||09-11-2013 11:04 AM
WELCOME Annie ... You are in good hands here. Lots of experts and experience to clear up your concerns and give you good advice.
How do you know there is a void?
Can you post pics?
Neal is correct ... voids under tubs allow the plumbers to geain access ... and you might need it to replumb the new tub. Standard tub is 5' long (60") ... unless you are planning a large jacuzzi, you don't have to rip out the wall.
Updating the wall and floor tile is a good decision. Just make sure the shower wall is water tight by using Hardie board and sealing membrane or something just as good. DO NOT use green srywall because it is NOT waterproof.
Help is on the way!