The 2006 International Building Code includes Section 1210 Surrounding Materials which specifies where you need nonabsorbent surfaces.
In toilet and bath rooms you need a smooth, hard, nonabsorbent surface on all walls to a minimum of 6″. This isn’t required at dwelling units. Its important to watch for this one, you can’t get by with a standard 4″ base.
Where you are within 2′ of a urinal or water closet (frequently referred to as wet walls) that material needs to extend to 48″ above the floor. In addition the wall materials must not be adversely affected by moisture. This isn’t required at dwelling units, sleeping units or single toilet rooms not accessible to the public. Where toilet room accessories penetrate the material they need to be properly sealed.
Where you have showers or tub/shower combinations the nonabsorbent material must extend to 70″ above the drain height. Any joints between the tub and shower surround must be waterproofed.
Finally, the section includes one rule that seems a little lost. Toilet rooms can’t open directly into food preparation areas where the food is served to the public.