Plumbing is two systems in one: clean water in under pressure, and waste out by gravity, with vents that let drains breathe. Both have rules for a reason. A supply leak floods a floor. A poorly vented drain lets sewer gas into the house. A badly installed water heater can be dangerous. That's why many towns require permits for most plumbing beyond small repairs.
This guide helps you separate repairs from permit-triggering work and shows what to decide, measure and ask. General guidance only. Check with your local permit office, and hire licensed pros for gas work and anything you're not sure about.
What usually needs a permit
- Water heater replacement. Many towns require a permit even for a like-for-like swap, because venting, gas connections and relief valves matter.
- Moving or adding fixtures. A new bathroom, a relocated sink, a laundry hookup.
- New drains, vents or supply lines.
- Gas piping of any kind. Treat gas as licensed-pro work.
- Sewer or septic connections and repairs to the building sewer.
- Backflow devices and irrigation tie-ins.
- Repiping a house.
What often doesn't
Fixing a leak, clearing a clog, replacing a faucet or a toilet in the same spot, or swapping a shut-off valve are commonly treated as repairs. But some towns, and some situations, require more. When in doubt, ask.
Who is allowed to do the work
Some states let homeowners do plumbing in their own single-family home with a permit. Others require a licensed plumber. Gas work is often restricted further. Find out before you start.
What to decide first
- Scope. A short list of what changes.
- Water heater type. Tank or tankless, gas or electric or heat pump. A fuel or type change can bring venting, electrical or gas line changes.
- Fixture layout. Sketch before and after if anything moves.
- Access. Can you reach the drain lines from a basement or crawlspace, or will walls and floors need to open?
What to measure and note
- Distances from new fixtures to the nearest drain stack and vent.
- Pipe sizes and materials where you can see them.
- For water heaters: the existing unit's capacity, fuel, venting type and the space around it.
- Whether the home is on public sewer or a septic system, and public water or a well.
Sully's materials list covers pipe, fittings, valves and supports sized from confirmed runs, with a waste allowance, and flags anything that should be sized by a plumber.
Questions to ask your permit office
- Does this work need a plumbing permit? A gas permit?
- Can I do this as the homeowner, or does it need a licensed plumber?
- Which inspections are required, and when? Underground, rough-in, final?
- For a water heater: what do you check at inspection?
- Do you need a fixture list, an isometric sketch, or product sheets with the application?
- If I'm on septic, does adding a bathroom need a separate review?
Common reasons plumbing work fails inspection
- Drains without proper slope or venting.
- Walls closed before rough-in inspection.
- Water heater relief valve discharge piping not installed correctly.
- Gas connections done without a permit or proper testing.
- Joists or studs cut beyond what's allowed to fit pipes.
Septic systems and wells
If your home is on a septic system, adding a bathroom or a bedroom can change what the system is expected to handle, and septic systems are often overseen by a county or state health agency rather than the building department. Wells have their own rules about distances from septic components and protection from contamination. Sully looks for the agency that oversees these where you live and labels the source. If it can't find one, the report says so.
Old pipes and hidden problems
Older homes may have galvanized steel supply lines that have narrowed with corrosion, cast-iron drains near the end of their life, or, in some very old homes, lead service lines. If you're opening walls anyway, it can be the right time to replace them. Your water utility can often tell you what material the service line is.
Water heaters, in a little more detail
The water heater is the plumbing job homeowners ask about most, so it's worth a closer look. A tank water heater has a temperature and pressure relief valve that has to discharge somewhere safe, usually through a pipe that ends near the floor or to an approved location. Gas units need proper venting and a supply of combustion air, and switching between venting types can mean changes to the chimney or a new vent through the wall. Some areas require seismic strapping or an expansion tank. Switching to a heat pump water heater changes the electrical needs and needs space and airflow around the unit. None of this means you can't do it, but it's why so many towns want a permit and an inspection even for a straight swap. Bring the old unit's label details and the new unit's installation manual when you talk to the office.
Planning the shut-off
Before any plumbing work, find the main water shut-off and make sure it actually works. Old gate valves often won't close fully. Know how to shut off the water heater's gas or power too. If the main shut-off is stuck, a plumber can replace it, and that's a good first job to do before anything else.
Do it yourself or hire a pro?
Faucets, toilets, and simple repairs are common DIY work. Water heaters, gas, new drains and anything that touches the main sewer or septic are where licensed plumbers earn their keep, and where many towns require them. Sully's report gives a plain recommendation for your project.
How Sully helps with plumbing
Sully asks what's changing and where, then reads your town's pages first, then county and state, then the model code, and labels each rule with its source. The report covers whether your town says a permit is needed, who may do the work if published, the inspections your town lists, and who to call. If something isn't published online, the report says so and points you to the office.
Related reading: Remodeling a bathroom and DIY or hire a pro?.