Locate then measure the area around the drain where you want the wheelchair shower pan to be located in the floor. You will need a space that is at least 30 inches out from the wall and 60 inches wide to accommodate a standard wheelchair. Mark the perimeter of this area with masking tape.
Measure approximately 2 feet out from the side of the marked area where you want to place the shower’s entrance. Mark this 2-foot area of the floor separately with masking tape.
Cut into the floor with a circular saw to remove the floorboards in the area marked for the shower pan if the floor is wood and trim down the joists inside the marked area by 3 inches. Use a jackhammer or sledgehammer to break up the floor if it is concrete or cement to a depth of 3 inches.
Measure the spaces between the floor joists that you trimmed down, if you're working with a wood floor, and cut wood boards that sit at the same height as the trimmed joists to this length. For example, if you trimmed down an 8-inch joist to 3-1/2 inches, use 3 1/2-inch boards. Cut enough boards so that you have one to place every 6 inches between the joists and secure the boards with wood screws drilled in at a 45-degree angle to pass through the cross-pieces and into the joists.
Cover the new wood structure of a wood floor with 1/2-inch plywood. Screw the plywood into the joists to create a surface for the shower pan. Remove the broken-up pieces of concrete or cement inside of the marked area on the floor to prepare the shower pan surface.
Add enough water to concrete mix to make a thick, just spreadable, material. Use a spade to spread the concrete in the shower pan area so that the concrete sits roughly 1-inch high around the drain and slopes upward toward the edges until it sits level with the surrounding floor. Use a level to check the slope of the concrete surface then wait for the concrete to fully dry.
Remove the nails from the floorboards in the second 2-foot section of a wood floor where you want to place the shower entrance and take up the floorboards. Spread mortar between and over the joists to build the floor back up and create a slight slope to the section of floor and angled down toward the shower to make a small hump in the floor. If the floor is concrete or cement, build the floor up at a slope in the same manner to create a small hump approximately 2 feet out from the shower to help keep water in the shower area.