Installing Trex is very doable, and the boards go down faster and cleaner than wood, especially with hidden fasteners that leave no screw heads on top. But the strength of the deck, and how long it lasts, comes from the part you never see: the framing under the boards. Get that right, and the surface is almost the easy part.
This guide walks the whole build from the top: plan and permit, frame, lay the boards, and finish. Along the way, it covers the Trex-specific rules that matter, and gives you an honest read on which parts are DIY-friendly and which are worth handing to a pro.
We build these across Indianapolis, so we will flag the two local steps that trip people up: frost-depth footings and permits. One note before you start. This is an overview, not a replacement for Trex’s official installation instructions or your local building code. Follow both, and get the required inspections.
Before You Start: Plan, Permit, and Measure
Most of the mistakes we see happen before a single board goes down. Spend the time here, and the build goes smoothly.
- Finalize the design. Shape, board pattern, and railing all change the framing and the material list, so lock in your deck design before you order anything.
- Pull a permit. Most decks in Indianapolis need one. The city requires an Improvement Location Permit plus a structural permit for elevated decks, and Marion County requires contractors to be locally licensed. Check before you dig.
- Measure and order. Calculate your square footage and board lengths, then add about 10 percent for cuts and waste, so the material order comes in on budget.
- Gather tools and materials. You will want a circular saw with a fine-tooth composite blade, a drill and driver, hidden fasteners or composite screws and plugs, a chalk line, a level, and a tape measure.
The Build at a Glance
Here is the whole sequence in one view. The rest of the guide walks through each stage.
Framing: The Part That Matters Most
Composite is more flexible than wood, so the framing has to be right or the finished deck feels bouncy and can sag. This is also the part most tied to safety and code.
- Footings below the frost line. In central Indiana, that means digging roughly 30 to 36 inches down, into undisturbed soil, so the ground cannot heave the deck in winter. Ground-level or floating decks may skip deep footings, but confirm with your building department.
- A flashed ledger board. On an attached deck, the ledger bolts to the house and must be flashed to keep water out of the wall. This one connection causes more deck failures than any other, so do it carefully or hire it out.
- Joists at the right spacing. Set joists 16 inches on center for straight boards and 12 inches for a 45-degree diagonal, and make sure every board spans at least three joists. For the full rundown, see the exact spacing and fastener specs.
- Solid substructure overall. Posts, beams, and blocking all carry real load, since composite is heavier than wood. If you want the framing basics start to finish, our general deck-building walkthrough covers them.
If you are resurfacing an old deck, you can often reuse a sound frame, but only if it meets these composite spacing rules. Many older decks are framed at 24 inches on center, which is too wide for Trex, so you would add a joist between each existing one first.
Laying the Boards
With the frame right, the boards go quickly. The method depends on whether your boards are grooved or square edge.
- Start straight. Snap a chalk line and set your first board dead straight, usually against the house or along the outer edge. Everything after keys off that first row, so take your time here.
- Grooved boards, hidden clips. Use start clips to hold the outer edge, then drop a clip into the groove between boards, screw it to each joist, and slide the next board on. The clips self-space the gap, so the spacing comes out even without measuring.
- Square-edge boards, screws and plugs. For borders, stairs, and the perimeter, face-screw the board with composite deck screws and cap each screw with a color-matched plug. Never use plain exterior wood screws, which mushroom the board around the head.
- Mind the gaps and overhang. Leave about 3/16 inch between boards and a wider end gap in cold weather. Boards can overhang the rim by an inch or two, or run flush if you plan to add a border or fascia.
Finishing: Borders, Fascia, Stairs, Railing, and Lighting
The finishing details are what separate a deck that looks built by a pro from one that looks like a weekend project.
- Picture-frame border. A border board frames the deck and hides the cut ends, but the seams need blocking underneath for support.
- Fascia. Wider fascia boards wrap the exposed rim joist and stair risers for a clean, finished edge.
- Stairs. Stair stringers sit 12 inches on center or closer, sometimes 9 inches, and treads should land on at least four stringers.
- Railing and guardrails. Any deck more than 30 inches above grade needs a guardrail, typically at least 36 inches tall with balusters no more than 4 inches apart. Railing posts get through-bolted, not just screwed.
- Lighting. Low-voltage LED post, rail, and stair lights are easiest to run before the railing is fully buttoned up.
Replacing or Resurfacing an Old Deck With Trex
Swapping tired wood boards for Trex on an existing frame is a popular project, and it can save money, but it comes with a checklist. Confirm the frame is sound and not rotted, then verify it meets composite spacing, adding joists if it is framed at 24 inches on center. Check that the ledger and its flashing are still solid and the footings have not shifted. If the old structure is questionable, it is worth rebuilding the frame rather than putting new boards on a failing base. Trex needs proper joist support, so you cannot simply lay it on bare ground or an old concrete slab without a suitable substructure.
DIY or Hire a Pro?
Laying the boards is genuinely DIY-friendly, and a handy homeowner can do a great job on the surface. The riskier work is everything underneath and around it: sizing and pouring frost-depth footings, flashing the ledger, meeting code, and building safe stairs and railings. Those are the parts where a mistake gets expensive or dangerous, and where a pro earns their fee.
- A fair split. Many homeowners hire out the framing, footings, and permits, then install the boards themselves. If you are weighing that against a full professional build, what the project will cost lays out both paths.
- Know your limits. If the deck is elevated, attaches to the house, or involves stairs, leaning on a licensed local builder is the safe call.
Frequently Asked Questions
How is Trex decking installed?
Grooved boards install with hidden clips that seat in the side grooves and screw down to the joists, leaving no visible screws. Square-edge boards are face-screwed with composite screws and capped with color-matched plugs.
Can you screw Trex decking down?
Yes. Square-edge boards are meant to be face-screwed with composite deck screws, then plugged. Just never use standard exterior wood screws, which push the material up and mushroom the surface.
How do you start installing Trex with hidden fasteners?
Snap a chalk line and set the first board perfectly straight, held by start clips at the outer edge. Then work across the deck: drop a clip in the groove, screw it to the joist, and slide the next board on.
What joist spacing does a Trex install need?
16 inches on center for straight boards and 12 inches for diagonal, with every board spanning at least three joists. If an old frame is 24 inches on center, add a joist between each one before you install.
Can you install Trex over an existing deck?
Only if the frame is sound and meets composite spacing. Replace the boards, confirm the ledger, flashing, and footings are still good, and add joists if the spacing is too wide. Trex needs real joist support, not bare ground or a slab.
How hard is it to install Trex yourself?
The boards are the easy part and well within reach for a confident DIYer. The framing, ledger flashing, footings, permits, and stairs are the hard and safety-critical parts, and those are often worth hiring out.
The Bottom Line
Installing Trex comes down to one idea: the boards are quick, and the framing is where the real work and the real risk live. Get the footings deep enough, flash the ledger, set the joists to 16 or 12 inches on center, and the surface goes down fast with hidden clips.
Decide early which parts you will take on. Laying boards is a satisfying DIY job. Footings, the ledger connection, code, and stairs are the places to bring in a pro if you have any doubt.
Around Indianapolis, the two steps people underestimate are frost-depth footings and permits. Handle those correctly, pass your inspections, and you end up with a deck that stays flat, solid, and code-compliant for decades.