Is flashing needed above windows in grouted or mortared barrier walls?
In general, installing flashings above the head of windows in barrier walls is recommended. They are not, however, as critical as they are in cavity walls. In a cavity wall, water readily flows through the open cavity space and reaches the flashings. For this reason, the flashing must be made watertight and contain appropriate end dams in order to direct the water to the exterior. In grouted or mortared barrier walls where the collar joint is filled, water does not move freely through the wall system. In these cases, the masonry materials absorb much of the water. Flashings are often provided in barrier walls to protect the steel lintel from water that will cause corrosion and to provide additional protection from water penetration to the interior at the level of the lintel. As with cavity walls, flashings at lintels in barrier walls should project beyond the face of the wall and have end dams. Many older buildings with solid masonry walls, recessed windows and lintels do not have flashings. Such buildings may not experience any significant leakage until the masonry weathers or until the masonry cracks, displaces or deteriorates as a result of lintel corrosion. Excessive moisture will accelerate corrosion. Expansive pressures generated from corroding steel lintels will cause further cracking and distress. Flashings will protect the lintel from direct contact with moisture. This will reduce the rate of corrosion and control any leakage.