Things You'll Need
2-inch by 4-inch lumber
1/2-inch CDX moisture-resistant plywood
1/2-inch drill bits
Hole saw drill bits
Standard recessed bathtub enclosures are practical for shower installation yet predictable and visually unappealing. Custom platform bathtub installation is preferable when a shower is not necessary or can be installed separately. Corner bathtubs not only enhance the aesthetic appeal of the bathroom but also make good use of bathroom space and improve the flow of the room design. Although custom corner-bathtub installation may seem complicated, most do-it-yourself enthusiasts can easily build a corner frame for a standard or over-sized bathtub.
Measure and cut two boards to the length of the bathtub plus 6 inches. Place one of these boards broadside down along one wall, with the end set firmly into the corner, to form the base plate of the first rear wall of the tub frame. Nail the board firmly to the floor joists, and label the board "wall 1." Set the other board aside; label it as "top plate wall 1."
Measure and cut two boards to the length of the bathtub plus two and a half inches. Place one of these boards broadside down along the other wall, with the end set firmly into the corner against the first board, to form the base plate of the second rear wall of the tub frame. Nail the board firmly to the floor joists and label the board "wall 2." Set the other board aside; label it as "top plate wall 2."
Measure and cut four boards to the width of the bathtub plus two and a half inches. Place two of these boards broadside down perpendicular to the walls, with the end set firmly against the outer ends of the base plates for walls 1 and 2. Nail the boards firmly to the floor joists and label the boards "wall 3" and "wall 4." Set the other boards aside; label them as "top plate wall 3" and "top plate wall 4."
Place a board across the ends of walls 3 and 4, mark the boards to create a diagonal line flush with the ends of these walls, and cut the board for the base plate of wall 5. Use this board as a template to cut the top plate for wall 5. Set the base plate for wall 5 into place and nail it firmly to the floor joists. Label the other board as "top plate wall 5" and set it aside.
Measure the height of the underside of the bathtub lip, allowing space for drain pipes, and subtract three inches. Cut approximately 24 boards to this length. Nail these boards to the base plates to form the vertical supports for the tub walls. Nail one board flush to the end of each base-plate board, and nail additional boards spaced every 16 inches along the base-plate boards. Nail the cap-plate boards to the tops of the walls to complete the frame wall construction.
Measure and cut plywood to clad the exterior of walls 3, 4 and 5 -- and then nail the boards into place. Measure and cut plywood to clad the top of the frame and nail the board into place.
Caulk all of the seams in the platform and allow them to dry thoroughly, according to the caulk manufacturer's recommendations.
Trace the bathtub basin onto cardboard and cut out the tracing to create a template approximately one inch larger on all sides. Place the template onto the platform and trace around it. Use the drill to create a hole to start the jigsaw cut, and use the jigsaw to cut out the hole for the bathtub.
Use hole saws to cut holes in the platform for faucet hardware.
Finish the platform with tile or other material before installing the bathtub.