Flashing (weatherproofing)

Flashing is thin pieces of impervious material installed to prevent the passage of water into a structure from a joint or as part of a weather resistant barrier system.

Before the availability of sheet products for flashing, builders used creative methods to minimize water penetration.

The introduction of manufactured flashing decreased water penetration at obstacles such as chimneys, vent pipes, walls which abut roofs, window and door openings, etc., thus making buildings more durable and reducing indoor mold problems.

[citation needed] Moreover, flashing is important to ensure the integrity of a roof prior to a solar panel installation.

[citation needed] Builders' books, such as Loudons An Encyclopædia of Cottage, Farm, and Villa Architecture and Furniture... gave instructions on installing lead flashing by 1832 and in 1875 Notes on Building Construction provided detailed instruction and is well illustrated with methods still used today.

An important type of potential chemical reaction between metal flashing materials is galvanic corrosion.

Copper and lead cannot be used in contact with or even above aluminium, zinc, or coated steel without an increased risk of premature corrosion.

In the US and UK, at least, lead flashing and fittings are still readily available, despite the environmental concerns associated with bulk use of this heavy metal.