Are cedar shingles and copper flashing compatible?
Shingles, if installed in direct contact with metal flashing, will wick water through capillary action under the leading shingle edge. The water will tend to remain in contact with the flashing and build up in acidity. This acid-laden water will corrode flashing in a linear fashion leading to “line corrosion” or pinholes in the flashing. The correct detail is to raise the leading shingle edge on a cant thus breaking the bond between shingle and flashing. Extensive details are included in CDA’s Copper in Architecture Design Handbook.
