Water Leaking Behind a Chicago Wall? What to Do Now
The exterior walls of most Chicago houses are solid brick with furring strips and plaster over them, with no stud cavity in between for a pipe to run through, and that is the single most useful fact to have in front of you when there is a water leak behind a wall. It means the pipe is somewhere other than where the stain is.
Stop the water first. Then work out which wall you are actually looking for.
What to Shut Off Before Anyone Opens Plaster
- Close the main valve. It sits beside the meter where the service comes in through the front foundation wall, and in a two-flat or three-flat there may be one valve for the building and a second one feeding your unit.
- Drain the risers. Opening a laundry tub tap down in the basement pulls the standing column of water to the lowest point in the building rather than leaving it to seep out at the break.
- Cut the power to the affected area at the panel. Older basement receptacles sit low on a masonry wall, and the ceiling fixtures in the room under a leak are directly in the path of the water.
- Turn the water heater down. A tank with no cold water arriving keeps heating what is left in it, so put a gas control on pilot or drop the breaker on an electric unit before you walk away from it.
- Get pictures on your phone of every wet surface, and of the meter dial, before anybody starts opening things up.
If the interior valve will not close, and on a valve nobody has turned in 20 years that is common, the shutoff of last resort is the B-box out in the parkway. That one belongs to the water department and takes a long key, so it is a phone call rather than a job for a wrench.
Solid Brick Has No Stud Cavity, So the Leaking Pipe Is in a Different Wall
The bungalow, the greystone, the worker cottage and the two-flat all share one wall assembly. Load-bearing common brick, two or three wythes thick, so roughly 12 inches of solid masonry. Wood furring strips nailed to the inside face. Wood lath and plaster over the furring. The gap between the plaster and the brick is about an inch deep, which fits nothing, and no tradesman was ever going to route water through an uninsulated masonry wall on purpose anyway.
So the supply lines sit inboard: interior partitions, the chase alongside the waste stack, the wall behind the kitchen sink, and the floor structure itself. When water appears on an exterior wall, it has usually arrived from an interior partition and tracked sideways along the underside of the floor until it found somewhere to come out. Chasing the stain is how people end up opening the wrong bay twice.
The exceptions are the walls that were added later, and they are worth knowing by name:
- rear additions and enclosed back porches, where supply lines cross the coldest square footage on the property
- gut rehabs, where a framed wall was built inboard of the brick and copper or PEX run inside it, which puts the pipe on the cold side of whatever insulation went in
- a bathroom cut into what used to be a pantry or a closet on an exterior wall
One outdoor check is worth the walk. Standard lots leave a gangway of a few feet between buildings, that wall sees no direct sun for months at a stretch, and it is where water sitting inside masonry shows itself: a white bloom on the mortar, or a brick face that has popped off after freezing.
In a Two-Flat, Every Kitchen and Bath Stacks on One Wet Wall
A very large share of the housing here is two-flats, three-flats and courtyard buildings, and the plans repeat exactly floor to floor. Kitchen over kitchen, bath over bath, the whole column hung on a single wet wall around one cast iron stack. That layout decides three things about a leak.
The wet plaster on the first floor is probably being fed from the unit above, so getting access upstairs is part of the repair rather than a courtesy. Sort that out early, because a Saturday leak plus an unreachable neighbor is a lost day. Water inside that chase can also travel down two floors before it shows on any ceiling, which means the highest damp point is where to start looking, not the worst-looking one. And because every unit shares the stack, a drain-side leak turns up as a problem for the whole column while a supply-side leak generally stays with one unit.
Copper Pinholes and Cast Iron Hubs: What Actually Lets Go Here
The city ran its own plumbing code long after much of the country moved to plastic, and for most of that stretch supply meant copper and waste meant cast iron. In an older wall you are almost always looking at rigid copper tube and a cast iron stack, and the two fail in completely different ways.
Copper goes by pinhole corrosion, usually on the hot side and usually within a foot of an elbow, where the flow turns and picks up speed. A pinhole weeps rather than sprays, so plaster can be quietly wet for months and the first sign is a bubble in the paint or a soft patch under a thumb.
Cast iron goes at the hub, the bell where one length receives the next and the joint was packed with oakum and poured with lead. The packing dries and shrinks, and the joint then weeps only while something upstairs is draining. That on-and-off pattern is why the stain seems to appear, dry out and come back with no obvious cause.
There is a third possibility that has nothing to do with a wall. On a great many older properties the municipal water service coming in from the street is well past its design life, and when it fails the sign is a wet patch on the basement slab at the base of the front foundation wall. Same house, different repair. A service replacement is also a permit job the building department signs off on, which is a different piece of scheduling from a wall repair, so it is worth ruling in or out before anyone starts cutting plaster.
Frequently Asked Questions About Brick Walls, Plaster and Water Leaks
The stain is on the outside brick wall. Does that rule out a supply pipe?
It makes a supply pipe in that wall unlikely, because there is no cavity in an original masonry wall for one to sit in. What it does not rule out is water arriving from an interior partition and running along the top of the plaster or the underside of the floor before it drops. Follow the wet upward and inward rather than straight back.
White powder keeps blooming through the paint on the gangway side. Is that a plumbing leak?
That bloom is salt left behind as water evaporates out of masonry, so it proves water is moving through the wall without saying where the water came from. The test is weather. Failed tuckpointing and ground moisture track the rain and dry out in a dry stretch. A plumbing leak keeps the wall damp through a week when nothing has fallen.
The ceiling below only darkens when the tub upstairs empties. Supply pipe or drain?
Drain, almost certainly. A supply line is under pressure every minute of the day, so it leaks whether anyone is home or not. A waste line only carries water while a fixture is discharging, and in these buildings that points straight at the cast iron stack or the branch running to the tub.
The building next door is four feet away. Could their pipe be wetting my wall?
It can happen where two buildings share a lot line closely, though far more of these turn out to be a downspout, a failed gutter or a grade problem in the gangway sending water against the base of the wall. Establish whether your own meter is turning with everything shut off before raising it with a neighbor.
Does a rehab that furred out the brick put pipes in the cold wall after all?
Sometimes, and it is the one situation where a Chicago exterior wall genuinely holds a supply line. A framed wall built inboard of the masonry gives a pipe somewhere to sit, and unless the insulation went in behind the pipe rather than in front of it, that run is exposed to the cold face of the brick all winter. Ask what was done in the rehab before assuming the pipes are inboard.
Two units are affected. Does that change how the work is scoped and estimated?
It changes the access and it can change the repair, so it is worth flagging when you call. Cost varies by where the pipe turns out to be, how it is reached, how much of the run is replaced and how many units the work has to enter. Roto-Rooter provides on-site estimates before any work begins.
Contact Roto-Rooter to Trace the Leaking Pipe Before the Plaster Lets Go
Water inside a masonry wall does its damage out of sight, and the longer it sits the more of the wall has to come off to reach it. Roto-Rooter answers 24/7, 365 days a year and has been repairing pipes since 1935. Roto-Rooter is fully licensed and insured. Schedule online to get a technician out, or go straight to Chicago emergency plumbing while water is still running. If it reached framing, subfloor or insulation, Chicago water damage restoration takes over the drying once the pipe is closed, and Chicago plumbing is where the rest of the local work lives.