with the bottom of the post. We put a level on the post and have a second person hold the post steady as we pour in the concrete.

Using Fast Setting Concrete

The fast setting concrete is great for setting posts fast. The concrete sets in 30 minutes allowing you to finish your project faster. It also is great for not having to mix the concrete before it goes into the hole.

I used to be a skeptic of fast setting concrete until I saw this video showcasing how the water seeps down into the entire bag of concrete in a see through bucket.

Simply pour your bag of concrete into your hole, being careful not to inhale the concrete dust that blows back up in your face. Pour your gallon of water on top of the concrete and wait until it’s all drained away.

DO NOT put any dirt back into the hole until the concrete is set. If you shovel dirt in the hole while the water is still there, the water will soak into the dirt, not the concrete mix.

We wait for about an hour to make sure everything is set before we cut the top of the posts.

How to Cut 4×4 Post After Installation

To cut down the posts, we measure where our top horizontal rail will be located. Clamping the 1x6x8 on the side of each post, we determine the correct height at each post so the railing is 35 inches high going down each stair.

clamped rail onto 4x4 post

The hand rail is 1 inch thick will make the total rail height 36 inches. Always measure the front of each step to get the correct measurement for the rail.

We marked the rail location on all sides of the post with a speed square. Keeping the rail as a guide, we used the reciprocating saw to cut the post down to the final height.

speed square next to post and rail

Keeping the saw blade straight through the back side of the post is key to getting a good straight angled cut. As you can see on the pictures, we had an initial measurement that wasn’t correct and had to measure again. Always measure several times before you make your final cut!

top of post cut to size

Installing The Outdoor Stair Rails

If you’re installing horizontal railing, you need to make sure the height is the same from the top of each post to the bottom of the stairs. This will help keep the spacing between the rails even down to the bottom of the stairs.

We will be running the rails long past each post and cutting them down after installation. Another way is to mark the backside of the clamped rail and then cut along the marked line with a miter saw or circular saw.

We attached the top rail with (4) screws in each post. You can attach in a square or parallelogram pattern to follow the angle of the rail.

We then clamped the bottom of rail and measured the distance between the top and bottom rail. We had 21 inches from the bottom of the top rail to the top of the bottom rail.

Knowing that we need to keep less than a 4 inch gap between boards, we could calculate how many boards we needed and the gap between each rail.

21 inches divided by 11 (two 5.5 inch wide rails in between the top and bottom rail) gave us 10. There is 3 gaps between 4 rails. 10 divided by 3, gave us 3.33 or 3 5/16 of an inch gap between rails.

Now we can simply measure down 3 5/16 from top rail to install the 2nd rail and then repeat with the 3rd rail.

Now that we have one side of the railing finished, rather than doing a lot more math for the second railing, we will use a level to mark everything to be cut.

We marked the posts first to cut them off and followed with the top rail on down to the bottom rail. By keeping everything level between the two railings we saved a ton of time rather than going through the process of calculating all the heights again for everything.

wood stair rails

Installing the Top Hand Rail

Before we install the top hand rail, we’ll cut the rail excess away with a reciprocating saw and sand any excess with a belt sander. If you’re unsure if you can cut a straight line with a reciprocating saw, you should simply mark the board and cut before installation.

With everything cut down, we can now start marking where to cut our hand rail. We went with 8 inches hanging over each post. We installed the top rail to each post using (4) screws in a square pattern.

Once the top rail is installed, we marked the cutoff line and used our circular saw to cut the rail. Since the rail is at an angle, we adjusted our circular saw plate so that the cut was perpendicular to the ground.

We then used a speed square as a guide for the circular saw to keep everything straight. Always use your speed square guide on the good side of the board and not the cut off side.

Now you’re ready to use your sander to round off any cut edges from the top rail. Using the decking as a top hand rail saves time as the board’s edges are already rounded off.

sanding the top hand rail


With everything installed and sanded down, you can now admire your new outdoor stair rail. This rail will last a long time and help you up and down the stairs for many years to come. If you’re not a fan of the pressure treated wood color, you can always stain the rail after the wood is dry.

If you’re wondering which is better, paint of stain for pressure treated wood we have more details in a different article and if you need more deck railing ideas we have that covered as well.

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Jena Slocum Co-Founder

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