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Trex Decking Installation Guide

Learn how to build a deck with composites and other rot-resistant materials for beauty and longevity.

composite decking deck joist spacingFamily Handyman
Expert deck builders show you how to install Trex decking like a pro! Get step-by-step instructions (with pictures) & pro tips from our composite deck experts!

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Build decks using composite and other low-upkeep materials

Your deck should be a place to relax, not a painful reminder of those looming weekends you’re going to spend sanding, painting and staining. So if you’re in the planning stages for a new deck, consider alternatives to wood and check out some composite deck designs.

You can build yourself a low-maintenance deck using the same tools as you would a wood deck, and similar techniques. And most parts of a deck are now available in composite material. But there are differences between low-maintenance and wood products. We asked our pros for some tips to help DIYers avoid expensive mistakes.

Don’t know what your deck will look like? Check out this floating, platform deck the Family Handyman built.

Meet Our Experts

We asked Randy Moe from Decks Unlimited, and Bob Januik and Matt Norden from Precision Decks, for some tips on working with low-maintenance deck materials, including trex. Altogether, these guys have built more than 1,000 decks, using every material imaginable. Ten years ago, about half their jobs were wood. Today they install low-maintenance materials on three out of four.

Flatten joists to avoid a wavy deck

Decking supports: Planning a deck joist

Stretch a chalk line across the joists to find high spots and plane them down.

Most PVC and composite products aren’t as rigid as wood, so they don’t bridge imperfections in the framing as well. If some of your joists are higher than others, you might end up with a wavy surface. Our pros stretch a string across the deck joists to detect high spots and then plane them down with a power hand planer. This might seem like a pain, but it takes less than an hour and pays off with a better-looking deck.

Beware of dark colors when choosing composites

Boards with dark colors can get blistering hot when the sun is beating down on them. If you like to go barefoot, consider a lighter color.

How to Install Hidden Deck Fasteners

Hide composite ends

Mitered joint

Hide composite ends by mitering joints around the deck perimeter. Add extra joists for support as needed.

Many PVC and trex composite decking products are not the same color all the way through, so you’ll want to cover the ends. One solution is to “picture frame” the deck by installing trex deck boards around the perimeter. A picture frame creates a professional look but does require some additional framing. One way to support the perimeter boards is to add an extra joist 5-1/2 in. away from the outside joist and then install a 2×6 on its side between the two joists.

Click here for some pro-tips on tight miter joints.

Protect joists from rot

Apply waterproof tape to decking supports

Lay butyl tape over the joist tops to help prevent rot.

Pressure-treated lumber is rot-resistant, not rot-proof. Two places our pros often see deterioration are along the top edge, where the decking traps moisture, and in between two joists that have been sandwiched together. Rolling butyl tape over the top of the joists will add years to your deck’s framing. Choose a dark-colored tape; shiny silver and white are noticeable between the gaps. A 4 in. x 75 ft. roll will cost you about $20 at a home center.

Check deck joist spacing

If you’re planning to replace old wood decking with PVC or composite, measure the deck joist spacing first. Most deck joists are centered 16 in. apart, which is the maximum deck joist spacing for most low-maintenance decking. If you plan to install your decking at a 45-degree angle, your joists may need to be 12 in. apart. You may also have to install more stair stringers. Check your product specs, and talk to your local building official before you buy.

Avoid random splices

Splice long runs

Use splice boards to eliminate random splices in long runs.

If your deck is 24 ft. long, don’t use random-length boards and butt-joint them together. Install a splice board to create two 12 ft. x 12 ft. spaces instead. Your deck will look better and you’ll avoid the frustration of trying to splice the decking over joists. A splice board will also require extra framing. Do it the same way you would for the perimeter boards (one extra joist and a 2×6 on its side between the outside joist and the extra joist).

Hide the screws

Hidden fastener system

Special screws, a screw driver bit and composite plugs make the fasteners invisible.

When it comes to fastening PVC or composite decking, all three of our pros like the Cortex concealed fastening system. You just countersink the screws using the special bit included with the kit, and hammer in a plug that’s made of the exact same material as the decking. Screw holes virtually disappear, and damaged boards are easy to remove if you have to. A box of 350 costs about $80 at Home Depot. It’s features like this that make composite deck designs really look polished.

Stair rails made simple

Preassembled aluminum railing

A preassembled railing simplifies the long, tedious process or rail building.

Stair railing

You can “rack” the same railing to the angle that fits your stairway.

Stair railings are one of the trickiest parts of any deck project. Some aluminum manufacturers offer a preassembled railing that racks to whatever angle you need. 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. If your rail ends will be exposed, you may want to invest in an aluminum blade for your chop saw. Either way, clean up the ends with a file so you don’t scratch things up during installation.

Learn more about deck railing repair here.

Mix and match

Deck/railing material options

You can mix composites with aluminum and other materials from various manufacturers. You can even use several composite colors.

You don’t have to stick with one type of product or one look for the entire deck. Our pros mix and match all the time: composite posts with aluminum rails, composite rails with aluminum spindles. And don’t be afraid to think outside the box when it comes to color.

You can install perimeter boards the same color as the railing. Choose a post color that’s different from the railing. Find a complementary color for your composite deck stairs. Have the spindles be a different color than the posts and rails. The possibilities are endless.

Connectors make railings easier

Railing/post connector

Special connectors make difficult joints easier and stronger.

Creating a tight fit between a composite deck posts and a rail is difficult—even pros struggle with it. Railing connectors make it easy. This connector, made by Deckorator, is screwed onto the end of the rail before being attached to the composite deck posts. It comes in five colors. You can buy these connectors from the same place you get your decking.

Dress up ugly posts

Wrap a wooden post

Wrap a wooden post with PVC to improve appearance.

If your deck is more than a couple of feet off the ground, you may want to wrap the posts in PVC to match the rest of the deck. You’ll need two 1x6s and two 1x8s for each post. Our pros avoid material thinner than 3/4 in. because PVC expands and contracts more than wood, and it’s hard to keep the seams together using thinner material. Pin the boards in place with a trim gun before screwing them together.

Dark, round spindles improve the view

Dark, round spindles

Dark spindles are less distracting and allow a more unobstructed view.

White spindles

White spindles tend to block the view.

Do you know why horse fences are usually white? It’s because dark ones are harder for horses to see. The same principle applies to deck railings and people. If you want an unobstructed view, dark spindles are the way to go. And round is better than square. A 3/4 in.-diameter round spindle stays 3/4 in. no matter what direction it’s viewed from, but a 3/4 in. square spindle grows to more than an inch when you view it at an angle.

Required Tools for this Deck Installation Project

Have the necessary tools for this DIY project lined up before you start—you’ll save time and frustration.

  • Chalk line
  • Circular saw
  • Corded drill
  • Drill/driver - cordless
  • Miter saw
  • Power plane
You’ll also need other tools for deck building.