The shower pan surrounds the drain under the shower stall and above the subfloor. This protects wooden subfloors from water damage. This shower pan should be installed over the subfloor on top of a 1/2-inch thick layer of mortar or plaster. The top lip of the shower pan at the entrance to the shower is the threshhold. This is the raised portion of the shower base that directs water in the bottom of the shower to the drain. When entering the shower, you step over the threshhold, which should be between 2 and 9 inches high, according to R. Dodge Woodson in "2006 International Plumbing Codes Handbook." All-in-one shower stalls can be installed flush over a concrete subfloor.
The total height of the shower allows for most people to comfortably stand in the shower. Showers should not be lower than 70 inches high as measured from the drain to the top of the shower, according to the "2006 International Plumbing Codes Handbook" by R. Dodge Woodson. Taller showers will allow for higher placement of the showerhead. The measurements for the interior width and length cannot be less than 30 inches in either direction. This provides for a minimum area inside the shower of 900 square feet.
The height of the showerhead keeps you from bumping your head into the fixture and causing injury. Commonly this height is higher than the minimum height for a shower. "Fine Homebuilding" in "Renovating a Bathroom" notes that 6-feet 7-inches is the typical height for installing a showerhead, and the curtain rod for a shower is set just 1 inch below that.
The control knob for the water needs to be low enough for all members of the family to easily reach it. The height recommended in "Ultimate Guide to Plumbing: Complete Projects for the Home" is 48 inches from the floor of the shower. A range of heights from 42 to 48 inches from the base is suggested by Charles G. Wing in "Ortho's Home Improvement Encyclopedia Problem Solving A to Z." This control knob must also regulate the water temperature flowing through the shower to below 120 degrees Fahrenheit.