Flashing (weatherproofing) Information
Flashing (weatherproofing) is a product used to provide a weatherproof seal around penetrations in a building's roof or walls. It consists of a thin layer of waterproof material that keeps water from getting into places it does not belong. It is used around roof penetrations such as the edges of skylights, chimneys, vent stacks and vent fans as well as at intersections of roofing surfaces such as roof valleys. It is also used around penetrations in vertical surfaces such as around window and door sills. As water lands on a building's exterior, flashing directs it over and past crevices, cracks and gaps so that it does not come in contact with vulnerable building materials.
Flashing must be installed so no seams face upward. It is usually layered with other building materials to provide a clear flow of water past any openings in the building. For instance, the upper edge of flashing is protected by house wrap or tarpaper, not installed over it.
Below are some common types of flashing. Most are defined by the application in which they will be used. There are many different shapes and configurations of flashing available to accommodate its various uses. Care should be taken to choose the right flashing for the job.
- Chimney flashing is applied around the base of a chimney in several parts.
- Continuous flashing protects the joint between a vertical wall and a sloped roof.
- Drip edges prevent water from seeping under roofing along the edges of rakes and eaves.
- Step flashing steps up a roof to protect where the roof meets the side walls of dormers.
- Valley flashing protects the valleys where two roof planes meet.
- Vent pipe flashing fits over flues and pipes. It is cone-shaped with a flange at the base.
- Window flashing - This is the basic thin sheet of metal that can be easily bent and molded to fit a space.
- Tape—Newest form of flashing and comes as a self-adhering flexible membrane.
Many materials can be used for flashing. As long as it won't degrade from contact with incompatible materials it should work. Flashing is typically produced as a sheet of aluminum, copper, PVC, steel, or lead, but may also take the form of a flexible rubberized sheet.
- Aluminum—Easy to form, durable and relatively inexpensive
- Bituminous Ffashing tape—Tar like material with a sticky backing
- Copper and lead-coated copper—Harder to form than aluminum but very durable
- Lead—Very soft and easy to bend. Very durable
- Galvanized steel—Inexpensive but not as durable as others
- PVC—Easy to work with and inert