Where does water from an upper-floor laundry actually go?
Across the floor to the nearest gap, then down. It finds a pipe penetration, a gap at the wall or the edge of the subfloor, drops into the joist bay beneath, and runs along the joists until it reaches a low point, which is often a ceiling in another room entirely.
That is why the ceiling stain downstairs is rarely under the machine. Following the stain upward leads to the wrong hole, so the path is traced with meters from the known source instead.
Where the ceiling below is plaster on wood lath, it also holds the water quietly for a while. The first sign may be a faint ring or a hairline crack long after the joists above have soaked, which is one reason an appliance leak gets underestimated on the day.
What actually fails on a washing machine?
Usually a hose rather than the machine. Rubber supply hoses harden, blister and split at the crimped fittings, and they are under mains pressure all the time, not only during a cycle. Drain hoses work loose from the standpipe, door seals tear, and pumps and drums leak as they age.
The useful habit is to look behind the machine twice a year: feel the hoses for stiffness and bulges, check the fittings are dry, and make sure the drain hose is secured so it cannot jump. Braided stainless hoses and a shut-off you actually use both reduce the odds.
A leak alarm on the floor behind the machine, or a pan under it where the floor allows, turns a flood into a nuisance. On a third floor in a three-family house that is worth more than it costs, since the damage is never confined to your own apartment.
How do you dry a floor and the ceiling below it at once?
By treating them as one assembly. Equipment goes in both rooms, the floor covering above and the failed ceiling material below come out where they hold water, and small openings let air into the joist bay between them. Readings in subfloor, joists and ceiling material decide when it is finished.
Skipping the cavity is the common mistake. A floor can read dry on top and a ceiling can look sound from below while the bay between them stays wet for weeks, which is how an appliance leak becomes a mold job. Air has to move through that space.
In older houses the assembly is plank subfloor, heavy joists and plaster on lath, all of which hold water and release it slowly. Expect the drying to be measured in days and run to readings, as set out under structural drying and dehumidification.
What changes the size of an appliance-leak job?
How long the water ran, how many floors it reached, how much flooring, cabinetry and ceiling has to come out, whether the water was clean, and how awkward the access is. More units involved means more coordination. The price is explained and approved before any work starts.
A hose caught in the first ten minutes on a tiled floor is a small job. The same hose running overnight from a third-floor laundry is a multi-room, multi-unit job with ceilings, cabinets and belongings in it, and the difference is time rather than anything about the appliance.
Building age shows up in both directions: there is often more to save in an older house and it takes longer to dry. If cleanup will disturb old plaster, pipe insulation or flooring, ask about asbestos rules first, and expect any reconstruction to be quoted as separate work.
What should I do the moment I find the floor wet?
Close the valves behind the machine, unplug it if you can reach the cord without standing in water, and stop using it. Move what you can off the wet floor, mop or towel the surface water, and photograph everything before it is tidied away. Then check the room below.
Checking downstairs is the step people skip. Look at the ceiling under the laundry and under the room next to it, feel the walls at the base, and if a neighbour or tenant lives there, knock. Finding it early is the difference between a drying job and a rebuilt ceiling.
Then call, even if the water has stopped. Phones are answered 24/7 and a crew is sent as soon as one is free. The EPA's guidance is that mold generally will not grow if wet materials are dried within 24 to 48 hours, and that window is the reason not to wait and see.