Connecting an ADU or Tiny House to your existing sewer?

A frustrated potential customer calls because she’s having trouble getting a permit from the local city, for an ADU (accessory dwelling unit) Sound familiar?

In most cities in the Puget Sound region, you can tap into your homes existing sewer connection to the city sewer main for your mother in law or ADU structure built on the same lot.

In this case, original home was built in the thirties or so. It’s connected to the city sewer system and they want to connect the apartment over the garage (fully permitted, but never occupied) to the sewer. The city wants a bunch of information on a site plan with elevations, including existing underground sewer pipe. Without a site plan with correct information-no permit. Without digging up the existing sewer pipe, this information could be impossible to get.

Typically, we would use a Google overhead image as a basis for the site plan, as its cheap and easy. Showing the building locations, streets sidewalks, etc. is easy from overhead photos.

As far as determining elevations for the sewer—we would choose one of our high-quality sewer cameras equipped with a transmitter. We can push the camera anywhere in the pipe and pinpoint locate it, including depth and orientation.

Modern camera transmitters are very accurate, but must be operated by a trained professional in order to get accurate and reliable results. That information, along with measurements from existing permanent structures, can be used to map the location of existing buried pipe and determine the direction of flow and the amount of fall any pipe might have. Generally, a 2% slope will be a minimum requirement, although exceptions might be made, by variance or agreement of some kind. If minimum slope cannot be obtained, a sewage ejection pump will need to be installed. By using this information, we can determine where we might intersect the existing pipe and what depth the pipe needs to exit the new structure. We may make route adjustments to avoid other structures or landscaping by using this information to plan the route of the new pipe. This information can now be added to our site plan to be submitted for approval. We have not disturbed any soil and saved our customers a lot of money in the process.

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