Plumbing

What it is

Plumbing is the water that goes into a house and the waste that comes out. Two halves: supply side (water lines, pressure, fixtures) and drain-waste-vent, which is DWV — drains, sewer laterals, vent stacks that let sewer gas escape through the roof. It’s one of the three MEP trades alongside mechanical (HVAC) and electrical.

Galvanized water lines are common in older houses and they rust from the inside out — kills pressure. In a lot of municipalities, if you have galvanized and you’re doing any renovation at all, they’ll require you to replace them all the way to the city water tap. That’s a cost you need to know before you close.

Why it matters

99% of structural damage traces back to water. Plumbing is where the water originates. Diagnosing plumbing well is diagnosing the whole house. A single bad joint in a wall, slow-leaking for years, rots framing, grows mold, and tanks a sale.

The sewer line scope I always preach: before you buy, $300-500 for a camera scope of the sewer line. Collapsed lines, tree roots growing through the line, negative slope — I’ve bought a house where instead of the sewer line sloping to the city tap it was sloping back toward the house. Every time the toilet flushed it would just come back up. All of those situations lead to the same resolution: replace the whole thing. That’s $10,000 to $40,000 depending on what’s wrong and how long the run is. A sewer tap or street cut can hit $10-15K by itself. That delta alone kills the deal margin on an otherwise cosmetic flip.

And I’ve found subterranean surprises that would have wrecked me had I not lucked out. I once dug a French drain on a property and hit a soft spot in the ground that turned out to be a pit — turned out they’d shot their main sewer line right out into the yard. That was a $40,000 oversight. Always get your sewer lines inspected.

How it shows up

MEP rough happens before framing for a specific reason: plumbers routinely damage framing when they cut for drains. You do framing first, you’re doing framing twice.

Before drywall goes up: water test. Fill all drain lines under pressure. Lines that work fine with flowing waste will sometimes leak when static-filled. Any leak that shows up during the water test is a leak you fix before drywall, not after.

On floor joist notching: there are code limits on how deep you can notch a joist and where along its span. Plumbers commonly over-notch to run drains. An over-notched joist fails structural inspection and has to be sistered or replaced.

Pay schedule: 65% at rough inspection, 35% at trim-out. Never 100% until both inspections clear. Same rule as electrical and hvac. The inspector tells you whether the phase is done, not the contractor.

Related

hvac, electrical, sewer line, sewer tap, permitting, inspections, the gauntlet