A platform bathtub is enclosed in a framed platform and surfaced with tile, wood, or other finishing material. The project may require reinforcing existing floor framing in addition to the construction skills and tools to build the platform and plumbing know-how and tools to install the unit, its water and drain lines and faucets. If you are so gifted, follow the tub manufacturer’s directions for the wiring and plumbing requirements and use these guidelines for building a platform.
Follow the tub manufacturer’s suggestions and design a platform that’s at least a foot wider and longer than the tub and high enough to support it above the existing floor. Build the framework for the platform from 2 x 4s and 3⁄4-inch exterior-grade plywood, using nails and deck screws to fasten them together. The height of the platform should allow for the plywood decking plus the thickness of backerboard, thinset mortar, and tile and allow a 1⁄4-inch expansion gap between the tub and the finish material. If you’re installing a whirlpool tub, make an opening in the framework for an access panel for the pump and drain.
Constructing the platform for a tub isn’t difficult, but it requires accurate measuring and cutting. This project is very straightforward for a carpenter, so you may be well served to hire out this phase.
Check the height of the platform that your tub requires and calculate the height of the platform wall studs.
For example, if the tub requires a 36-inch-high platform, the studs should be cut to 31 3⁄4 inches. This length allows for the thickness of the top and bottom 2-x-4 plate, the 3⁄4-inch plywood, backerboard, mortar, and tile.
Nail the studs to the top and bottom plates to form the walls for the platform.
Secure the wall framework to the floor with nails, and use deck screws to cover the framework with plywood to make the deck.
Use a jigsaw to cut an opening in the deck for the tub, either by using the template provided by the manufacturer or after carefully marking the dimensions for the rough opening.
Follow the faucet manufacturer’s instructions for measuring and marking the rough-in locations for supply pipes.
Drill the holes in the deck and then rough in the water supply and drainpipes.