Homeowner with some construction experience. We have a ranch house with a walk out basement. In our bedroom, we have a wall that partially bumps out with a 96 x 72 window (3 gang double hung). There is a knee wall with a ledge/seat. The window is drafty, but the whole wall is cold, about 20-25 degrees colder than the rest of the bedroom when temperatures drop to single digits or zero. I took the ledge off last fall and made sure it was well insulated and sealed the edges and corners with spray foam. That did not help. We ended up putting putty around the window, the seam between the seat and wall, and baseboards and floor. We put the plastic film over the entire opening and down to the floor. This helped some, but it was still cold.

I am considering having the bumped out wall removed, and replacing the window with a new construction window so everything can be flashed, sealed, and weatherproofed as much as possible. The window would no longer be recessed and the bump out would be gone, eliminating the extra sides and corners where cold air could infiltrate.

I would like to understand what those steps should look like to educate myself. Since the bump out does not go to the ground and the roofline does not hang out, I am pretty certain there are no structural issues. I have attached a couple pictures for reference. Thanks for any insight. We live in central Indiana.