Parapet walls require a metal cap flashing to prevent water from penetrating from the top of the wall. Since a cap flashing sheds water, it must be sloped toward the roof to prevent staining of the exterior cladding. In addition, it cannot be made waterproof at the joints, and requires a secondary, continuous and waterproof flashing below it.
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Note : Parapet walls are an extension of the wall at the roof edges to form a terrace or walkway.