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How to Rough Frame a Drop-in Bathtub

Kenneth Crawford

Drop-in tubs require a box frame. The flange of the tub rests on all four sides of the frame. Rough framing for a drop-in bathtub is much like framing for a wall. There is a top and bottom board with studs between them.

Take accurate measurements of the tub to ensure you have a sufficient box opening for a secure installation.

  1. Measure the length of the tub from end to end with a tape measure. Subtract 1 1/2 inches from the measurement for your rough-in length. Measure the width of the tub and subtract 1 1/2 inches for the rough-in width. Measure the depth of the tub from the front bottom to the front top of the tub ledge.

  2. Cut four 2-by-4-inch boards to the rough-in length with a circular saw. Subtract 4-inches from the tub height and cut ten pieces of 2-by-4-inch boards to the adjusted tub height.

  3. Lay one of the tub length boards on its edge on a flat surface. Place one of the height boards on its edge on the end of the length board. Drive two 16d nails through the length board and into the height board. Repeat for the opposite end of the length board.

  4. Place a second length board across the top of the two corner height boards. Place a carpenters square across the outside corners to ensure the boards are joining perfectly square. Drive nails through the second length board and into the ends of the height board.

  5. Divide the length by four to get the center marks for each of the supporting height boards. Place marks at the center measurements on both length boards. Set the height boards in between the two length boards and secure them with nails. Repeat the process for the opposing side of the tub frame.

  6. Stand the two side frames up and place a width board in between them on the floor. Place a carpenter’s square around the outside corner to ensure the width board is square with the two sides. Toe-nail the width board into the bottom of the two sides at the end. Repeat for the opposite end of the tub. Toe-nailing is driving the nails into the boards at an angle.

  7. Place two height boards evenly across the width board and toe-nail them in place. Place another width board across the top of the two height boards. Nail the boards together, toe-nailing the ends into the top of the sides. Repeat for the opposite end.