Do I need a separate water service line for my accessory structure?

Missoula’s rules allow a primary residence and one accessory structure (ADU, garage, workshop, etc.) to share a water service line, but only if there is adequate capacity as determined by the Uniform Plumbing Code (UPC). UPC requires a fixture count to be completed for all fixtures that will receive water from the shared service line (i.e. including the existing primary structure and the accessory structure). Most existing water service lines in Missoula are ¾” galvanized pipes and very rarely (if ever) will a ¾” line meet the total fixture count demand of a house plus an accessory structure. In addition, many existing galvanized service lines are already beyond their expected useful life and should be evaluated for replacement. Anyone planning to build an accessory structure on a property with only a single ¾” service line should plan to replace the service with a modern 1-inch polyethylene (PE) service. 

Note that two primary residences on a single parcel will always be required to have separate services. Any future subdivision or townhome creation will also require separate services for each lot or townhome.

Show All Answers

1. Do ADUs require additional parking?
2. Are there design standards for ADUs?
3. Can I convert my garage to an ADU?
4. Is it required that the homeowner live in the primary residence?
5. I have been notified of my neighbor’s intent to build an ADU. Is there anything I can do to prevent it from being built?
6. I would like to build an ADU, where should I begin?
7. Can an ADU share utility infrastructure with a primary residence?
8. What if I have an existing second dwelling unit not approved through a permit process?
9. Who owns the water and sewer services lines?
10. Do I need a separate water service line for my accessory structure?
11. If my existing house is billed for water as a flat rate, can I add an accessory building to the account?
12. Do I need a separate sewer service line for my accessory structure?
13. Where do I find information about my existing water or sewer service line?
14. How do I complete a fixture count?
15. Do I need a separate water meter for my accessory structure?
16. Can my accessory structure be billed separately for water?