Many of our school and performance space projects have a stage that is tall enough that the client will inevitably ask what we can do to access the space under the front of the stage for storage. That space can be used as long as the following items are addressed.
First, the code requirements in the International Building Code require that any space under a stage used for storage or any other purpose besides equipment, wiring or plumbing the floor assembly must be 1-hour fire rating which generally will mean two layers of fire rated gypsum board.
Second, remember that the structure holding up the stage has depth, so the space under your 36″ high stage may only be 24-28″ tall. Generally any stage under 3o” high won’t have enough height to be useful.You also need a series of posts to hold up the stage and those need to be coordinated with the openings to the space.
Finally, you can practically only access what you can grab from the front. Having a space 20′ deep and only 2′ high is unlikely to be very useful. In most cases we end up designing a chamber between 4′ and 10′ deep. This chamber is built with the 1-hour lid and a 1-hour wall at the back and sides.