Metal Base Flashing and Bituminous Counter Flashing Problems

The use of metal base flashings in the construction of built-up roofs is not recommended. Metal base flashings easily separate from bituminous materials and stripping felts crack at the edge of the metal because of the difference in expansion coefficients between the materials. Open joints between metal pieces and deterioration of the metal are also sources for water entry. Inside and outside corners are particularly vulnerable areas. For these reasons, metal base flashings should be replaced with bituminous base flashings whenever possible.