Flashing systems should prevent water that permeates masonry from entering the interior. However, sometimes flashing systems fail, usually due to small overlooked details. DISCONTINUOUS FLASHING Water will eventually leak through any gaps in the flashing. Some typical discontinuity problems are: flashing stopped at corners; flashing terminated at vertical expansion joints; no end dams where masonry meets other wall systems; and improperly sealed flashing laps. FLASHING THAT DOESN'T PROJECT FROM THE WALL FACE Sometimes to conceal the edge of the flashing, architects specify that the flashing be held back from the face of the wall. This detail usually does not work well. To install flashing properly, extend the flashing beyond the face of the masonry and form a drip. TOP EDGE OF FLASHING NOT COVERED If the top edge of the flashing is not sealed or covered, water running down the face of the backup will get behind the flashing. Sometimes water can get behind flashings in veneer construction even if the building paper laps over it. This is usually because water gets behind the paper. To prevent this, lap building paper at least 4 inches both vertically and horizontally.