Use corrosion-resistant nails and joist hangers unfortunately, boosting the copper content in lumber not only makes the new pressure-treated wood more expensive than the old, but it also makes the new stuff significantly more corrosive -- 5 times more to common steel, according to American Wood Preservers Association (AWPA) test results.

Due to the high risk of galvanic reaction between the copper-impregnated wood and any dissimilar metals, fasteners and flashings should be stainless steel and copper whenever possible. Electrogalvanized stock is rated with a class scale that ranges from 5 to 110. Hot-dipped galvanization ratings are based on the actual weight of the coating. For example, a G-60 rating means that there's 0.60 oz. of zinc per sq. ft. of metal.

The G-60 and G-90 hot-dipped coatings are what we've been using until now. But engineers suggest stepping up to the heavier G-185 coatings for hot-dipped galvanized products, and they recommend class ratings of 40 or above when using electrogalvanized fasteners, such as expansion bolts.

Currently, G-185 is the best galvanized protection that you can buy. As for nails and screws, many of the composite coatings that are currently available are still good for the new treatments (see www.osmose.com to read about fastener recommendations), but you should verify this by carefully reading the label.

Perhaps the most important point to keep in mind relating to copper-based wood treatments and galvanic corrosion is to avoid aluminum flashings altogether. Aluminum corrodes quickly in the presence of high copper concentrations.

From http://www.taunton.com/finehomebuild...ges/h00127.asp