Many references recommend placing end dams at flashing terminations over window lintels. Are these end dams necessary? If water flows off the end of the flashing, won't it merely be handled by lower levels of flashing?

If you do not provide end dams on flashings, water flowing off the end of the lintels can cause deterioration and leakage problems. Water can cling to the underside of the flashing and may flow onto the surface of the lintel, accelerating the corrosion of these lintels. In addition to accelerating corrosion, water on the lintels can flow around the end of the angle and cling to the underside, causing water leakage at the window jambs. Water flowing off the end of the lintel can also saturate the masonry at the jambs, which can contribute to efflorescence problems or accelerate freeze-thaw degradation in cold climates.

Placing end dams on flashings will avoid these problems by ensuring that water cannot flow off the end of the lintels. It is important to extend the edge of the flashing and end dam to the face of the masonry and install sealant between the underside of the flashing and the masonry below at the jambs. This will stop water from re-entering the wall at the ends of the flashing. Placing a weep hole at the end dam will further assist in draining water at this location.