Flashing a wood-framed chimney is like flashing a dormer, except there’s no roof behind it. Without protection, water can leak into the joint and rot your walls to direct uphill water away
An item on the Energy Star Thermal Bypass Checklist. Item 5.1.2, to be exact ...
Just because you draw it doesn't mean they'll build it that way. Know what makes sense, what the framer can execute, and forget about designing in two-foot modules