I'm installing a wood window in a basement where the wood frame
cripple walls are about 3.5' tall. To maximize window height I cut
out a 1' tall section of the foundation, and the window will sit in
the cutout on a PT 2x6 sill plate. What is the proper flashing detail
for the bottom of this opening?
Further details: The sides of the opening also have 2x6 PT trimmer
studs. Because of overpour the exterior face of the foundation at the
bottom of the cutout projects about 1.75" past the outer edge of the
PT sill. I have made a redwood window sill which will sit on the PT
sill with a 1/2" rabbet and project 2.75" past the outer edge of the
sill. This leaves a 1" gap between the underside of the redwood
window sill and the top of the concrete. The window itself is just a
box which sits on the redwood window sill, there is no nailing flange.
A scale ASCII art cross-section is below.
S = redwood window sill, cut from 2x4
M = 2x6 PT sill
B = 2x6 PT side buck or trimmer stud
C = concrete
Scale: XX = 1/2" square
B B 12" up to adjoining mudsill
C 8" down to grade