Good Morning; just a few facts for shower pans:
As of 2017 there are 2 codes for shower pans, one residential & one Commercial, they are as follows:
Residential Section P-2709.3 – States that a shower floor must be sloped before the install of a shower pan
Commercial 417.5.2 States the same as above
There is only ONE exception & that is the floor must have a minimum of 2″ recessed concrete floor & only an exception when the recess floor is poured at the same time as the surrounding floors.