Wood Deck Failures

What happened to pressure treated deck lumber?

Pressure treatment is a process that forces chemical preservatives into the wood. The wood is placed in a closed cylinder and pressure is applied to force the preservative into the wood. Preservatives protect wood from decay and insect damage. There are 3 classes of wood preservatives; the waterborne method is typically used in residential construction. For decades the lumber industry successfully used CCA, chromated copper arsenate, as the preservative of choice. However negative publicity regarding the arsenate caused the wood product industry to voluntarily transition away from CCA to alternative preservative systems. CCA has no longer been used residentially since December 2003. A number of alternative preservatives are available. The most recognized are ACQ, alkaline copper quad, and CA, copper azole.

Testing has indicated that ACQ and CA are more corrosive to steel and the protective coatings applied over steel.

In other words, the old galvanized nails, screws, metal hangers and connectors were no longer approved for use with the ‘new’ pressure treated wood. Unfortunately, either nobody told the builders and lumber suppliers or they just didn’t care. Hot-dip galvanized or stainless steel fasteners and hardware are the recommended products to use. The structural stability of the wood deck depends upon using these approved fasteners.

When you see rusted nails, bolts, and other metal hardware on a wood deck, it is a big problem.


Doug Hastings
MN Home Inspector, Minneapolis & St. Paul
ASHI certified inspector, ACI
Kaplan University, Home Inspection Lead Instructor

‘Pops’ Rob Leslie
Kaplan Professionals, Retired


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