This Architectural Drawing is AutoCAD 2d drawing of Lateral Flashing in Rainwater Gutters Details. Gutter flashing is a long piece of aluminum or plastic material that fits between your gutter and your roof line. The purpose of flashing is to prevent water from going behind your gutter. Some types of roof flashing are counter flashing, chimney flashing, step flashing, headwall flashing (also called apron flashing), valley flashing, and gutter apron flashing. For more details and information download the drawing file.