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How to Build a 2×4 Deck Rail on a Concrete Patio

Bob Jackson
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by Bob Jackson

This project explains how to build a deck rail from scratch using pressure treated lumber and mount the rail on a concrete patio using concrete wedge anchors.

Deck Rail Installation Overview

The house sits on a hillside and the basement level concrete patio lacked a deck rail, giving the house an unfinished look. I built a 25 inch high deck rail from scratch using pressure treated lumber and corrosion resistant wood screws. At 25 inches high the deck rail is low enough such as not to block the view, just right for sitting on and high enough to keep my dogs taking shortcuts through landscaping. The 4×4 end posts are mounted on 1/2 inch threaded concrete anchors and tied into the main 8×8 deck supports as shown here. The deck rail was painted with a redwood stain:

Deck Rail on a Concrete Patio
Deck Rail on a Concrete Patio

The end view of the deck rail illustrates the 4×4 end post, 2×4 cap and face board construction technique. Note the Simpson Strong-Tie CPS4 black plastic post standoff at the bottom of the 4×4.

Deck Rail Construction - End View
Deck Rail Construction – End View

Building Code Compliance

A deck rail is required is required when the deck (or concrete slab in this case) is 30 inches or more above grade (ground level). My basement slab varies from even with the ground to a foot or two above grade so a guardrail isn’t required by code. See How to Build a 2×6 Porch Rail and How to Build Code Compliant Deck Railing if you need a full height compliant guardrail.

How to Build a 2×4 Deck Rail on a Concrete Patio

The deck rail enclosed most of the concrete patio, except for a ~4 foot gap between the house and the deck stairs as shown below. My dogs would run through here and mess up the pine straw. Here’s how I built a deck rail section to close the gap.

Deck Rail Gap between House and Deck Stairs
Deck Rail Gap between House and Deck Stairs

Jumping ahead – here’s the finished deck rail, ready to be stained when the weather warms up. Not the gap between the house wall and the deck rail so there’s space to paint the wall but not so narrow as to catch leaves. A ~2 inch gap between the bottom rail and concrete patio provides room for leaves to pass under when using the leaf blower.

Build a Deck Rail on a Concrete Patio
Build a Deck Rail on a Concrete Patio

Deck Rail Building Materials

The materials for this project are:

  1. Pressure treated 4″x4″x8′ posts
  2. Pressure treated 2″x4″x8′ boards
  3. Pressure treated 2″x2″x8′ boards for balusters – I space my baluster 3-1/2 inches apart
  4. Concrete wedge anchors – 1/2 inch diameter by 5-1/2 or 6 inches long
  5. Simpson Strong-Tie CPS 4×4 plastic post standoffs
  6. 3-1/2 inch and 2-1/2 inch corrosion resistant deck screws

You’ll need to measure and figure up the quantity of lumber and supplies necessary for your particular project. I begin by making a free hand drawing of the layout and measurements. Next I total up the materials to prepare a shopping list. Keep in mind how the lumber will be cut to minimize waste. It may be better to use 10- or 12 foot lengths of lumber for less waste and/or fewer joints.

The materials for this small project are laid out below after measuring and cutting the lumber:

Build a Deck Rail: Materials Ready for Assembly
Build a Deck Rail: Materials Ready for Assembly

Build the Deck Rail

I started by cutting the 4×4 end posts to 21 inches in length using a Dewalt Miter Saw. I can’t say enough about how useful a power Miter Saw is for making quick precise cuts at different angles. The usual statements apply when working with a power saw – be careful our you’ll loose a finger! – and wear safety glasses. I always do. Honest.

Build a Deck Rail: Saw the 4x4 Posts with a Miter Saw
Build a Deck Rail: Saw the 4×4 Posts with a Miter Saw

The balusters are marked off at 19 inches in length on a 2x2x8 square post. At 19 inches long, I can get five (5) complete balusters from an 8 foot (= 96 inches) post with only 1 inch of waste: 19 * 5 = 95 inches.

Build a Deck Rail: Measure Balusters on a 2x2x8 Square Post
Build a Deck Rail: Measure Balusters on a 2x2x8 Square Post

The seven (7) balusters I needed are cut to 19 inches long:

Build a Deck Rail: Balusters Cut to 19 inch Length
Build a Deck Rail: Balusters Cut to 19 inch Length

The balusters start out with square flat ends. The miter saw is set to 35 degrees as shown below. The bottom end of the baluster will be cut at a 35 degree angle to form a drip edge to encourage water runoff. If the bottom end were left flat, water would tend to pool and encourage rot.

Build a Deck Rail: Baluster Drip Edge to be Cut at 35 degrees
Build a Deck Rail: Baluster Drip Edge to be Cut at 35 degrees

The miter saw blade is lowered with the motor off to position the blade before making the cut. I like to leave a 1/4 wide lip so as not to weaken it with sharp point. The baluster end profile will be a “blunted cheese wedge”.

Saw Deck Rail Baluster Drip Edge: Align the Blade
Saw Deck Rail Baluster Drip Edge: Align the Blade

Profile view of the baluster drip edge. Click on the image for a full size image.

Build a Deck Rail: Baluster Drip Edge Saw at 35 Degrees
Build a Deck Rail: Baluster Drip Edge Saw at 35 Degrees

The finished stack of balusters showing the bottom angle and drip edge.

Build a Deck Rail: Balusters Sawn with Drip Edge
Build a Deck Rail: Balusters Sawn with Drip Edge

Install Concrete Anchors for the 4×4 Posts

The centers of the posts are marked with a + on the concrete as shown near the drill bit. In my case the deck rail is 43″ long. A 4×4 post is actually 3.5 inches x 3.5 inches. To find the distance between the post centers I subtract 1/2 width of each post, or 1-3/4 inches:

43 inches total width minus 1-3/4 inches (left post) minus 1-3/4 inches (right post) = 39-1/2 inches distance between the post centers.

To mark the post centers:

  1. Locate the right post and mark the center as shown below.
  2. Measure 39-1/2 inches to the left and mark the center of the other post.
  3. Drill 1/2 inch holes with a hammer drill for the concrete wedge anchors.
Build a Deck Rail: Drill the Hole for the Concrete Anchor
Build a Deck Rail: Drill the Hole for the Concrete Anchor

I used 1/2 inch x 5-1/2 inch threaded concrete anchors as shown.

Red Head - Trubolt Concrete Wedge Anchor 1/2
Red Head – Trubolt Concrete Wedge Anchor 1/2″ x 5-1/2″

Concrete wedge anchors have a metal sleeve on the tapered bottom end that grabs tight when the anchor is pulled against the hole by the threaded nut. These anchors work extremely well.

Red Head - Trubolt Concrete Wedge Anchor
Red Head – Trubolt Concrete Wedge Anchor

The concrete anchors must be set at least 2-1/4 inches deep. Drill the hole about 1 inch deeper (or 3-1/4 inches total) to allow for dust accumulation at the bottom of the hole.

Build a Deck Rail on a Concrete Patio: Check Hole Depth for Concrete Anchor
Build a Deck Rail on a Concrete Patio: Check Hole Depth for Concrete Anchor

Mark the minimum depth line on the anchor (blue line) and tap the anchor into the hole. The 3-1/2 lb sledge hammer as shown here is more than enough for the job.

Build a Deck Rail on a Concrete Patio: Install the Concrete Anchor
Build a Deck Rail on a Concrete Patio: Install the Concrete Anchor

Place the washer and nut on the anchor and tighten. The anchor should grab fast with almost no slippage.

Build a Deck Rail: Concrete Anchor Bolt for the 4x4 Post
Build a Deck Rail: Concrete Anchor Bolt for the 4×4 Post

The concrete wedge anchor is set fast and tight:

Build a Deck Rail: Concrete Wedge Anchor
Build a Deck Rail: Concrete Wedge Anchor

Install the 4×4 Deck Rail Posts

Drill a 1/2 inch hole in the bottom of the 4×4 posts to slide the post over the anchor pin.

Locate the center of the post by measuring and marking 1-3/4 inches on each side as shown by the black tick marks:

Build a Deck Rail: Measure 1-3/4 Inches to Locate the 4x4 Post Center
Build a Deck Rail: Measure 1-3/4 Inches to Locate the 4×4 Post Center

Use a square to mark a straight line across the tick marks on each side to locate the center of the 4×4 post.

Build a Deck Rail: Mark a Line at 1-3/4 Inches per Side of 4x4 Post
Build a Deck Rail: Mark a Line at 1-3/4 Inches per Side of 4×4 Post

The center of the 4×4 post is now located at the cross hair to drill the 1/2 inch hole to receive the pin of the concrete anchor wedge.

Build a Deck Rail on a Concrete Patio: Center of 4x4 Post Marked
Build a Deck Rail on a Concrete Patio: Center of 4×4 Post Marked

Drill a 1/2 inch diameter hole in the center of the post to receive the pin of the concrete anchor. I use DeWALT “pilot” type drill bits that prevents the large drill bit from “walking” when starting the hole. Drill the hole about 4-1/2 inches deep.

Take care to drill the hole vertical (i.e. not canted to the side). I use the carpenters square to periodically check my drill alignment with the post.

Build a Deck Rail: Drill a 1/2 Inch Hole for the Concrete Anchor
Build a Deck Rail: Drill a 1/2 Inch Hole for the Concrete Anchor

Test fit the anchor wedge to verify the hole is deep enough and the hole is vertical with the post.

Build a Deck Rail: Trial Fit the Concrete Anchor
Build a Deck Rail: Trial Fit the Concrete Anchor

Place the post standoff over the pin to check the overall fit and assembly:

Build a Deck Rail on a Concrete Patio: Post Standoff and Concrete Wedge Anchor
Build a Deck Rail on a Concrete Patio: Post Standoff and Concrete Wedge Anchor

The post standoffs are attached with four 2-1/2 inch corrosion resistant deck screws as shown.

Fasten the 4x4 Deck Post Standoff with Screws
Fasten the 4×4 Deck Post Standoff with Screws

Set the 4×4 post on the concrete anchor pin to check the overall fit. Repeat for the above procedure for the other post.

Build a Deck Rail on a Concrete Patio: Set the Post on the Anchor Pin
Build a Deck Rail on a Concrete Patio: Set the Post on the Anchor Pin

Attach the 2×4 Rails to the 4×4 Deck Posts

I pre-drilled the screw holes with a slightly smaller diameter bit than the screw to prevent the deck rail wood from splitting.

How to Build a Deck Rail: Drill Pilot Holes for the Wood Screws
How to Build a Deck Rail: Drill Pilot Holes for the Wood Screws

Next, fasten the 2×4 top deck rail to the 4×4 posts and verify the top rail is level.

How to Build a Deck Rail: Fasten the 2x4 Top Rail to the 4x4 Deck Posts
How to Build a Deck Rail: Fasten the 2×4 Top Rail to the 4×4 Deck Posts

It turns out the concrete deck is sloped away from the house (this is normal for rainwater runoff) and the left post is about 1/2 inch too high. I used the carpenters level to mark the proper height and angle as shown and cut the post to the correct length on the Mitre Saw. This is an instance where using wood screws makes disassembly and corrections easy compared to nails!

Trim the Left 4x4 Post to Level the Deck Rail
Trim the Left 4×4 Post to Level the Deck Rail

Locate the bottom rail at least 2 inches high (to avoid catching leaves) and set a single wood screw only on the left end – this allows opposite end to rotate for leveling. Level the right end as shown and fasten the two screws. Then fasten the remaining screw in the left end.

Build a Deck Rail on a Concrete Patio: Install the Bottom Rail
Build a Deck Rail on a Concrete Patio: Install the Bottom Rail

The 2×4 face rail is attached with 3-1/2 inch screws evenly with top rail as shown. The balusters are laid out to show the overall progress.

Build a Deck Rail on a Concrete Patio: Balusters and Deck Rail Frame
Build a Deck Rail on a Concrete Patio: Balusters and Deck Rail Frame

Attach the Balusters to the Deck Rail Frame

So far, the deck rail frame is just sitting on the concrete anchor pins. It’s a snug fit, but the frame can be removed by lifting straight up such as not to bind sideways on the pins. Since frame is small, I lifted it off the anchor pins and laid it face down on the patio for easy access.

To attach the balusters to the frame:

  1. Pre-drill the screw holes in the balusters, otherwise the 2×2 post will split.
  2. Screw the 1st baluster to the frame with 2-1/2 inch corrosion resistant deck screws.
  3. Use a 2×4 block to set the gap to the next baluster and fasten it with screws.
  4. Move the 2×4 block to the next position, fasten the next baluster, repeat.
Build a Deck Rail on a Concrete Patio: Install the Balusters
Build a Deck Rail on a Concrete Patio: Install the Balusters

Move the 2×4 spacer block over and attach the next baluster. Repeat for the remaining balusters. Note the baluster drip edge is facing the bottom 2×4 rail for a pleasing look.

Build a Deck Rail: 2x4 Spacer Block to Set the Balusters
Build a Deck Rail: 2×4 Spacer Block to Set the Balusters

The newly assembled deck rail section is shown with the main deck rail (red) for comparison:

Build a Concrete Patio Deck Rail: Assembled Deck Rail
Build a Concrete Patio Deck Rail: Assembled Deck Rail

Deck Rail Final Assembly

The deck rail section is set on the concrete anchor pins. At this point, the deck rail is very rigid and fits snugly on the pins; any attempt at sideways movement will cause the 4×4 end posts to catch and bind on the 1/2 inch steel anchor pins.

Concrete Patio Deck Rail Mounted on the Anchor Pins
Concrete Patio Deck Rail Mounted on the Anchor Pins

Side view of the deck rail:

Concrete Patio Deck Rail - Side View
Concrete Patio Deck Rail – Side View

To plumb and deck rail and ensure there will be no movement, I used Simpson Strong-Tie angle connectors and screws to attach it to the 4×4 deck rail post to the 4×4 stairwell post.

Simpson Strong-Tie Screws and Metal Angles
Simpson Strong-Tie Screws and Metal Angles

I plumbed the deck rail using a level – it needed to lean forward about 1/2 inch to be vertical.

Build a Deck Rail: Plumb the Deck Rail Front-to-Back
Build a Deck Rail: Plumb the Deck Rail Front-to-Back

Then fastened the metal angle plate as shown in the next photo. Doing so fixed the deck rail in place very securely – almost no wiggle in any direction with heavy force.

Concrete Patio Deck Rail: Simpson Strong-Tie Connector Plate
Concrete Patio Deck Rail: Simpson Strong-Tie Connector Plate

Here’s how the completed deck rail looks. Note the short 2×2 section on the lower right to elevate the PVC condensate line.

Build a Concrete Patio Deck Rail - Rear Side
Build a Concrete Patio Deck Rail – Rear Side

Front view of the finished deck rail.

Build a Concrete Patio Deck Rail - Front View
Build a Concrete Patio Deck Rail – Front View

I’ll stain the new deck rail when the weather warms up in the spring.

Thanks for reading!

Bob Jackson

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Bob Jackson
Bob Jackson
Technology product manager by day and a prolific handyman in the evenings and over the weekends. Bob was the founder of the original Handyman How To website and that tradition continues on this site with excellent new handyman content into the future.
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