Chicago's combined sewers push water back into basements during heavy rain. Here's how landlords and property managers inspect backwater valves, maintain floor drains, and keep garden units dry through fall storm season.
Most owners picture basement flooding as water coming through a crack in the foundation wall. In a lot of Chicago buildings, that is not what happens. The water comes up through the floor drain.
Much of Chicago sits on a combined sewer system, meaning street stormwater and building wastewater share the same pipe. That works fine most of the year. During a heavy summer or fall downpour, the mains fill faster than the Deep Tunnel and reservoir system can draw them down, and the sewer in the street can briefly sit higher than the lowest drain in your building.
Gravity then does what you would expect. The lowest opening becomes the relief point, and that is almost always a basement floor drain, a laundry standpipe, or a garden unit shower. Owners in Albany Park, Logan Square, and Portage Park see this repeatedly, and it has nothing to do with how well the foundation is sealed.
A backwater valve, sometimes called a backflow preventer or check valve, sits in the building's main sewer line. Normally a flap inside hangs open and lets waste flow out to the street. When flow reverses, pressure pushes that flap closed and seals the line, so the surcharged main cannot come back into the building.
It is a simple mechanical device with no power supply, which is both its strength and its weakness. Nothing fails electrically, but nothing tells you when it stops working either. A flap held partly open by a wipe, a rag, a root, or years of grease looks normal until the night you need it.
One detail owners miss: while the valve is closed during a storm, the building cannot discharge either. Tenants running showers or laundry in that window are sending water into a sealed line with nowhere to go.
Plenty of owners inherit a building and never learn what is under the basement slab. Start with a visual check. A backwater valve is usually accessed through a cover set flush in the basement floor, near where the main line heads toward the street and within a few feet of the front foundation wall.
If you find a cleanout cap but no access cover, you may only have a cleanout, which offers no protection. In many vintage greystones and two-flats in Wicker Park, Ravenswood, and Humboldt Park, the original construction included neither, and any valve present was retrofitted later.
If the visual check is inconclusive, a licensed plumber can run a sewer camera from the cleanout and tell you in twenty minutes what you have and what shape it is in. Backflow prevention requirements vary by situation and municipality, so confirm current rules with a plumber before planning an installation.
Contact Lena Services INC at 773-939-4284 or [email protected]