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How to Build a Deck: Composite Decking and Railings

Composite deck materials add sophistication and durability to any deck. Here's how to install composite decking and railings.

See the complete deck project from design to finishing touches at Lowes.com/BuildaDeck.

Before You Begin

You'll need a solid frame for any type of decking. This deck has a frame made of pressure-treated lumber. If you need help with framing and setting the posts, see How to Build a Deck: Post Holes and Framing.

If you choose to install wood decking, you can find step-by-step instructions in How to Build a Deck: Wood Decking and Railings.

Good to Know

Follow all local building codes.

Mounting the Railing Posts

For composite decks, mount the posts to the inside of the joists.

Step 1

Steps to Determine Railing Post Spacing.

Start by determining the number of posts you need and the post spacing. You should have posts by the house, at outer corners and at the top of the stairs. Measure the distance between two corner posts and divide by the distance allowed between posts. Round up to the nearest whole number, then subtract 1.

15 feet ÷ 5 feet = 3

3 - 1= 2 posts in between

Make sure the posts are evenly spaced. If one lines up over a joist, you can reposition it slightly.

Good to Know

Most codes permit a maximum post spacing of 6 feet.

Step 2

Cut the Railing Posts to Length.

Cut the posts to length according to your plan and local codes. The bottom ends of the posts will be flush with the bottom edges of the rim and end joists.

Step 3

Attach Bracing for Posts on the End Joists.

This deck has deck anchors attached to the joists, which makes for a stronger railing.

Along the end joists, use deck screws to attach extra bracing between the floor joists and end joists to mount the anchors. Cut the bracing from the same 2 x lumber you used for the joists (for this deck 2 x 8 lumber).

Good to Know

Your local code may specify a method of post installation.

Step 4

Attach the Post with Screws.

Begin installing posts along an end joist. Screw a post in place, making sure it's plumb and extends to the bottom of the joist.

Good to Know

You can use clamps to keep the posts in position while you fasten them to the deck.

Step 5

Mark the Bolt Hole for the Anchor.

Mark the joist at the center of the post about 2 inches from the top and 2 inches from the bottom.

Step 6

Drill Two Bolt Holes for Each Post.

At the marks, drill two bolt holes through the end joist and post.

Step 7

Install the Carriage Bolts.

Insert the carriage bolt in the top hole, place the anchor and tighten the nut and washer.

Step 8

Screw in the Bracket.

Attach the anchor to the bracing with screws.

Step 9

Secure a Second Carriage Bolt Through the Joist and Post.

Secure a second bolt through the bottom hole. Each post should have two carriage bolts, but will only need one anchor.

Step 10

Install a Second Anchor at the Back of the Bracing.

Attach an anchor on the back of the bracing for added strength.

Step 11

Install Bracing Around Corner Posts.

Continue installing posts. For posts in the corners, add bracing around the post and secure it with anchors. Again, cut the bracing from the same material you used for the joists (in this case 2 x 8 lumber).

Step 12

Add Bracing Behind Posts on the Rim Joist.

Along the rim joist, add similar bracing behind the posts with screws and corner brackets, then secure the posts with carriage bolts.

Installing the Decking

Once all the posts are secured you can install the decking. For a cleaner look, use hidden deck clips and grooved composite boards. If you deck will have parting boards running down the middle, install decking on either side of the bracing you installed to support them. You'll trim the decking before installing the parting boards.

Good to Know

The hidden clips set a drainage gap between the boards.

Step 1

Install Start Stop Clips for the First Board.

Starting near the house side of the deck, use screws to secure the start / stop clips flush with the rim joist, spaced about every 16 inches.

Step 2

Install the First Board.

Set your first board down, and push the groove over the clip prongs.

Step 3

Install Clips for the Second Board.

Next, at every joist, insert a clip prong fully into the board's groove and secure with screws.

Step 4

Install the Second Board.

Line up the grooves on the next board with the prongs, and push the board tightly into place. Overhang the boards by a couple of inches at the end joists. You'll trim them later. Continue installing the boards. Use a jigsaw to cut the decking and work around the posts as needed. You can make the cutouts a bit wide to help fit the boards in place — you'll cover the gaps later with post skirts.

Good to Know

You'll need someone to assist you with installation of long deck boards.

Step 5

Attach the Last Board with Composite Decking Screws.

The last board might not need to be full width. Rip it — cut along the length of the board — to fit if necessary. If you're installing skirting, leave a 1-1/4-inch overhang. Set the board in place and attach with composite decking screws. Later you can cover the cut edge with a fascia board.

Good to Know

If you're not installing skirting, you can cut the decking flush with the joists. On the last deck board, you’ll have to rip it to fit and then cut a groove into the board with a router. To secure the board, place the start / stop clips in the groove and attach with screws.

Step 6

Snap a Chalk Line to Trim the Boards to Length.

To trim the deck boards to length, snap a chalk line along the end joist and cut along the line with a circular saw. Leave a 1-1/4-inch overhang if you're installing skirting.

Good to Know

A saw cutting guide helps you make clean, straight cuts.

Step 7

Trim the Decking to Fit the Parting Boards.

At the center of the deck, cut the decking to fit the parting boards.

Step 8

Install the Parting Boards.

Secure the parting boards in place with composite decking screws. Use a screw to set a drainage gap.

Installing the Railings

Step 1

Slide on the post sleeves. Cut them to height if necessary.

Step 2

Glue Post Collars with PVC Cement.

Glue post sleeve collars in place with PVC cement. Follow the package instructions.

Step 3

Measure Between Posts and Mark the Bottom Rail.

Measure the distance between posts and mark both ends of each bottom rail 1/4-inch shorter, keeping the baluster hole spacing even between the marks.

Step 4

Mark the Top Rail.

Measure and mark the top rail in the same way.

Step 5

Cut the Rails to Length.

Cut the rails to length.

Step 6

Glue a Crush Block to the Underside of the Bottom Rail.

Use PVC cement to secure a crush block centered on the underside of each bottom rail. Allow the glue to cure.

Step 7

Trace the Bottom Bracket.

Slide the brackets and flanges onto a bottom rail. Hold the rail in place, trace the brackets on the posts and then remove the rail.

Good to Know

You can temporarily place another crush block under the bottom rail near the post to support the bottom rail at the correct height.

Step 8

Mark Flange Holes.

Reposition the brackets and flanges on a post and mark the holes. Drill pilot holes and secure the flanges with screws. Follow the same procedure on the other post.

Step 9

Slide the brackets back onto the rails and lock the rails in place between the posts.

Step 10

Install the Top Brackets.

Put the end balusters in place as guides and set the top rail in place. Mark the bracket location and install the flanges as you did on the bottom rail.

Step 11

Lock the Top Rail in Place.

Insert all the balusters and then lock the top rail in place. Attach post caps with PVC adhesive.

Step 12

Install the rest of the railings.

Caution

Always follow the manufacturer's recommendations for fasteners and structural hardware.

Working with Pressure-Treated Lumber

Guidelines

  • Use fasteners and hardware labeled for treated lumber — stainless-steel or hot-dipped, galvanized screws.
  • If the lumber is wet — it typically is when delivered from the store — butt it together tightly when building. Pressure-treated wood shrinks as it dries.
  • Drill pilot holes in the ends of boards to prevent splitting when you nail or screw them together.
  • Use wood rated for ground contact when necessary for the project.

 

Safety

  • Wear a dust mask and eye protection when handling or cutting wood.
  • Wash your hands after working with treated wood.
  • Dispose of sawdust and waste according to local regulations.
  • Don't burn pressure-treated wood.
  • Don't use pressure-treated wood as mulch.

Read more about pressure-treated lumber and wood preservatives on the EPA website:

Overview of Wood Preservative Chemicals.

Next Steps

It's time to attach the stairs. See How to Build a Deck: Composite Stairs and Stair Railings.

Watch the complete deck series at Lowes.com/BuildaDeck.