Code Stories
Why the plumbing code says what it says
Every rule in 248 CMR is there because something went wrong without it. Learn the reason and the rule stays with you, on the exam and on the job. Each lesson starts with the current Massachusetts rule, then explains the hazard behind it and the history that put it in the code.
- Traps and Trap Seals
Every fixture drains through a trap that holds a plug of water (the trap seal) between the room and the sewer. In Massachusetts each fixture trap must hold a li
- Venting: Why Vents Exist
The drainage system has to be open to outdoor air through vents so that air can flow in and out of the pipes. That protects every trap seal from being sucked ou
- Trap Arm Length (Distance from Trap to Vent)
The trap arm is the fixture drain from the trap weir to the vent fitting. Massachusetts limits its developed length by pipe size (248 CMR 10.16(10) Table 1): 1-
- Drainage Fixture Units (DFU): Hunter's Probability Method
Drain and vent pipes are sized by adding up fixture units, a relative load weight assigned to each fixture type, and reading the allowed pipe size from a table.
- Cleanouts: Spacing and Changes of Direction
Massachusetts requires accessible cleanouts at or near the base of every waste, soil and storm stack, at each change of direction of the building drain, and at
- Backflow, Cross-Connections and RPZ Testing
Drinking-water piping must never be connected to anything that could push or siphon contaminated liquid back into it, unless an approved backflow preventer suit
- Air Gaps
Where a potable water outlet discharges into a fixture or tank, there must be an unobstructed vertical air gap, measured from the lowest end of the outlet to th
- Water Heater T&P Relief Valves
In Massachusetts, all storage water heating equipment capable of heating water above 212°F needs a properly sized T&P relief valve (248 CMR 10.14(6)(f)2). It go
- Hot Water: Hot Enough for Legionella, Safe Enough for Skin
Massachusetts sets hot water temperatures in 248 CMR 10.14(5). Domestic hot water in residential buildings must be at least 120°F and may not exceed 130°F; fixt
- Maximum Flush Volume: 1.6 gpf and the Energy Policy Act of 1992
Massachusetts limits toilets to a maximum of 1.6 gallons (6.0 liters) per flush (248 CMR 10.10(2)(f)) and urinals to a maximum of one gallon (3.8 liters) per fl
- Lead-Free Solder, Pipe and Fittings
Anything that carries drinking water must be 'lead free' as federally defined: solder and flux no more than 0.2% lead, and pipes, fittings and fixtures no more
- Grease Interceptors (FOG)
Massachusetts requires interceptors to receive discharge from all fixtures and equipment that may produce grease-laden waste wherever food is prepared (248 CMR
- Gas: Sediment Traps (Drip Legs)
At the inlet to most gas appliances, the gas supply drops into a tee with a capped nipple below it (the sediment trap) before turning to the appliance. It catch
- Gas: CSST Bonding and Lightning
Massachusetts rewrote the national CSST bonding rule. 248 CMR 5.07(5) deletes NFPA 54-2012 section 7.13.2 and replaces it: CSST systems 'shall be bonded in acco
- Gas: Combustion Air and Carbon Monoxide
Fuel-burning appliances must get enough air for complete combustion, for draft-hood dilution, and for ventilation, either from the room (if it is big enough and
- Gas: Sidewall Vent Terminals and Massachusetts CO Rules (Nicole's Law; 248 CMR 5.09(7) and 5.12(6))
Two current 248 CMR amendments to NFPA 54 apply, plus Nicole's Law. (1) Signage, 248 CMR 5.12(6), which adds NFPA 54 12.9.7: whenever a through-the-wall vent is
- Licensing: Why Massachusetts Licenses Plumbers (and Why Apprenticeship Hours)
In Massachusetts you may not do plumbing work without a state license (apprentice, journeyman, master), issued by the Board of State Examiners of Plumbers and G