A house with a basement has fixtures and floor drains below the level of the street, which makes the basement the place where every sewer backup, whether from the house’s own lateral or from a surcharged main, arrives first. It also gives direct access to the building drain’s cleanout and the stack bases, which makes inspection easier than in a slab house. A buyer of a basement home should use that access to answer one question: has this basement flooded from the sewer, and will it.
Quick answer: in a basement house, camera the main line from the basement cleanout to the street, inspect every floor drain and its trap and branch, look at the stack bases, check whether a sump or footing drain is connected to the sanitary sewer, look for the evidence of past backups, and establish whether a backwater valve is present and working. Weight any main-line finding by the fact that the basement is where its consequences land.
Evidence of past backups
Before any camera, look. Tide marks on walls and posts, replaced lower drywall, new flooring in an old basement, rust lines on appliance feet, a smell, and a floor drain with a fresh cover or a plug in it. Ask the seller directly and read the disclosure. Disclosure obligations cover backups specifically.
The main cleanout
Most basement houses have a cleanout on the building drain near where it exits the foundation, often a cast iron plug in the floor or a stack. Find it, confirm the plug comes out, and camera from it toward the street. This is the inspection that covers the lateral. Cleanout access covers finding and opening it.
Floor drains
Each floor drain is a trap, a branch and a connection to the building drain, and each is a path for a backup into the room. Pull the grate, check the trap holds water, camera the branch to the main. A floor drain that has been plugged is a sign of past backups; one with a backwater device in it is a sign someone tried to stop them. Inspecting a floor drain covers the method and the picture of a floor drain backup what it shows.
Stack bases
Cast iron stacks rust through at the base in the basement. Look for scale and weeping where each stack meets the floor or the drain, and camera into the base from the cleanout if there is one. A failing stack base is a repair now.
Sump and footing drains
A sump pump should discharge outside or to a storm sewer, never to the sanitary sewer; footing drains likewise. A sump tied into the sanitary line overloads the sewer in rain and pushes the sewer back into the basement when the main is full. The camera from the main cleanout shows every connection; a sump discharge entering it is a finding.
The main under the slab
The building drain runs under the basement floor from the stacks to the exit. Camera it, locate it with the sonde and note the depth, because a repair under a basement slab is a floor repair. Bellies from settlement, channeled cast iron and offsets at the foundation wall are the usual findings. Repair under a slab covers the cost.
The lateral and the main
Camera to the street and look at the tap. If the main is seen running full on a dry day, or the street floods in storms, the basement is exposed to surcharge regardless of the lateral’s condition, and the question becomes backwater protection. Inspecting a full line covers reading a surcharged main.
Backwater valve
Check whether one is installed, where, and whether its cover is accessible and its flap moves. A basement house in a surcharge-prone area without one is a flood waiting for the right storm, and installing one is a floor-cutting job. Inspection before a backwater valve covers the install.
Finished basements
A finished basement hides the cleanouts, the stack bases and the evidence, and multiplies the cost of a backup. Insist on access to the cleanout and camera it anyway; if the cleanout has been drywalled over, that is a finding. See inspection before finishing a basement for what should have been done.
Insurance
Standard policies often exclude sewer backup. A basement house with any history or any surcharge risk needs the rider, and the camera report is what shows the insurer the line’s condition.
What to record
The evidence of past backups photographed. Footage from the cleanout to the main with distances and the main’s condition at the tap. Each floor drain’s condition. Stack bases. Sump connections. Backwater valve presence and condition. Depth of the drain under the slab. This is the basement’s drainage file.
Reading the floor drain itself
A floor drain tells its own story before any camera. A grate rusted in place has not been lifted in years; a trap with no water in it is dry and letting sewer gas into the room; a trap primer line or a trickle from a nearby fixture means someone has dealt with that problem; a rubber plug, a standpipe or a screw-down backwater insert in the drain means someone has dealt with backups. Each of those is a question for the seller and a note for the file.
Common questions
Why do basements flood from the sewer?
Because their fixtures and floor drains are below the street. A blocked lateral or a full main sends sewage to the lowest opening, and that is the basement.
Can a camera tell if a basement has backed up before?
Not directly. The room shows the evidence; the camera shows the cause.
Should every basement house have a backwater valve?
Every one in an area where the main surcharges, and every one with a finished basement, should at least consider it.
Related guides
See inspection after a basement flood, cameras for basement drains, and slab foundation homes.