01How the plumbing runs
Most rowhouses follow a similar logic: water comes in low at the front, waste leaves low at the front, and a vertical stack connects every bathroom and kitchen to the roof vent. The details vary a lot between houses, especially after renovations.
- Cold water
- Hot water
- Drain / waste / sewer
- Vent
- 1City water main, maintained by NYC DEP
- 2Water service line, owned by the property owner. In older houses it may be lead or galvanized
- 3Main shutoff valve and water meter in the cellar: know where yours is
- 4Water heater or boiler with a domestic hot-water coil
- 5Cast-iron soil stack: common in original work, and can crack, scale or rust through
- 6Vent through the roof: lets the drains breathe and protects trap seals
- 7House trap: a U-shaped trap on the building drain, a frequent clog point in older houses
- 8Fresh-air inlet: a small vent near the front wall or under the stoop that serves the house trap
- 9Building sewer: owner-responsible, running under the sidewalk to the main
- 10City sewer main (in many areas a combined storm-and-sanitary sewer)
Schematic and not to scale. Many houses have been altered; some have rear sewer connections, two stacks, or no house trap.
02What you'll typically find
| Component | Often found | Watch for |
|---|---|---|
| Water service line | Lead in many older houses; copper or other materials if replaced | Lead or unknown material: check the NYC DEP map |
| Supply piping | Galvanized steel or brass in original work; copper or PEX from renovations | Low flow, rusty water, leaks at old-to-new transitions |
| Soil & waste stack | Cast iron with lead-and-oakum joints | Rust-through at the bottom of horizontal runs, cracks, scale |
| House trap + fresh-air inlet | In the cellar near the front wall | Recurring main-line clogs; sewer smell near the inlet |
| Building sewer | Cast iron or clay running under the sidewalk | Roots, offset joints, sagging sections |
| Hot water | Gas or oil boiler with tankless coil, or a separate water heater | Inconsistent temperature; heater near end of life |
| Cellar drains | Floor drain tied to the building drain | Backups during storms; dry trap releasing odor |
Original cast-iron drain lines in a cellar. Rust and heavy scale are common in century-old houses.
03Common problems
- Main line clogs at the house trap: every fixture slows, and the cellar floor drain backs up. See sewer backup.
- Leaks from old cast iron: often at the base of the stack or along horizontal runs in the cellar ceiling.
- Low pressure upstairs: galvanized supply pipes narrow inside as they corrode. See low water pressure.
- Frozen pipes on exterior walls, in unheated rear extensions and in hose bibs.
- Leaks at transitions where renovation copper or PEX meets original pipe.
04Planning a renovation
- Camera-inspect the stack and building sewer before you finalize the budget.
- Check the service line material (DEP map plus a visual check) and decide whether replacement belongs in this project.
- Decide on supply piping: replacing remaining galvanized is often easiest while walls are open.
- Find out the permit path early. In NYC, plumbing is performed by or under a Licensed Master Plumber; larger scopes need drawings from an engineer or architect. Landmark districts may affect exterior work such as new vents or meters.
- Plan access: add cleanouts and access panels for the next person who has to work on it.
05Who's responsible for what
In New York City, the owner is generally responsible for the water service line and the building sewer all the way to the city mains, including the portion under the sidewalk and street. DEP maintains the mains. In a house with a rental unit, the owner is also generally responsible for repairs in the tenant's apartment. Hoboken and Jersey City owners should confirm the split with their water and sewer utility.
06Frequently asked questions
What is a house trap, and why does mine keep clogging?
A house trap is a U-shaped fitting on the main drain, usually in the cellar near the front wall, with a fresh-air inlet that vents to the sidewalk or under the stoop. It was designed to keep sewer gases out, but its shape collects debris, so it is a common clog point in older New York houses. Whether to keep, clean or remove one is a code question for a NYC Licensed Master Plumber.
How can I tell if my water service line is lead?
In NYC, DEP publishes an online map of service-line material by building. A plumber can also look at where the line enters the cellar: lead is dull gray, soft, and shows a shiny silver scratch. If the material is lead or unknown, see our lead service line guide.
Should I replace all the cast iron during a renovation?
Not automatically. Cast iron can last a long time; problems usually show up as rust-through at the bottom of horizontal runs, cracks, or heavy scale. A camera inspection before the walls are open, and again once they are, gives you evidence to decide section by section. If walls and floors are opening anyway, replacing badly deteriorated sections at the same time often avoids reopening finished work later.
Do I need a permit to repipe a brownstone?
In NYC, repiping is plumbing work performed by or under a Licensed Master Plumber, typically filed with DOB through a Limited Alteration Application, or with drawings by an engineer or architect if the scope goes beyond limited alteration. Landmark districts can add requirements for exterior work. See NYC plumbing permits explained.
07Related
- Pipe materials, comparedCast iron, galvanized, copper, PVC, PEX
- Pipe repair & repipingService
- Sewer line repairService
- Brooklyn plumbing guideArea
- Compare building typesYour building
Sources & review
Last reviewed . General information, not legal or engineering advice. Rules change and individual buildings differ.