This is how I had built a loft, over the rear-half of a 2-car garage. It's about 240 sq. ft. The Simpson galvanized brackets on the rear CBS wall (pic.#1), fastened to PT 2" X 8", tie-into the 4" X 8" X 1/2" thick steel box beam's brackets at the middle of the garage. That box beam is welded into steel plates in the poured-column/CBS side walls, (pic. #2) halfway from the front to the back. In pic. #2, the 4" X 8" steel box beam is not yet welded to the steel plates in the garage side-walls, about 7' up from grade. The inlaid steel plates are ~8" X 12".
You can also see the gable end wall has a steel ridge beam w/thick welded plates for the rafters-no trusses. The entire gable end wall where the double single-car OH doors are, is all poured concrete, from the footers to the header beams for the side walls. The end gable wall w/the OH doors has lots of steel, much of it nearly 1" dia.
If we ever have a hurricane, this is going to be the safest place in the house to shelter in-place for the duration.
The house plans were done by a registered architect and a structural P.E., both sealed the plans. "If you could get it up there, you could store an automobile," the P.E. said. I have motorcycle parts and bicycles up-there.
Pic. #3 shows a storage platform above the OH doors, and the luminaires are located below the OH door track. You have illumination whether the OH door is open or is closed. The storage platform holds holiday decorations, empty bins, and such.
