I just finished installing 4 picture windows, 2 are separated by a 2x4 between them. The house is brick.
These windows have a integral J channel all around. It is about 5/8 wide about 1" forward of the nailing strip. I would like to fill the air space behind it. The easiest way would be to remove it. It has a groove at the window casement, It looks like it would break off pretty easy. Is it an option to remove it or do I have to fill it with foam or fiberglass?