We're getting the roof installed on our house and have copper valley, step, and drip edge flashing installed under asphalt shingle. I noticed the other day that the roofers are using galvanized steel nails to hold down the copper. From everything I know, dissimilar metals in the presence of an electrolyte (water) will electrolytically corrode the less noble metal, in this case, the nails. My roofer is saying that this won't be an issue since all the nail heads aren't going to be exposed to water (under the shingle, siding, or underlayment). I guess I have a few questions: Is he right or wrong, and how much moisture would cause electrolytic corrosion? Is he just cutting corners and saving money? Should I insist they re-do it? About 80% of the roof is installed.