Composite decking is a long-lasting wood alternative, but it isn't wood. Here are some pro tips for building your composite deck the right way.
Introduction
When Trex composite decking hit the market in the mid-1990s, many of the builders I knew were skeptical. As it turned out, they had good reason. Early efforts to combine sawdust with plastic into durable decking material produced boards that swelled and turned moldy. But today (and two class-action lawsuits later) the composite decking that Trex produces has improved more than enough to satisfy the skeptics.
Trex isn't the only company that manufactures composites, but its products are the most common, according to expert remodeler Josh Rudin. Other brands he cites, including AZEK (TimberTech), Fiberon and MoistureShield, are comparable in quality. I can't tell you from experience how long composite decking actually lasts, since recent versions have been on the market for less than 20 years. But warranties promise 25 to 30 years, and it's a good bet top-quality products can last longer.
Composite decking costs a little more than wood, and working with it is almost like working with wood, with a few key differences. With the help of pros Randy Moe from Decks Unlimited and Bob Januilk and Matt Norden from Precision Decks, this post will walk you through the process of building your own composite deck.
Tools Required
- Chalk line
- Circular saw
- Corded drill
- Cordless drill driver
- Measuring tape
- Miter saw
- Power plane
Materials Required
- Hidden decking fasteners
- One-inch composite fascia
- Polyurethane
- Pre-fab aluminum railing
- Pressure-treated lumber
- Screws and bolts
- Two-inch composite decking
Project step-by-step (12)
Step 1
Avoid a Wavy Deck Surface
Joists tend not to be uniform; some may be slightly wider than others (even 1/8 inch makes a difference), and some may have a noticeable crown. If you lay decking on uneven joists, the result will be a wavy surface. To prevent that, stretch a string across the joists, mark the high spots, and plane them down with a power hand planer. It may seem like a lot of extra trouble, but it pays off with a better-looking deck.
Step 2
Beware of Dark Colors
Composite decking with a dark color absorbs UV radiation and can get very hot in direct sunlight. This makes the deck hard to walk on with bare feet, and in extreme heat, pure PVC boards — which aren’t technically composites but are becoming just as popular — can soften and warp.
To avoid these problems, choose light colors like beige, gray or tan. If you really want a darker deck, opt for a product that has been treated with a reflective coating, such as Trex Transcend or Owens Corning WearDeck. Most major composite manufacturers have a line of heat-resistant decking.
Step 3
Hide the Ends of the Boards
Color isn’t always uniform throughout a board, and this is most obvious at the ends. An easy way to hide the ends is to construct a frame around the perimeter of the deck. Lay the frame flat and miter the corners just as you would a picture frame.
You may need to add extra support around the outside perimeter for the frame, and extra 2X6s fastened directly to the outside of the rim joists work well. Add 1X6 composite fascia boards for a nice finish.
- Pro tip: Top-quality composite decking is capped to keep out moisture, which means the boards are sealed with a waterproof coating. You break that seal when you cut the boards, so to prevent swelling and other problems that dogged early composite products, I always seal cut ends with a dab of polyurethane.
Step 4
Protect the Joists from Rot
Whether you use pressure-treated lumber or rot-resistant species like redwood or cedar for the joists, they are still vulnerable to the weather. The two places where our pros often see rot are on the top edges and between two joists that are sandwiched together.
Spread butyl tape along the top edges of the joists before you install the decking, and your deck will last years longer. Use dark-colored tape because white or silver will be noticeable between the gaps.
Step 5
Space Joists for Adequate Support
Composite decking boards aren’t as rigid as wood and need a lot of support to prevent sagging. For a typical square or rectangular layout, 16-inch spacing is usually adequate. If you install your decking diagonally, reduce the spacing to 12 inches.
The same considerations apply to stairs, which means spacing stringers more closely together than you would for wood stairs and possibly adding one or more extra stringers, depending on the length of the treads.
Before constructing the deck, check the spacing requirements for the product you plan to install because these requirements vary.
Step 6
Use a Splice Board to Avoid Butt Joints
If you have a long deck (24 feet or more), you’ll need to make random butt joints to cover the deck with shorter boards, and each joint can potentially swell and lift. A more elegant way to lay out the deck is to place perpendicular splice boards at strategic locations, eliminating the need for random butts.
You’ll have to install blocking between the joists to support this board, so it’s a little extra trouble. But you’ll more than make that up by avoiding the frustration of trying to splice the decking over joists. If you construct a perimeter frame, the splice board will become part of it, resulting in a cleaner-looking deck overall.
Step 7
Hide the Fasteners
You can drive screws straight into composite decking, just as you do for wood, but each screw penetration is a potential source of swelling and mold. Exposed screws are generally unsightly, and you don’t need them because there’s a better way: use hidden fasteners.
One option is the Cortex concealed fastening system, which includes a countersinking screw bit and a number of plugs that match the composite material. Drill the screw holes, drive the screws and tap in the plugs to fill the holes.
Another option, and the one I prefer, is a hooked bracket system, which requires the use of boards grooved along both edges. Most manufacturers offer grooved boards, but you also cut your own grooves with a table saw. Screw the brackets loosely onto the joists, install the boards by slipping the hooks into the grooves and tighten the screws. This method is super easy and leaves the deck surface completely free of plugs or fasteners.
Step 8
Install Pre-Fab Aluminum Rails
Stair railings are one of the trickiest parts of any deck project. To make things easier, install a preassembled aluminum railing that racks to whatever angle you need. Several manufacturers offer them.
Just measure the distance between the posts, transfer the proper angle and cut to length. If your rails fit into a sleeve, you can cut them with a hacksaw, reciprocating saw or circular saw.
Depending on your design, your rail ends may end up being exposed. If so, you may want to invest in an aluminum blade for your chop saw to make smooth, burr-free crosscuts. Either way, clean up the ends with a file, so you don’t scratch things up during installation.
Step 9
Mix It Up
You don’t have to stick with one type of product, one color or one look for the entire deck. Our pros always mix and match, using composite posts with aluminum rails or composite rails with aluminum spindles.
Don’t be afraid to think outside the box regarding color. You can install perimeter boards in the same color as the railing, choose a post color that’s different from the railing or find a complementary color for your composite deck stairs. You can even have the spindles be a different color than the posts and rails.
Distinctive touches like this put your signature on your work, and the possibilities are endless.
Step 10
Use Railing Connectors
Attaching rails to posts and getting a tight fit can be difficult, even for pros. A slight angle during crosscutting or a mismeasurement of even 1/8 inch can result in an unsightly gap. Since the railing is the first thing people using the deck are likely to see, it can detract from the quality of workmanship on the rest of the deck.
The solution is simple: use railing connectors, such as the ones in this picture supplied by Deckorator. They support the rails from underneath, much like joist hangers do, and they mask any small cutting mistakes you make, so you can work more quickly and breathe easier.
Step 11
Dress Up Ugly Posts
You’ll likely use pressure-treated lumber for your posts, and it isn’t the most attractive building material. You can paint or stain it, but it will still look rougher than the composite material you use for the deck.
Turn those less-than-beautiful posts into a feature by wrapping them in matching composite or PVC boards. You’ll need two 1x6s and two 1X8s for each post. Cut them to length and pin them in place with a trim gun before driving screws to hold them together permanently.
- Pro tip: Our pros avoid material thinner than 3/4-in. because PVC and composites expand and contract more than wood, and it’s hard to keep the seams together using thinner material.
Step 12
Improve the View with Dark, Round Spindles
Light colors are easier to see than dark ones, which is great for a horse fence, but not so good for a deck railing. If you want a less unobstructed view, go with a dark color for your railing spindles.
Using round spindles instead of square ones also helps to preserve the view, and here’s why: When you look at a 1-inch square spindle diagonally, its profile increases by almost 50 percent. A round spindle, on the other hand, looks the same from every viewing angle.
About the Pros
- Josh Rudin is a Certified Restorer and the owner of Phoenix-based ASAP Restoration.
- Randy Moe is the owner of Decks Unlimited, a custom deck company based in Minneapolis/St.Paul MN.
- Bob Januik and Matt Norden are the owners of Precision Decks based in Corcoran, MN.
Originally Published: July 16, 2021
