General Regulations, Definitions, and Administration
The legal framework
Michigan enforces the International Plumbing Code as amended by the state, adopted through local enforcing agencies that issue permits and perform inspections. Know the admin basics: a permit is required before a plumbing system is installed, altered, replaced, or extended; work must be performed by a licensed plumber (with limited owner-occupant exceptions where local ordinance allows); and inspections are required at rough-in - before piping is covered - and at final. The code official decides what is approved; the contractor does not.
Definitions that generate questions
Questions are often written straight from Chapter 2. Accessible means reachable for service without damaging the building. Readily accessible means reached quickly, without climbing over or removing obstacles, without a portable ladder, and without tools. A cleanout behind a screwed access panel is accessible but not readily accessible. Approved means accepted by the code official; listed means published by an approved testing agency such as UL, NSF, or CSA. Flood level rim is the edge of the fixture from which water overflows - the reference point for air gaps, backflow devices, and vent height. Developed length is measured along the centerline of pipe and fittings; it drives both vent and gas sizing. Cross-connection is any actual or potential link between potable and nonpotable water.
Rule of thumb
If a person must operate or service it routinely - a valve, cleanout, trap, or air admittance valve - the code wants it readily accessible. If it only needs occasional service behind a panel, accessible is enough.