Tech Today

Fastener corrosion and treated wood

In February 2005, NRCA issued a Special Report titled "Use of treated wood in roof assemblies," notifying its members of changes in the chemical treatment of preservative-treated wood and the resulting concerns with fastener corrosion associated with the new chemical treatments. Because NRCA's concerns with possible corrosion continue, following is current information and NRCA's latest recommendations.

Background

As of January 2004, wood preservers voluntarily removed wood treated with chromated copper arsenate (CCA) from consumer markets, citing concerns the arsenic and chromium contained in CCA pose possible environmental concerns in exposed-to-weather applications. CCA treatment had been used successfully for preservative-treated wood since the early 1930s, and those in the roofing industry had grown accustomed to specifying and using CCA-treated lumber as wood blocking and wood nailers in roof assemblies.

Wood preservers have introduced a number of preservative treatment substitutes, including alkaline copper quant type C (ACQ-C), alkaline copper quant type D carbonate (ACQ-D carbonate), micronized copper quant (MCQ), copper azole (CBA-A, CA-B), ammoniacal copper zinc arsenate (ACZA), sodium borate disodium octaborate tetrahydrate (SBX/DOT) and zinc borate.

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