A pipe that burst
Household pressure pushes several gallons a minute through a half-inch line, and it does not stop to consider what is downstream. Catching it inside ten minutes costs you a section of drywall. Catching it after an afternoon at work costs you the floor, the subfloor and whatever was stored below.
- 1 The ceiling stain. It measures the ceiling, not the leak. Water travels along a joist before it drops.
- 2 A burst supply line. Pressurized, so it runs until somebody closes a valve, and it runs downward.
- 3 A frozen line. The exterior wall is where the pipe meets the cold, and where it splits.
- 4 The washer hose. Rubber under constant pressure, and a standpipe that overflows quietly.
- 5 The water heater. It goes at the bottom of the tank, usually while the house is empty.
- 6 Groundwater and backup. Water pressing on the wall, and a floor drain that reverses when the combined sewer fills.
The main shut-off, before anything else
In most Maryland basements the main shut-off is on the street side of the foundation wall, near where the service enters, usually within a few feet of the meter. It is worth knowing where it is before you need it, and worth turning it once a year so it does not seize.
When the interior valve will not seat, common on the older stock across Baltimore City and the inner suburbs, the utility can close the curb stop at the property line. Make that call first and keep working on the valve while you wait, rather than the other way round.
Why the wall gets opened even after it stops
A closed wall cavity is a container, not a drying space. Batt insulation holds the water against the framing, the bottom plate draws it along the floor, and the humidity inside stays near saturation for weeks, longer in a Maryland summer than almost anywhere north of here. Buttoning the wall up over wet studs is precisely how a plumbing bill turns into a remediation bill by the autumn.
What the pipe is made of, and what that predicts
A burst is rarely random, and the material tells you a good deal about what to expect next. Galvanized steel, still in service in pre-war rowhouses and older county stock, rusts from the inside until the wall of the pipe is thin enough to split, usually along a horizontal run. Copper fails differently, through pinholes: a weeping spot the size of a pencil point that has been dampening a joist for months before it opens. And polybutylene, the gray plastic supply piping installed widely between the late seventies and the mid-nineties, tends to fail at its fittings and is worth identifying on sight in any house of that vintage.
The reason it matters at the moment of the flood is simple: a pipe that split because the whole run is at the end of its life is very likely to do it again, somewhere else, before the drywall is back on. That changes the order of the work. Drying and rebuilding around a plumbing system that is about to fail a second time is how a household ends up paying to open the same wall twice in a year.