Flashing a shallow recess. At the bottom of the window, first caulk the framing, then apply pre-fit corners to the outside edge of the recessed opening.
Make two slits at the edge of the opening, and fold the inner tongue of the flashing across the horizontal sill and up the inner face below the window opening, rolling it smooth with a J-roller.
Cut short pieces of flashing membrane to create end dams on both sides of the recessed opening. Here, the end dam pieces are bedded in caulk before the installer rolls the edges.
Black paper is installed as a protective layer over the horizontal surface of the recess, and a final membrane “apron” to tie in with the WRB is installed on the face of the framing.
With the side flashings in place, the window unit can be installed. (To meet the window manufacturer’s requirements, the window flange must be installed in a bed of sealant; see “Installing Flanged Windows,” Jan/16.)
Remember that the top corners, not just the bottom of the recessed opening, must also be flashed. Install flashing corners on the inner face near the top of the window first ...
The final membrane flashing is slit at the edges of the opening and folded inwards across the horizontal head and down over the window flange.