We have a garage attached to our house, but no doorway into it. We want to put a patio door in but discovered that the garage floor is 20 inches below the housefloor. In the garage, the height from the concrete floor to the rafters is only 100 inches, thus there would only be 80 inches left for a door, and this is the smallest rough opening for standard doors that I've been able to find. Marvin windows can make me a custom door of 6 foot 1 that would leave me about 4 inches for a header. Would a 4-inch I-beam be enough to support the load above a five-foot wide opening? Yes, I realize that people will be bumping their heads but the house has such an odd design, it's all we can manage right now.