Window Flashing (as seen here) is a thin continuous piece of material that is installed to prevent water from getting into a structure from an angle or joint near windows. It is key in preventing water intrusion. Window flashing is arranged in a manner that directs water down and away from the structure. It is typically used on roofs, around windows and doors, and around any opening for pipes or electrical lines.
The flashing typically used around windows and doors is concealed within a construction assembly, can be sheet metal (as aluminum flashing around in corners), or a water proofing membrane such as bituminous fabric or plastic sheet material.
Flashing can be used in a number of ways. Wall flashing is embedded in a wall to either direct water that has penetrated the wall back outside or installed to prevent the entry of water into the wall. Wall flashing is typically found around windows and doors. Sill window flashing is a concealed flashing that is installed under window sills or door thresholds to prevent water from entering a wall at those points. Base flashing is found at the base of a wall and usually has weep holes to let water escape. It is installed at the building grade.
Window flashing is important because it is the only way to prevent water intrusion. Improperly flashed roofs, windows, doors, and other openings will leak and cause dry rot. A good seal guides water around the opening and keeps the interior wall protected and dry. Properly installed, window flashing will control almost all water intrusion into the structure and will work for the life of the structure.
Flashing for wall penetractions
This picture is showing a flashing product used to seal around an outside vent. This type of flashing stops air leakage and helps to prevent water intrusion. It eliminates the need for sealants and is easy to integrate with building envelope and works with all cladding systems. This also helps to reduce bug and vermin infestation.
House Wrap is shown here by sealing the building envelope, with a High quality building paper or "wrap." It helps to reduce nasty drafts and control air leakage, which helps to maintain the installed R-values of insulation. This helps heating and air conditioning systems to run more efficiently, saving energy and lowering your utility bills, while keeping you more comfortable year round. Sealing the building envelope also helps protect your home against bulk water intrusion and air-transported moisture. These two factors can dramatically reduce the effectiveness of your insulation and also lead to mold and mildew, and even wood damage as the water accumulates in your wall system.