Pressure-Treated vs Cedar vs Composite: Choosing Deck Boards
Pressure-treated, cedar, and composite deck boards compared — durability class, joist spacing, fastening, maintenance cycle, heat, and cost.
Updated August 20, 2026
Deck boards rot, split, or fade their way to replacement, and the three main choices each buy longevity a different way: pressure-treated pine is cheap wood made durable by infused preservative, cedar is wood born durable in its heartwood extractives, and composite is not quite wood at all — a wood-flour-and-polymer extrusion whose weathering is governed by an ICC-ES evaluation report instead of a grading stamp.
Dimensionally they agree more than they differ: the standard deck board dresses (or extrudes) to about 5-1/2 inches wide and gets laid with roughly a 1/4-inch drainage gap, and all three families land on the familiar 12/16/24-inch joist grid — those are the same width, gap, and spacing presets the decking quantity calculator uses, mapped here rather than retyped. The consequential differences are in the rows a takeoff never shows: what each surface demands every year, how hot it gets barefoot, and what the fifteenth summer looks like.
Price and maintenance run in opposite directions across the trio. Treated pine is half the money and all of the upkeep; composite is double the money and nearly none of the upkeep; cedar sits between, trading some of each for being genuinely beautiful wood. The use cases below pick per situation rather than crowning one.
Side by Side
| Spec | Pressure-treated pine | Western red cedar | Composite |
|---|---|---|---|
| Material & durability basis | Southern pine infused with copper-based preservative; rated by AWPA U1 use category (UC3B decking above ground; UC4A ground contact) | Naturally durable heartwood (thujaplicin extractives); durability is a property of heartwood grades, not sapwood | Wood flour + polyethylene/PVC extrusion; performance established product-by-product in ICC-ES evaluation reports |
| Standard board width & drainage gapWidth and gap mapped from the decking-quantity calculator’s presets; treated boards are often installed tight-butted wet because they shrink to the gap. | 5-1/2 in actual (nominal 6 in); ≈1/4 in side gap once dry | 5-1/2 in actual (nominal 6 in); ≈1/4 in side gap | 5-1/2 in typical extrusion; ESR mandates edge and end gapping per the maker's instructions — commonly ≈1/4 in side, plus end gaps for thermal movement |
| Max joist spacing, boards perpendicularAll three families land on the calculator’s 12/16/24 grid; diagonal decking always steps one grid tighter. | 16″ o.c. for 5/4 boards; 24″ o.c. for full 2-in boards | 16″ o.c. for 5/4 boards; 24″ o.c. for 2-in boards (WRCLA spans) | Per the product’s ICC-ES report — representative: 16″ o.c. perpendicular, 12″ at 45° diagonal (ESR-3168 Table 1) |
| Fastening options | Nails or (better) coated/stainless deck screws; fastener corrosion rating must match the preservative | Stainless fasteners to prevent tannin staining; face-screw or hidden-clip systems on premium grades | Hidden edge clips on grooved boards or the listed composite deck screws on square-edge; the fastener system is specified in the ESR |
| Maintenance cycle | Highest: re-stain or reseal on a 1–3 year rhythm, plus splinter and cup patrol; skipping it halves the deck’s good years | Moderate: annual wash and periodic oil/stain to keep color; left alone it silvers gracefully but checks | Lowest: soap-and-water cleaning; no sealing ever — mold on shaded boards is the one recurring chore |
| Surface heat & splinter behavior | Moderate heat; splinters and raised grain arrive with weathering | Coolest underfoot of the three and naturally splinter-mild | Runs hottest in full sun — dark colors can be barefoot-hostile; zero splinters by construction |
| Cost drivers | Cheapest board and the budget baseline; add the recurring stain/sealer and weekend labor to compare honestly | Mid-priced and regionally variable (cheap in the Northwest, premium elsewhere); clear grades price far above knotty | Highest upfront by roughly 2–3× treated pine; the ledger balances only over years of skipped refinishing |
Which One for the Job
Budget ground-level deck
Pressure-treated pine
Close to grade, boards live in splash and shade — durability duty that AWPA use categories cover explicitly and cheaply. At half the material cost of the alternatives, treated pine leaves budget for the framing and footings that actually determine the deck’s life, and a ground-hugging platform is the easiest surface to re-stain on schedule.
Low-maintenance family deck
Composite
A used-daily deck is exactly where the no-sanding, no-staining, no-splinter ledger pays: the upfront premium amortizes across every refinishing weekend that never happens. Pick a light color if it bakes in full sun, respect the report’s joist spacing and gapping, and the surface is a wash-and-use appliance for decades.
Naturally rot-resistant look with real wood
Western red cedar
Cedar is the option that is both genuinely durable and genuinely wood — real grain underfoot, the coolest surface of the three, and heartwood that resists decay without infused chemistry. It asks for stainless fasteners and periodic finish in exchange, and the durability promise belongs to heartwood grades, so buy the grade, not just the species.
Deck framing under any of the three surfaces
Pressure-treated pine
Whatever walks on top, the joists, beams, and posts underneath are treated lumber — composite makes no structural members and cedar framing prices absurdly. Match the use category to the exposure (ground contact where it touches or nears grade) and match fastener corrosion ratings to the treatment, then choose the wear surface on its own merits.
Frequently Asked Questions
How big a gap should deck boards get between each other?
About a 1/4-inch side gap in service for drainage and debris clearance — the same default the decking calculator carries. The nuance is when the gap is created: kiln-dried and composite boards are installed at the gap, while wet treated lumber is often butted tight and left to shrink to it. Composites additionally require end-to-end gaps per their report, because polymer boards move with temperature, not moisture.
Why does composite decking have its own joist-spacing rules?
Because it is a listed product, not graded lumber: a composite board’s stiffness comes from its specific polymer recipe and profile, so allowable spans are established by testing and published in that product’s ICC-ES evaluation report rather than in a species span table. Representative reports land at 16 inches on center perpendicular and 12 inches diagonal, but the report for the actual product — not a habit — governs.
Does cedar decking still need to be sealed if it resists rot?
For decay, no — heartwood durability is in the wood itself. For appearance and surface condition, yes: unfinished cedar weathers to silver-gray and develops checking as UV and moisture cycles work the surface. A penetrating oil or semi-transparent stain every few seasons keeps the color and slows checking. The other non-negotiable is stainless fasteners, since cedar’s tannins streak black around ordinary hardware.
Is treated-pine decking safe for vegetable-garden planters and play areas?
Modern residential treatments (ACQ and copper azole, which replaced CCA for consumer lumber in 2003) are copper-based and approved for residential contact, including play structures. Sensible practice remains: let boards dry before use, never burn offcuts, wear a mask when cutting, and line planting beds if direct soil-to-food contact is a concern. The bigger practical hazard is fastener corrosion — the chemistry that protects the wood attacks bare steel.
Try the Calculators
Sources
- AWPA U1 — Use Category System for preservative-treated wood (UC3B above-ground decking, UC4A ground contact)
- WRCLA (Western Red Cedar Lumber Association) published decking data — spans for 5/4 and 2-in cedar decking, finishing and fastener guidance
- ICC-ES ESR-3168 (Trex Transcend/Select, reissued Feb 2023), representative composite evaluation report — Table 1 spans (16″ o.c. perpendicular, 12″ at 45°), gapping and fastening requirements
- Decking-quantity calculator presets (board width, gap, joist-spacing grid) — the mapped dimensional cells