- Q. Is ACQ-treated lumber and plywood suitable for building permanent wood foundations?
A.Merritt Kline, a product support specialist with APA/The Engineered Wood Association and the Southern Forest Products Association, and Bob Clark, an engineered wood specialist with APA, respond: According to the American Wood Preservers' Association (www.awpa.com), recommended preservatives for plywood and southern pine lumber intended for use in the construction of permanent wood foundations (PWFs) include .60 alkaline copper quat — types C and D (ACQ-C and ACQ-D) — and .31 copper azole — type B (CA-B) — in addition to .60 chromated copper arsenate (CCA).
Unfortunately, the Southern Pine Council's Permanent Wood Foundation Design & Construction Guide (which can be downloaded at newstore.southernpine.com/cgi-bin/newsopine/product?;32) does not address this new generation of waterborne treatments. However, there's no reason to believe that fundamental design and detail recommendations would be different for ACQ- or CA-B-treated wood, other than the need for additional corrosion protection; that requirement can be satisfied by using hot-dip-galvanized fasteners that meet ASTM A153 specifications and connectors that meet ASTM A653 Class G185 specifications.
Although the Southern Pine Council and APA/The Engineered Wood Association no longer provide technical support for PWFs, the American Wood Council (www.awc.org) is in the final stages of reviewing a new PWF design guide. Our understanding is that the guide was developed through a consensus process, which will make it eligible for adoption as a building code reference standard.
By the way, in case you wondered, even though the EPA has prohibited the use of CCA for most residential applications — such as play structures and decks — since January 2004, the agency continues to authorize .60 CCA-treated softwood lumber and plywood in residential and light-commercial wood foundations.