A Trex deck lives or dies on the parts you never see. The color and the grain get all the attention, but the dimensions, the gaps, and the hardware underneath are what make a deck feel rock solid for twenty-five years instead of bouncy and loose in five. Get these details right, and you stop thinking about them. Get them wrong, and you feel it every time you cross the boards.
This guide covers the numbers that matter: how wide and thick the boards are, what lengths they come in, how much room to leave between them, how far apart your joists can sit, and exactly which clips, plugs, and screws hold it all together. No jargon, just the specs and what they mean for your build.
We build these decks on Indianapolis homes, so we will also flag where our weather changes the math. Hot summer sun and hard winter freeze-thaw both push on a composite deck, and a couple of these numbers shift because of it.
The Quick Specs, at a Glance
If you only need the headline numbers, here they are. The rest of the guide explains where each one comes from and when it changes.
| Spec | Trex standard |
|---|---|
| Board width | 5.5 in (all main lines) |
| Board thickness | About 0.8 to 1 in, varies by line |
| Board lengths | 12, 16, and 20 ft |
| Side gap between boards | About 3/16 in (hidden clips self-space) |
| Joist spacing, straight boards | 16 in on center (maximum) |
| Joist spacing, 45-degree diagonal | 12 in on center |
| Minimum support | Every board spans at least 3 joists |
| Board weight | About 1.5 to 2.5 lb per linear foot |
Source: Trex product specifications and installation guidelines, 2026. Figures cover Trex’s main residential decking lines.
Trex Board Dimensions: Width, Thickness, Length, and Weight
Every standard Trex board is 5.5 inches wide. That number does not change from one line to the next, which is why boards from different collections line up cleanly side by side. What does change is the thickness. Trex’s entry boards run a little thinner than its premium boards, so there is one rule worth burning into memory: never mix two different lines on the same deck surface. Even a small height difference between boards becomes a trip hazard and an eyesore. Pick one line and stay with it across the field.
| Profile | Actual size (approx.) | Best used for |
|---|---|---|
| Standard board (1×6) | 0.8 to 0.94 in x 5.5 in | The main deck surface |
| Heavy board (2×6) | About 1.3 in x 5.5 in | Stairs, structural spans, picture-frame borders |
| Fascia (1×8) | 0.56 in x 7.25 in | Wrapping the frame and short risers |
| Fascia (1×12) | 0.56 in x 11.375 in | Tall risers and skirting |
Source: Trex Select, Transcend, and Fascia product cut sheets, 2026. Thickness varies slightly by collection.
Boards come in three lengths: 12, 16, and 20 feet. Longer boards mean fewer end seams across a big deck and a cleaner look, while shorter boards are easier to handle and better for stairs and tight spots. Most decks use a mix. If you are still deciding between board types and profiles, our weighing your deck board options rundown walks through the trade-offs.
Composite is heavier than wood, and it is worth planning for. Trex boards weigh roughly 1.5 to 2.5 pounds per linear foot, so a single 16-foot board runs about 25 to 40 pounds depending on the line. That is a two-person carry on a hot day, and more to the point, it is real weight your framing has to carry. A frame sized for lightweight lumber is not automatically sized for composite.
Board Spacing and Gaps
Composite decking expands and contracts a little as the temperature swings, so the gaps between boards are not a suggestion. They give the boards room to move, and they let rain drain through instead of pooling on top. Here is where the space goes.
- Side to side. About 3/16 inch between boards. If you use hidden clips, the clips set this gap for you automatically.
- End to end. Where two board ends meet on a joist, leave 1/8 to 3/16 inch. Go a touch wider in cold weather, since the boards are already contracted and will grow in summer.
- From walls and posts. Keep boards 1/4 to 1/2 inch away from any solid object so they can move without binding.
- Near water. Widen the gap to about 3/8 inch next to a pool or water feature.
This is one spot where Indianapolis weather earns a mention. Our summers run hot and our winters bite, so the boards see a real range of movement across the year. When we install on a cold day, we leave slightly larger end gaps because the boards will expand as they warm. Hidden fasteners take the guesswork out by holding a consistent gap no matter the season.
Joist Spacing and Framing Requirements
The frame decides how the finished deck feels underfoot. Composite is more flexible than wood, so it needs joists set closer together than you might use for a lumber deck. Space them too far apart, and the deck feels bouncy, the surface can sag, and you void the Trex warranty. These are the limits Trex sets.
- Straight boards. 16 inches on center is the maximum for a standard perpendicular layout.
- Diagonal boards. Running the boards at a 45-degree angle puts more stress on them, so the joists must come in to 12 inches on center.
- 2×6 boards. The thicker 2×6 profile can span wider, up to 24 inches on center in residential use under normal loads.
- Stairs. Stair stringers need to sit 12 inches on center or closer, sometimes 9 inches, and treads should land on at least four stringers.
- Heavy loads. Hot tubs, large planters, and built-in features need tighter framing and often bigger joists. Check with your local building office for those.
One rule cuts across all of these: every Trex board has to span at least three joists. A board resting on only two supports flexes too much in the middle.
If you want to see how the framing fits into the whole project, from footings to the final board, here is how a Trex deck gets built. Trex also makes a steel framing system and matching steel-framing clips, if you want a substructure that will not rot, twist, or need replacing before the boards do.
Central Indiana adds one framing detail that has nothing to do with the boards and everything to do with the ground: frost. Footings need to sit below the local frost line so the deck does not heave when the soil freezes and thaws. Your township or the Marion County building department can confirm the required depth for your address before you dig.
Trex Hidden Fasteners: Clips, Plugs, and Screws
Trex sells its own fastening system, the Trex Hideaway Collection, and it gives you three ways to attach boards. Which one you use depends on the edge of the board and where it sits on the deck. Most decks use all three in different spots.
Hidden clips for grooved boards
Grooved-edge boards have a channel milled into each side. A small clip drops into the groove between two boards and screws down into the joist, so nothing shows on the walking surface. Trex’s Universal Hidden Fastener is a glass-filled nylon clip with a preset stainless steel screw, and one 90-piece pack covers about 50 square feet at 16-inch joist spacing. The clips also self-space the boards, which is why the side gap comes out even without measuring. For a steel substructure, Trex makes a steel-framing version of the same clip.
Color-match plugs for square-edge boards
Square-edge boards have no groove, so they get screwed down from the top and then capped. Trex Hideaway plugs are made from the same material and color mix as the decking itself, so they nearly disappear once tapped in. Square edge is the go-to for borders, stair treads, and the deck perimeter, anywhere a grooved profile will not work. Because the plugs match the board, your color choice matters here too. If you have not locked that in yet, browse the full range of Trex board colors before you order hardware.
Composite deck screws
For face-screwing without plugs, or for trim and repairs, use screws made for composite. They are designed to drive flush and pull the material down cleanly. Never reach for plain exterior wood screws. They push the composite up around the head and leave a raised, mushroomed ring on the board. Fascia gets its own color-matched screws and plugs so the edge looks as finished as the top.
Finishing Touches: Fascia, Trim, Post Caps, and Accessories
Boards and fasteners build the deck, but a handful of accessories are what make it look finished and last longer. These are the pieces that wrap the raw edges, protect the frame, and put the space under the deck to work.
- Fascia boards. Wider, thinner boards (1×8 and 1×12) that wrap the exposed frame and cover stair risers for a clean, built-in look.
- Post caps and edge trim. Small finishing pieces that cap railing posts and tidy up exposed board ends.
- Joist and beam tape. A butyl tape laid over the top of the framing before the boards go down. It seals around each fastener and shields the wood frame from trapped water, which is cheap insurance in a freeze-thaw climate like ours.
- Under-deck drainage. Trex RainEscape and similar systems run troughs between the joists to carry rain away, turning the space beneath a raised deck into dry, usable storage or a covered patio. It installs on standard 12- and 16-inch joist spacing.
- Deck gates. Matching gates for stair tops, pool areas, and pets.
For the full menu of railings, lighting, and other add-ons, see the accessories that complete your build.
Cutting and Working With Trex
Trex cuts, drills, and routs a lot like wood, with a couple of composite-specific habits worth adopting.
- Use a fine-tooth blade. A carbide blade with more teeth leaves a cleaner edge on composite than a coarse framing blade.
- Predrill near the ends. When you face-screw close to a board end, a pilot hole keeps the board from mushrooming or splitting.
- Sealing cut ends is optional. Cut ends do not need sealing for strength, though some builders dress them for a uniform look.
- Glue is a helper, not a fastener. Composite adhesive can lock down trim and small pieces, but it never replaces clips or screws on the deck field.
Frequently Asked Questions
How thick is Trex decking?
Standard boards run about 0.8 to 1 inch thick, depending on the line, and every board is 5.5 inches wide. Trex also makes a thicker 2×6 profile for stairs and structural spots.
How much space do you leave between Trex boards?
About 3/16 inch side to side and 1/8 to 3/16 inch where two board ends meet on a joist. Hidden clips self-space the boards to a consistent gap, and it is smart to leave a little more room when you install in cold weather.
What joist spacing does Trex require?
16 inches on center for straight boards and 12 inches for a 45-degree diagonal layout. Stair stringers go 12 inches or closer, and every board must span at least three joists. Framing wider than the spec voids the warranty.
What lengths does Trex decking come in?
Standard boards come in 12, 16, and 20-foot lengths. Longer boards leave fewer seams on a large deck, while shorter ones are easier to handle and work well for stairs.
How much does Trex decking weigh?
Roughly 1.5 to 2.5 pounds per linear foot, so a 16-foot board weighs about 25 to 40 pounds. It is noticeably heavier than treated wood, so your framing needs to be sized for the extra load.
What screws or fasteners work with Trex?
Hidden clips for grooved boards, and composite deck screws with color-matched plugs for square-edge boards. Never use plain exterior wood screws, which mushroom the board surface around the head.
The Bottom Line
Dimensions, gaps, joist spacing, and fasteners are the unglamorous half of a Trex deck, and they are exactly the half that decides whether it feels solid in year twenty or starts to sag in year five. Boards are 5.5 inches wide and come in 12, 16, and 20-foot lengths. Framing tops out at 16 inches on center for straight boards and 12 for diagonal. Leave the gaps, and match your fasteners to your board edge.
The simplest way to get it right is to decide the board edge first. Grooved boards want hidden clips, square-edge boards want color-matched plugs, and everything gets composite screws rather than wood screws. Nail those choices and the rest of the hardware falls into place.
On our Indianapolis builds, this is the part of the job we slow down for the most, because it is the part nobody sees and the part that never gets a second chance once the boards are down. Do it carefully once, and the deck rewards you with decades of not thinking about it.