Walls should have been reinforced with wood blocking at the time of construction, in the bath tub, shower and toilet areas . Unfortunitly, this is usually not the case. It can be costly to remove and replace your wall finish and install wood blocking. Although his may be a requirement in order to meet ADA specifications, home owners can choose an alternate mounting method, depending on individual requirements. Bars can be mounted directly to wall studs, vertically or at an angle to match existing stud spacing and will work if the studs happen to be located where you need them.
Horizontal installation can present a different problem.
We find that stud spacing can be at random in the bathroom, especially around the toilet area. In existing conditions, stud spacing and bar size may not match. There are alternative methods of installation that can be considered. For drywall surfaces that are in good condition, bars could be installed using toggle bolts or other heavy duty fasteners. We don't recommend this application because you're relying on the strength of sheetrock.