Pressure-Treated Lumber
Pressure-treated lumber is dimensional softwood (typically Southern Yellow Pine) infused with preservative chemicals under pressure to resist rot, decay, and insect damage. The most common decking and structural lumber for outdoor applications.
Fast Facts
- What Is It?
- Southern Yellow Pine or Douglas Fir impregnated with preservative (ACQ, MCA, or CA-C) to resist rot and insects.
- Common Uses
- Deck framing, deck boards, fence posts, retaining walls, landscaping structures, ground-contact applications.
- Cost Range
- $0.80–$2.50 per linear foot for 2×6 depending on treatment level and market conditions.
- Durability
- Above-grade: 15–30 years. Ground-contact rated: 30–50+ years with proper maintenance.
Specifications
| Property | Value |
|---|---|
| Standard | AWPA U1 (Use Categories UC3A–UC4C) |
| Common Preservatives | ACQ (alkaline copper quat), MCA (micronized copper azole), CA-C |
| Ground Contact Rating | UC4A/UC4B — 0.15–0.40 pcf retention |
| Above-Grade Rating | UC3B — 0.10 pcf retention minimum |
| Fastener Requirement | Hot-dipped galvanized, stainless steel, or manufacturer-approved coated fasteners |
| Typical Species | Southern Yellow Pine (SYP), Douglas Fir-Larch, Hem-Fir |
What Is Pressure-Treated Lumber?
Pressure-treated (PT) lumber is softwood dimensional lumber that has had chemical preservatives forced deep into the wood fibers through a vacuum-pressure process. This treatment dramatically extends service life in wet, humid, or ground-contact environments where untreated wood would rot within a few years.
Treatment Chemistry
Modern PT lumber uses copper-based systems: Alkaline Copper Quaternary (ACQ) and Micronized Copper Azole (MCA) are the two most common in residential construction. These replaced chromated copper arsenate (CCA), which was phased out for residential use in 2003. Copper provides fungal and insect resistance; the quaternary or azole compounds enhance performance against copper-tolerant organisms.
Choosing the Right Use Category
The AWPA Use Category system rates PT lumber for specific exposure conditions. UC3B covers above-ground applications (deck boards, railings, horizontal framing). UC4A covers general ground contact. UC4B covers severe ground contact (permanent structures, high moisture). UC4C is for saltwater splash zones. Always specify the correct use category for your application.
Handling and Safety
Wear gloves and eye protection when cutting PT lumber. Never burn PT lumber — the smoke contains concentrated preservative chemicals. Wash hands before eating after handling. For residential decks, modern ACQ and MCA preservatives are considered safe for incidental skin contact when dry.
Frequently Asked Questions
Can I use any fasteners with pressure-treated lumber?
No. Modern ACQ and copper-based preservatives are highly corrosive to standard zinc-plated fasteners. Use only hot-dipped galvanized (HDG) ASTM A153, stainless steel (304 or 316), or manufacturer-approved coated fasteners. Check the preservative's manufacturer data sheet for approved fastener specifications.
What is the difference between UC3B and UC4A?
Use Category UC3B is for above-ground applications protected from direct water contact, like deck boards and railings. UC4A is for ground contact (posts, sill plates) and requires higher preservative retention. Match the use category to the application — using UC3B lumber in ground contact will void warranties and shorten service life.
How long should I wait before painting or staining pressure-treated lumber?
Wait until the lumber has fully dried (MC ≤ 19%). Kiln-dried after treatment (KDAT) lumber can be stained immediately. Wet-treated (green) lumber may need 3–6 months outdoors before applying a finish. Test with water — if it beads, wait longer.
Related Guides
Comparisons Featuring This Material
Cedar Decking vs. Pressure-Treated Lumber
Cedar and pressure-treated lumber are the two most popular natural wood deck board options. Compare appearance, durability, cost, and maintenance so you can choose the right deck board for your project.
Composite Decking vs. Pressure-Treated Lumber
Composite vs. pressure-treated lumber is the central decking decision for most homeowners. Compare upfront cost, total ownership cost, maintenance burden, lifespan, and performance to make the right choice for your project.
Also Consider
Cedar Decking
Western Red Cedar (Thuja plicata) is a premium natural decking choice valued for its natural decay resistance, dimensional stability, and warm appearance. The go-to natural wood deck board for contractors and homeowners seeking a traditional aesthetic.
Composite Decking
Composite decking combines wood fiber and recycled plastic (PVC or polyethylene) into a board that mimics the look of natural wood with dramatically lower maintenance requirements. The fastest-growing segment of the decking market, with top brands including Trex, TimberTech, and Fiberon.