What Are the ADU Utility Hookup Requirements?
ADUs need water, sewer or septic, and electrical service sized for the added load. Many jurisdictions allow shared connections with the primary home, while some require separate meters. Utility capacity letters are often part of the permit package, and hookup or impact fees vary widely.
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Water and sewer
The water service and sewer lateral must handle the ADU's additional demand, and undersized lines may need upsizing. Many cities allow the ADU to share the existing connection; others require separate laterals or meters. Capacity and impact fees for water and sewer are the most variable cost in ADU development, ranging from modest to five figures depending on the utility.
Electrical service
The existing electrical panel must have capacity for the ADU's loads, or the service gets upgraded. Separate meters give clean billing for rentals but add meter and trenching costs; submeters or shared service are cheaper but complicate tenant billing. All-electric ADUs are increasingly common and simplify the utility picture.
Getting will-serve letters early
Water and sewer providers issue will-serve or capacity letters confirming they can serve the ADU, and building departments often require them before issuing permits. Septic properties go through the health department instead. These letters occasionally reveal capacity moratoriums or expensive main extensions, which is exactly why you get them during feasibility.
The bottom line
Utility capacity and fees can make or break ADU feasibility. Get will-serve letters before you finalize the design.