Masonry Magazine May 1978 Page. 14
FLASHING PLACEMENT
Design Considerations. Exposure to rain is a basic consideration in design against moisture penetration. It varies greatly throughout the United States; e.g., severe along the Gulf Coast, the Atlantic Seaboard, and the Great Lakes; moderate through the Midwest; and slight in the far Southwest. Recommendations in this Technical Notes apply to severe or moderate exposures. Where exposure is slight, internal flashing at spandrels, lintels, sills, etc. may be eliminated and external flashing may be reduced to a minimum.
Where flashing extends to the interior, place its end between furring and the interior finish and turn it up at least 1 in. to collect moisture that may penetrate through the wall.
Wall Base.
Any moisture which does enter a wall gradually travels downward. Place flashing above grade at the wall base to divert this water to the exterior. To stop the upward capillary travel of ground moisture, especially where there are no basements, place damp checks about 6 in. above grade. In areas where first floor wood joists require protection from termites, use a metal damp check which projects at least 2 in. past the inside face of the wall, and which is bent down at an angle. (See Fig. 1.)
overhanging projections. At steel lintels, place flashing under and behind the facing material and over the top of the lintel and bend its outer edge down to form a drip. (See Fig. 3.)
Window Sills.
Place through flashing under and behind all sills except, perhaps, impervious monolithic sills. Extend ends of sill flashing beyond the jamb line on both sides and turn them up at least 1 in. into the wall. Slope all sills to drain water away from the building. Where the undersides of sills do not slope away from the building, provide a drip notch or extend flashing and bend down to form a drip. If water which runs down windows and over sills continues down the building face, it is likely to create stains. (See Fig. 2.)
Opening Heads.
Install through flashing over all openings except those completely protected by
Spandrels.
In skeleton-frame structures, spandrels may be flashed continuously at beams, or with reglet. When the entire spandrel is flashed, two-piece flashings may be used, provided they are lapped at least 4 in. When cavity walls are supported by concrete spandrel beams, place the flashing on the shelf angle and extend it at least 8 in. up the beam and anchor it into a reglet. When galvanized or stainless steel covered angles are used, flashing may not be necessary except to cover joints between lengths. (See Fig. 4.)
Projections and Recesses.
Projections and recesses tend to hold rain water and snow. They should have a top slope for drainage and, if possible, a drip to keep the water away from the wall surface below. Place flashing over the top of pro-