What is pressure treated lumber?

Pressure treated lumber starts as standard wood (typically southern pine, Douglas fir, or hem-fir) that is placed in a sealed chamber and forced into chemical preservatives under high pressure. This process drives the preservative deep into the wood fibers, creating a barrier against rot, termites, and decay that would otherwise compromise a deck's structural integrity.

The treatment level depends on where the wood will be used. Ground contact rated lumber contains higher preservative concentrations because it will directly touch soil or be buried, making it suitable for deck posts and supports that sit on concrete or earth. Above ground rated lumber has lighter treatment and works for joists, rim boards, and fascia boards that remain exposed to weather but do not contact the ground. Both types prevent the breakdown that moisture and insects cause in untreated wood.

Southern pine dominates pressure treated stock in the Greater Charlotte region due to availability and cost. The chemical treatment typically uses copper-based preservatives that are odorless once dry and safe for residential use. Treated lumber still requires proper fastening with stainless steel or hot-dipped galvanized hardware to prevent corrosion where metal meets treated wood. Most deck builders in the area stock pressure treated lumber as the baseline structural material, though homeowners may choose alternatives like cedar, composite, or tropical hardwoods for visible surfaces. A qualified deck builder will specify the correct rating for each component and ensure proper ventilation and drainage to extend the deck's life.