Asphalt, wood shakes, slate and other overlapped roofings are fine until they meet an obstruction. Up against a dormer, a vent pipe, a chimney, they need flashing — a patchwork of metal sheets, and ...

Flashing is a good way of preventing water from entering a dwelling at the point where the roof meets the walls. To begin the installation, fold a five-by-seven piece of aluminum flashing lengthwise.