ADU sewer connections in Sacramento: what sets the cost

The basic problem

An ADU's drains have to reach the sewer, usually by tying into the existing lateral from the main house. Sewage flows by gravity, so the pipe needs steady downhill slope all the way. The farther the ADU sits from the main lateral, and the flatter the lot, the harder that becomes.

Flat lots and slope

Much of the Sacramento Valley floor is very flat. A rear ADU on a deep lot may sit too low relative to the existing lateral to drain by gravity, especially if the main sewer is shallow. When that happens, a sewer ejector pump lifts the waste to the connection.

Check the existing lateral first

Before design is final, the existing sewer lateral should be inspected with a camera. Older clay or Orangeburg laterals with roots or cracks may need repair or replacement before a second dwelling ties in.

Finding that early lets the repair be part of the plan instead of a surprise after the slab is poured.

Water and gas

The ADU also needs water and, if you choose, gas. Many owners run a new water line from the main house; some choose a separate meter. Going all-electric with a heat pump water heater removes the gas line from the plan entirely.

Garage conversions are different

Converting an attached or detached garage often puts the new bathroom close to the main house, which shortens the sewer run. The catch is the slab: drains for a toilet, shower and sink have to be cut into existing concrete and sloped to the connection. Planning the bathroom near the side of the garage closest to the existing lateral keeps that trenching short.

Questions to settle before you build

How deep is the existing sewer at the house? How far is the ADU from it? Is gravity possible, or will a pump be needed? What condition is the lateral in? Answering these first keeps the ADU plumbing budget honest.

Questions readers ask