MI Plumber cheat sheet

A plumbing permit must be obtained before installing, altering, replacing, or repairing a plumbing system; ordinary minor repairs defined in the code are exempt.

"Approved" means accepted by the code official, typically supported by listing and labeling by a recognized third-party testing agency.

The building drain ends 30 inches outside the exterior wall; the building sewer begins at that point and runs to the public sewer or private sewage disposal system.

One drainage fixture unit (dfu) represents roughly 1 gallon per minute of probable discharge; water supply fixture units are derived from Hunter's probability curve.

No fixture drain may be smaller than 1-1/4 inches, and no drainage pipe may be smaller than the outlet of the fixture it serves.

The code official may require plans, specifications, and sizing computations for systems exceeding the thresholds stated in the code.

Plumbing work must be performed by a licensed plumber under a licensed plumbing contractor, with rough-in and final inspections required before concealment and occupancy.

Alternate materials, methods, and equipment require written approval from the code official before installation.

Horizontal drainage slope is 1/4 inch per foot (2 percent) for pipe 2-1/2 inches and smaller and 1/8 inch per foot (1 percent) for pipe 3 inches and larger.

Horizontal drainage pipe is supported at intervals from the code table (commonly 4 feet for plastic and 5 feet for cast iron); stacks are supported at the base and at each story.

A horizontal drain turning 90 degrees uses a long-sweep fitting or two 45-degree bends; a horizontal branch enters a vertical stack through a sanitary tee.

Cleanouts are required at the upper end of horizontal drains, at the base of each stack, at aggregate direction changes of 135 degrees, and within 5 feet of the building sewer.

Typical fixture units: water closet 3, lavatory 1, bathtub or shower 2, kitchen sink 2, washing machine 2, dishwasher 2, 2-inch floor drain 2.

A horizontal drain joining another horizontal drain uses a wye fitting with a 1/8 bend (combination); tees are not permitted in the horizontal position for drainage.

Building drains and building sewers serving water closets are minimum 3 inches and are sized by total fixture units from the code tables.

A backwater valve is required where the building drain is below the flood level rim of the next upstream manhole and must remain accessible.

Every trap must be protected by a vent, and the vent must connect within the maximum trap arm length permitted for that pipe size.

Trap arm limits at 1/4-inch slope: 1-1/4 inch = 5 feet, 1-1/2 inch = 6 feet, 2 inch = 8 feet; at 1/8-inch slope 3 inch = 12 feet and 4 inch = 16 feet.

A vent may not be smaller than 1-1/4 inches and may not be smaller than one-half the diameter of the drain it serves.

A dry vent must rise vertically, or at no more than 45 degrees from vertical, until it reaches at least 6 inches above the flood level rim of the highest served fixture.

A vent terminal must extend at least 6 inches above the roof, or 7 feet where the roof is used for purposes other than weather protection; in frost-closure areas the terminal is increased to 3-inch pipe.

Open vent terminals must be located at least 10 feet from windows, doors, and outdoor air intakes.

A wet vent may serve only fixtures on the same floor and must be at least 2 inches where it drains a water closet.

Air admittance valves are permitted only where the code allows, must be installed above the fixture flood level rim, and must remain accessible.

Static pressure above 80 psi requires a pressure reducing valve; a minimum residual pressure of about 8 psi is required at fixture outlets under flow.

Minimum fixture supply sizes: water closet 1 inch, lavatory 3/8 inch, sink 1/2 inch, bathtub 1/2 inch, shower 1/2 inch.

Horizontal water pipe is supported at intervals from the code table (typically 12 feet or less); vertical pipe is supported at each floor.

Backflow protection: air gap for severe hazards, reduced-pressure zone assembly for high hazards, and vacuum breakers for low hazards; testable assemblies require periodic testing.

Water heaters require a temperature and pressure relief valve with a full-size discharge pipe flowing by gravity and terminating within 6 inches of the floor or outside the building.

Water service pipe must be buried below the local frost depth and protected from freezing at exposed locations.

The water distribution system is tested tight at not less than the working pressure before piping is concealed.

A main shutoff valve is required on the water service, and drain valves are provided for winterizing the system.

Water closet clearances: 15 inches from centerline to any side wall, 30 inches center-to-center, and 21 inches of clear space in front of the bowl.

A lavatory requires 15 inches from its centerline to a side wall; fixtures must be spaced to allow use and cleaning.

Shower compartments must be at least 30 inches by 30 inches inside, drain through a minimum 2-inch drain, and have a finished curb unless designed as an accessible roll-in shower.

Fixtures must be constructed of smooth, nonabsorbent, corrosion-resistant material and installed to allow cleaning and access to concealed parts.

Each fixture must be provided with an approved water supply, a trap, and a drainage connection sized from the code tables.

Water heater pans are required where leakage would cause damage, with the pan drain discharging by gravity to an approved location.

Handwashing lavatories are required in toilet rooms and food service areas, and drinking fountains may not be located in toilet rooms.

Trap seal depth must be at least 2 inches and not more than 4 inches, measured between the trap weir and the top of the trap dip.

Each fixture must be separately trapped except for listed combinations such as a single trap serving a set of approved fixtures.

S-traps, bell traps, crown vents, traps with moving parts, and traps for fixtures with integral traps such as water closets are prohibited.

A grease interceptor is required for food service establishments and is sized by the code formula or table, with access for cleaning and periodic pumping.

Oil and water separators are required where flammable liquids or petroleum products may enter the drainage system and must be vented per code.

Sand and grit interceptors are required for vehicle service and wash areas, must be accessible, and must be vented.

Corrosive or high-temperature wastes require neutralization or cooling before discharge, and boiler blowdown must not enter a building drain untreated.

Interceptors must be provided with a vent sized and installed per the venting provisions of the code.

Storm drainage must be conveyed separately from sanitary drainage unless the authority having jurisdiction approves a combined connection.

Roof drains and leaders are sized from code tables using the roof area served and the 100-year, one-hour rainfall rate for the location.

A roof with a parapet that uses roof drains requires a secondary drain or scupper set at least 2 inches above the primary drain or low point.

Storm drainage pipe follows the same slope rules as sanitary: 1/4 inch per foot for 2-1/2 inches and smaller, 1/8 inch per foot for 3 inches and larger.

Vertical leaders and conductors must be supported at each story and at the base, and must be anchored to resist wind and water movement.

Subsoil and footing drains must discharge to an approved location and may not be connected to the sanitary building sewer unless specifically approved.

Sump pumps discharge to a storm sewer, splash block, or approved drywell; they may not discharge into the sanitary sewer unless permitted.

Fall in inches = slope in inches per foot multiplied by run in feet; 1/4 inch per foot over a 20-foot run gives 5 inches of fall.

45-degree offset: travel = offset x 1.414, and offset = travel x 0.707. At 22.5 degrees travel = offset x 2.613; at 60 degrees travel = offset x 1.155.

Pressure to head: psi = feet of water divided by 2.31, and feet of head = psi x 2.31; a 10-foot column equals about 4.33 psi.

Gallons contained in a pipe = 0.785 x D-squared x length divided by 231, with diameter and length measured in inches.

Roof runoff in gallons per minute = roof area in square feet x rainfall rate in inches per hour x 0.0104.

A bathroom group of water closet, lavatory, and bathtub or shower totals 6 drainage fixture units.

Water heater recovery gallons per hour = (Btu/hr input x efficiency) divided by (8.33 x temperature rise in degrees F).

Bend designations: 1/16 bend = 22.5 degrees, 1/8 bend = 45 degrees, 1/6 bend = 60 degrees, and 1/4 bend = 90 degrees.

Excavations 5 feet deep or more require a protective system such as sloping, shoring, or a trench shield, and a competent person must inspect the excavation daily.

Spoil and materials are kept at least 2 feet back from the trench edge, and a ladder must be within 25 feet of lateral travel in trenches 4 feet or deeper.

Portable ladders are set at a 4-to-1 base-to-height ratio and extend at least 3 feet above the landing surface.

Compressed air testing of drainage piping is limited to about 5 psi because stored energy in air can cause violent pipe failure.

Soldering requires lead-free solder and approved flux; tubing must be reamed and cleaned, flux residue removed, and combustibles protected during hot work.

Solvent cement must match the plastic pipe material, primer is applied before cement, and the joint must cure before pressure testing.

Plastic drainage pipe is supported at 4-foot intervals with approved hangers that do not crush or deform the pipe.

Entry into vaults, pits, and sewers requires a confined space permit, atmospheric testing, an attendant, and a rescue plan.

Gas piping is sized by the longest-length method using total connected load in Btu/hr, gas specific gravity, and available pressure drop from the code tables.

Minimum gas piping size is 1/2 inch; concealed gas piping may not contain unions and may not pass through ducts, chimneys, or elevator shafts.

A sediment trap (drip leg) is required at each appliance, and a shutoff valve must be installed within 6 feet of the appliance in the same room.

Gas piping must be bonded to the premises grounding electrode system, and corrugated stainless steel tubing must be bonded per the manufacturer's instructions.

Gas piping is leak tested with air or inert gas at 1.5 times the working pressure, but not less than 3 psi, for at least 10 minutes.

Flexible appliance connectors may not exceed 6 feet, may not pass through walls, floors, or ceilings, and may not be concealed.

Clearance to combustibles is 6 inches for single-wall vent connectors and 1 inch for listed Type B vent.

Combustion air for a confined space is provided by two permanent openings or by 50 cubic feet of volume per 1,000 Btu/hr of input where infiltration is used.