The easiest way to make something leak is to punch holes in it. Building walls are no exception. And although no one wants a leak, we have to punch holes in them for windows, doors, and other things. Opening tolerances, lateral placement, head, and sill details all affect the relative success or failure of moisture control at these holes in the wall. HEAD DETAILS Precast concrete, stone, loose steel angles, and reinforced masonry lintels are all used to span window openings. Any structural member that supports masonry must be limited to a deflection of 1/600 to prevent cracking in the masonry above. Any supporting member anchored directly to the structural frame must be flexibly attached to the window frame to allow for differential movement and frame shortening. Install flashing above the window to collect moisture that has penetrated from above and re-direct it to the outside. Where the flashing stops at each side of the window, turn it up to form end dams. This keeps water from running off the ends and down into the wall. SILL DETAILS Two potential sources of moisture must be dealt with at window sills. The first is water that penetrates the masonry sill; the second is water that enters the window system through gaskets or sealant joints at the outside glass light. The more mortar joints in a masonry sill, the more opportunities there are for water to enter the wall, and the more critical sill flashing becomes. WEEP HOLES Anywhere flashing collects moisture in a masonry wall system, weep holes are needed to allow that moisture to escape. Open head joints, cotton wicks, and plastic tubes are used most frequently at lintel flashing, although plastic tubes clog too easily to be reliable.