Counter-flashing is a technique used in order to help prevent moisture from penetrating a home behind the vertical flange of a headwall or sidewall flashing. Thin pieces of material are installed in order to prevent water from passing through a structure at its joint. This weather resistant barrier (WRB) system is imperative in new home construction. Sometimes this exterior wall covering will serve as counterflashing itself and sometimes a separate element is installed. This is especially important in structure where walls are either brick or stone.
Counterflashing in brick walls is more expensive to do especially in those with poorly installed structures that simply rely on a sealant alone. The sealant will eventually dry, shrink and crack, allowing moisture to invade the home. Flashing materials can be either concealed or exposed; however they both do the job. Exposing flashing materials typically consist of copper, lead, aluminum, stainless steel or other architectural metals.
Flexible flashing materials that are typically used around window and door openings include acrylic, rubberized asphalt or butyl rubber. This types allow for easier installation and are great for homes that are older that need added protection, but should not be used as the only moisture prevention technique in a home (especially during new construction). Counterflashing is typically used in walls, under windows or doors or on roofs in order to waterproof cables, supports and other roof components.