Pressure-treated lumber is the standard choice for most deck framing and deck boards, while naturally durable woods like cedar only qualify under specific code conditions.
Choosing the right lumber for a deck comes down to one question: what’s the code-compliant, long-lasting material for the job? For most US projects, that answer is pressure-treated wood for structural parts, with options for the surface boards. The wrong choice — like using above-ground rated lumber in ground contact — can fail inspections or rot within a few years.
Framing Lumber: Why Pressure-Treated Wood Leads
For joists, beams, posts, and stair stringers, preservative-treated lumber is the default and usually the only code-compliant option. These structural members carry the deck’s weight and sit close to moisture, so they need chemical protection against decay and insects.
Southern Yellow Pine dominates the US market for treated framing lumber. It accepts preservatives deeply and delivers high strength, which is why lumberyards stock it for most residential deck builds.
Deck Boards: Treated vs. Naturally Durable Species
For the surface you walk on, you have two main categories: pressure-treated decking or naturally durable woods. Treated decking, often in 5/4 in. x 6 in. or 2 in. x 6 in. boards, resists rot and comes at a reasonable price. Cedar and redwood offer a more attractive appearance but carry strict requirements.
Most standard-grade cedar and redwood you buy at a home center fails this test. That’s why naturally durable wood is not automatically code-compliant just because it’s a “premium” species.
Use Categories and the Label That Matters
Not all treated lumber is the same. The AWPA describes use categories that tell you where each product belongs: UC3B covers above-ground, weather-exposed parts like deck boards and railing, while UC4A through UC4C apply to components with increasing ground contact.
Check this label before installation — it’s the fastest compatibility check you can perform.
| Component | Lumber Required | Key Requirement |
|---|---|---|
| Joists, beams, posts | Pressure-treated framing lumber | UC4A ground-contact for posts |
| Stair stringers | Pressure-treated framing lumber | UC3B or higher |
| Deck boards | Pressure-treated decking or durable species | UC3B above-ground rating |
| Naturally durable wood | Cedar, redwood, locust, walnut | Max 10% sapwood per face |
Field Cuts and Fasteners Matter
Cutting treated lumber exposes untreated interior wood. Skipping this step invites rot at exactly the places where water collects.
Higher-retention treated wood also demands corrosion-resistant hardware.
What About Artificial Lumber Decks?
If you’d rather skip the maintenance entirely, our roundup of the best artificial lumber deck options compares the leading composite and PVC boards side by side.
That said, composite works best for deck boards. Framing members beneath it are usually still pressure-treated wood, since composites lack structural strength for joists and beams.
What Kind of Lumber for Deck? The Bottom Line
The shortest safe answer: specify pressure-treated lumber for all framing members, choose above-ground treated decking or a verified naturally durable wood for the surface, and confirm every board’s stamp before you buy. Local building departments control the final call, and some jurisdictions impose retention levels stricter than the national baseline, so confirm your selections with an inspector before ordering materials.
References & Sources
- American Wood Council. “Prescriptive Residential Wood Deck Construction Guide.” Covers framing requirements, field treatment, and fastener specifications.
- Southern Pine Association. “Pressure-Treated Southern Pine.” Details use categories, retention levels, and common board formats.
- Government of British Columbia. “Preservative Treatment Standards.” Explains sapwood limits and treatment quality marks.