An accessory dwelling unit, whether a backyard cottage or a garage apartment, adds a second kitchen and bathroom to a lot that was plumbed for one house. The new unit drains either into the existing lateral or to a new tap at the street, and the existing lateral almost always runs through the yard where the ADU will be built. The camera inspection answers the two questions the site plan depends on: where exactly is the lateral, and can it take the load.
Quick answer: before designing an ADU, camera the lateral from the house cleanout to the main and locate it with the sonde across the yard, marking route and depth; confirm its material, condition and diameter; identify a connection point with enough fall from the ADU’s fixtures; and check with the utility whether a second unit may share the lateral or needs its own tap. Repair or replace a failing lateral before the ADU is built over or beside it. Record the baseline.
Where the lateral runs
The lateral crosses the yard from the house to the street, and the ADU is going into that yard. A building over the lateral is a repair problem forever; a footing beside it may be within the trench of any future excavation. The camera and sonde draw the lateral on the ground with depths, and the site plan is then drawn around it, with the setbacks the local code requires from a sewer. See locating the head underground and inspection before landscaping.
Material and condition
A lateral old enough to serve a house that now has room for an ADU is likely clay, cast iron, Orangeburg or early plastic. The camera establishes which, and whether it is sound. A clay lateral with roots at every joint, or Orangeburg that is deforming, should be replaced before a second dwelling depends on it, and the replacement is far cheaper before the ADU is built. Clay pipe priorities and Orangeburg expectations cover the materials.
Diameter and capacity
Most residential laterals are 4 in, and a 4 in lateral in good condition serves two dwellings in most codes. The camera confirms the diameter, which can be read from the picture with a known-size reference or from the footage of fittings, and confirms that the bore is not reduced by scale or a partial collapse. A lateral that is already running at the edge of its capacity because of a belly or heavy scale is not a candidate for a second kitchen. Sewer capacity for additions goes further.
The connection point
The ADU’s drain has to join the lateral downstream of the house’s connection with fall from the ADU’s fixtures to the joint. The sonde depth at candidate points along the route tells the designer whether gravity works or an ejector is needed. A connection into a sound section of pipe, away from existing joints and defects, is chosen from the footage. Where the lateral is being replaced anyway, the new wye for the ADU goes in with it.
Shared lateral or new tap
Utilities differ on whether an ADU may share the main house’s lateral or must have its own connection to the main. A new tap is expensive and involves the street; a shared lateral puts two households on one pipe and one cleanout. Ask early, and bring the footage: a utility that sees a sound 4 in lateral is more likely to allow sharing than one that is asked blind.
Cleanouts
A shared lateral needs a cleanout downstream of the ADU connection and the existing one upstream, so that each section can be inspected and cleared separately when there is a blockage and a dispute about whose it is. Specify them in the plans.
Construction protection
Once the lateral is marked, the builder needs its route and depth in writing, plating where equipment will cross it and hand digging at any footing near it. A lateral crushed by a concrete truck during ADU construction is a common and expensive story. See calling 811 before digging.
After construction
Camera the lateral again from the house cleanout through the new connection to the main, and camera the ADU’s own drain from its cleanout to the joint. The footage confirms the connection, the slope and that nothing from the construction is in the pipe. Keep it with the permit.
What to record
The route and depths across the yard, photographed against the site plan. Material, diameter and condition with distances. The chosen connection point and its depth. The utility’s answer on sharing. The after footage. An ADU is often built to be rented or sold, and the next owner will want to see all of it.
Ejector or gravity for the ADU
A garage apartment above grade drains by gravity to almost any lateral depth. A backyard cottage at grade, or a unit with a basement bathroom, depends on the lateral being deep enough at the connection point for the required fall. If it is not, the ADU needs its own ejector pit and pump, which is a cost, a maintenance item and a point of failure that should appear in the budget before the design is finished rather than after the slab is poured. The sonde depth reading at the chosen connection point is what decides it, and it is worth taking two or three readings along the route to find the deepest convenient tie-in.
Common questions
Can an ADU share the house’s sewer lateral?
Often, if the lateral is 4 in and sound and the utility permits it. Some require a separate tap. Ask before designing.
How do I find the lateral in my yard?
A camera with a sonde, located from above with a receiver, paints the route and estimates depth. Utility records are usually approximate.
What if the lateral is failing?
Replace it before building. A new lateral with a wye for the ADU is far cheaper than repairing an old one under a new building later.
Related guides
See building lateral push camera basics, measuring lateral length, and serviceability questions to ask.