Flashing a deep window recess. Start by applying the sill apron across the outside face of the wall, and caulk the corner of the recess.
Strips of flashing are first folded along both sides of the recessed opening, then slit so the outside edges can fold onto the exterior face of the wall.
Next, the inner flashing corners are installed with caulk under them. At the front edge of the recess, the author installs a “bridge flashing” spanning between the two flashing strips at the corners.
The end dam is installed next, spanning the distance from the window opening to the outside face of the wall.
The author always installs a protective layer of black paper to ward off damage to the bottom of the recess during construction. A final sill membrane flashing is applied over the black paper below the window opening.
After side flashings are in place, the window unit is installed and flashing corners are installed above the window.
Next, the top corners of the recess are flashed, and a head flashing is installed over the window flange.