I have a light basement with 3'6" foundation walls with windows framed above. The finished height of the window sill is 5" above the concrete sill. I want to frame a knee wall in front of the foundation wall with a reclaimed wood ledge shelf capping the knee wall and foundation wall. I have 1/2" of spray foam on the concrete walls and sill and want the windows trimmed with 3.5" trim. If I cap/attache the framed knee wall to the sill plate framing with 2X lumber I will not have enough space for the full trim. Can I use galvanized corner brackets to attached the top of the framed knee wall to the concrete foundation wall and then just cap with the 3/4" reclaimed wood or does code require that I use structural lumber to cap/join the framed knee wall to the foundation wall? If I use metal brackets to secure the framed wall, how to I anchor the reclaimed wood to the sill plate framing?
I believe you will want to attach 1.5" thick material to the sill plate and have that come out to the top of your knee wall. If you do not do this you will have a dickens of a time trying to adequately attach the reclaimed lumber in a secure manner to prevent it from cupping and warping over time.
With regard to the windows...why not just use a separate flat window stool at the bottom of the window and use your desired window trim on the left, right and top of the window. There is nothing to say that the apron trim under the sill board has to be a matching trim to the casing around the window. Below is a picture of one such application.