First time posting here, as I haven't been able to find this specific question answered anywhere.
I'm a novice and halfway through a garage storage project, and just discovered that I have double-layer drywall, 1.25 inches of gypsum from surface-to-stud. The wall-mounted shelf units I designed (now on their 3rd redesign) are 48" wide and heavy, built mostly with 2" x 10"s. I want them to be solid enough to support a few hundred lbs each. The shelves are structurally solid, but I'm concerned about mounting them.
I planned to use 3/8" x 4" lag bolts to mount the cleats through the drywall into the stud. 4" bolt - 1.5" cleat - 0.5" (assumed)drywall would leave 2" threaded into the stud. I'm concerned now that with the lag bolts basically unsupported through 1.25" of drywall between the cleat and the stud, the bolts may fail under enough weight. I've researched shear-strength for lag bolts, but does that strength rating take into account an unsupported section in the middle of the bolt?
The wall is framed with standard 16" spacing between studs, and the house was built in 2006. The highest shelf will be 70" off the ground, and the garage ceiling is 14' high. I'm hesitant to use lag bolts any thicker than 3/8" for the sake of not chewing through a third of the width of the studs.