Just before installing a sliding glass patio door today in our self-built home, we measured the rough opening and it is 1-3/4 inch too short for the height of the slider. (The slider is 6 feet wide by 6 feet 6 inches tall.) How this happened is anyone's guess. At any rate, we have two choices (I think):
A. We completely remove the header and the cripples above it, reduce the height of the cripples by 1-3/4 inch, and use shims and a 2x6 piece cut to fit in under the left and right sides of the header on the jack studs to increase the height of the rough opening by the necessary amount.
B. We use a Sawzall to cut off the bottom 1-3/4 inch of the header across its length.
Problems we see with both fixes:
A. This is a load-bearing roof-end wall. Even if we work fast, there is the potential for sagging once the security and strength of that header is completely removed from the framing. Can we possibly hold it up with temporary framing while we do what we need to do before replacing the header in its new position? Use a wall jack? (We don't have a wall jack.)
B. We used three 2x10s with 1/2 inch plywood sandwiched between to create the header. Taking 1-3/4 inch away from the header will, in essence, create a 7-1/2 inch header. Is that strong enough over the six foot width of the door to sufficiently support the roof?
There could absolutely be another fix we're not seeing...we're not builders by trade.