I built my house 10 years ago and one of the mistakes I made was installing a 16 foot by 7 foot garage door. Now I want to raise the door 21 inches by adding another panel to my rollup door. The big job is raising the header 21 inches. My garage is 23 feet wide and when we installed the header we ran the header all the way across the width of the garage so the header is 23 feet long. It is going to be difficult to raise the entire 23 feet so I was thinking about cutting the header so that it would be 16 foot and 6 inches. (The header would be above the door only not spanning the entire width of the garage) I would have two trimmers under each end of the header and a 4" X 4" stud at the ends of the header going floor to ceiling. My ceiling height is 10 foot 3 inches. Do you see any problem with my plans?