Can Pressure-Treated Lumber Rot?
Many homeowners assume that because their deck is built with pressure-treated lumber, it cannot rot. This is a dangerous misconception. Pressure-treated lumber is rot-resistant, not rot-proof. The chemical treatment penetrates the outer layer of the wood, but cut ends, drilled holes, and joints expose untreated interior wood. At these points — and anywhere moisture is consistently present — decay fungi can establish and spread.
Key Takeaways
- Pressure-treated lumber is rot-resistant, not rot-proof
- Cut ends, drilled holes, and notches expose untreated interior wood
- Connections where two members meet trap moisture and are prime rot locations
- Ground contact — even with treated posts — accelerates decay at the post base
- Field treatment of cut ends is required by code but frequently skipped by contractors
- Older CCA-treated lumber (pre-2004) is more corrosive to fasteners, accelerating failure
- A probe test during NADRA inspection identifies internal rot not visible on the surface
About the Author
Independent flooring inspector serving Southern California. Certified as NWFA Certified Inspector (#CP2416122), FCITS Master Inspector (#2031), NALFA Inspector, IFCII Inspector, and CFI University graduate. Specializes in forensic flooring investigations, moisture diagnostics, insurance claims, and expert witness services.
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