For a drop-in tub to be safely installed and functional, proper support is required underneath. Typically, a wood surround supports the tub, along with added materials such as cement or insulation ...

It's more difficult to install an undermount tub than a drop-in. "It has to sit absolutely level on the subfloor," says Khiel. "Framing for the surround is done right up to the height of the tub." ...