The Plumbing Phase: Making Your ADU Livable
Plumbing is what transforms a structure into a livable space. Without it, you have a fancy shed. With it, you have a kitchen, bathroom, and laundry — everything needed for independent living.
Major Plumbing Systems
Water Supply
Fresh water is brought to your ADU from your property's main water line. This involves:
- Tapping into the existing water main (or installing a new connection)
- Running supply lines (typically PEX or copper) to all fixtures
- Installing shut-off valves at the water heater and each fixture
- Ensuring adequate water pressure (typically 40-80 PSI)
Drain/Waste/Vent (DWV)
Wastewater must be carried away from every fixture to the sewer or septic system:
- Drain lines from sinks, showers, toilets, and appliances
- Vent pipes that extend through the roof to allow proper drainage
- Cleanout access points for future maintenance
- Connection to the main sewer line (this often requires a city inspection)
Gas Lines (if applicable)
If your ADU uses gas appliances (stove, dryer, water heater):
- Gas supply line from the meter to the ADU
- Individual gas lines to each appliance
- Proper sizing to ensure adequate gas flow
- Gas pressure testing before activation
Plumbing Rough-In vs. Finish
Rough-In (During Framing)
All pipes are installed inside walls and under floors before drywall:
- Supply lines to every fixture location
- Drain lines with proper slope (1/4" per foot minimum)
- Vent lines routed through walls to the roof
- Water heater connections
- Washing machine connections
Finish (After Drywall & Painting)
Fixtures are installed near the end of the project:
- Toilets, sinks, faucets
- Shower/tub fixtures and heads
- Garbage disposal and dishwasher connections
- Water heater commissioning
Water Heater Options
Heat Pump Water Heater (Recommended)
- Most energy-efficient option
- Required by Title 24 in many cases
- Higher upfront cost but lower operating costs
- Needs adequate space for air circulation
Tankless Water Heater
- Provides hot water on demand
- Space-saving (wall-mounted)
- Gas or electric options
- Good for small ADUs with lower hot water demand
Budget
Plumbing for an ADU requires a property-specific written estimate, with sewer connection being the most variable cost factor.
Coming Up Next
Day 10: Insulation & Drywall — sealing your ADU for comfort and finishing the interior walls. The space starts to feel like a real home.
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Vision ADU's licensed plumbers handle every aspect of ADU plumbing. Get started with a free estimate.
Related Vision ADU Resources
- How to Build an ADU, Day 11: HVAC — Heating & Cooling
- How to Build an ADU, Day 12: Roofing
- How to Build an ADU, Day 13: Bathroom Tile & Shower
- How to Build an ADU, Day 14: Flooring
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