Utility connections are one of the most overlooked and underbudgeted aspects of ADU construction. They can account for 10-15% of your total project cost and, if poorly planned, can delay your project by months. This guide covers what you need to know.
Electrical Requirements
Electrical Panel
Most existing homes have 100-200 amp electrical panels. An ADU typically requires:
- Subpanel for ADU: 60-100 amps
- Main panel upgrade: Often needed if your existing panel is 100 amps or less
- Separate meter: Required in some jurisdictions; optional but beneficial for rental tracking
Electrical Costs
| Component | Cost Range |
|---|---|
| Panel upgrade (100A to 200A) | $2,000-$5,000 |
| Subpanel for ADU | $1,000-$2,500 |
| Trenching and wiring to ADU | $1,000-$3,000 |
| Separate meter installation | $500-$1,500 |
| Interior electrical (outlets, switches, lighting) | $3,000-$8,000 |
| Total electrical | $5,000-$15,000 |
Considerations
- Solar panel integration (30% federal tax credit available) can offset ADU electrical costs long-term
- Electric vehicle charging infrastructure adds $500-$2,000 but increases rental appeal
- Smart home wiring (Wi-Fi, smart thermostat, smart locks) adds $500-$2,000
Plumbing and Water
Water Supply
Options for ADU water supply:
- Tap into existing main: Most common; share the existing water meter ($1,000-$3,000)
- Separate water meter: Required by some utilities; costs $2,000-$8,000 including installation
- New water service: Rarely needed but very expensive ($5,000-$15,000+)
Hot Water
- Tankless water heater: Most efficient for ADUs; $1,500-$3,500 installed
- Small tank heater (30-40 gal): $800-$2,000 installed
- Heat pump water heater: Most energy-efficient; $2,000-$4,500 installed; may qualify for IRA rebates
- Shared with main house: Possible but not recommended (affects both units)
Plumbing Costs
| Component | Cost Range |
|---|---|
| Water line to ADU | $1,000-$4,000 |
| Drain/waste/vent piping | $2,000-$6,000 |
| Water heater | $800-$4,500 |
| Fixtures (kitchen, bath) | $2,000-$5,000 |
| Total plumbing | $6,000-$20,000 |
Sewer Connection
Sewer Options
Sewer is often the most complex and expensive utility connection:
- Connect to existing sewer lateral: Simplest option; run new drain line from ADU to existing sewer connection ($2,000-$6,000)
- New sewer lateral to main: Required if existing lateral is at capacity or too far ($5,000-$15,000)
- Septic system connection: For properties on septic, verify system capacity; may need system upgrade ($2,000-$10,000+)
Sewer Costs
| Component | Cost Range |
|---|---|
| Drain line to existing lateral | $2,000-$6,000 |
| New sewer lateral | $5,000-$15,000 |
| Sewer connection fee | $1,000-$5,000 |
| Septic system assessment/upgrade | $500-$10,000 |
| Total sewer | $2,000-$15,000 |
Sewer Considerations
- Video inspection of existing lateral recommended before construction ($200-$500)
- Some cities require sewer capacity studies for ADUs
- Grease interceptors may be required for the ADU kitchen
Gas Connection (If Applicable)
- Gas line extension: $1,000-$4,000 for trenching and piping to ADU
- Gas meter: Some utilities require a separate meter ($500-$2,000)
- All-electric option: Many new ADUs are going all-electric, eliminating gas entirely
- Cost savings: All-electric ADUs save $1,000-$4,000 on gas infrastructure
Total Utility Cost Summary
| Utility | Low Estimate | High Estimate |
|---|---|---|
| Electrical | $5,000 | $15,000 |
| Plumbing/water | $6,000 | $20,000 |
| Sewer | $2,000 | $15,000 |
| Gas (if applicable) | $1,000 | $4,000 |
| Total | $14,000 | $54,000 |
Typical range for most ADUs: $10,000-$30,000
How to Minimize Utility Costs
- Place ADU close to existing utilities — every additional foot of trenching adds cost
- Go all-electric — eliminates gas line costs and qualifies for IRA energy rebates
- Share water meter when allowed — saves $2,000-$8,000 vs separate meter
- Use existing sewer lateral — video inspect first, then connect if capacity allows
- Plan during design — coordinate utility routing with your architect to minimize trenching
Frequently Asked Questions
Can my ADU share utilities with the main house?
Many ADUs share water and sewer connections with the main house. Electrical typically requires a subpanel. Some jurisdictions require separate meters for rental ADUs. Check local requirements.
How long do utility connections take?
Utility companies must respond within 60 days in California (AB 2221). Actual installation takes 1-3 weeks. The biggest delays come from utility company scheduling. Apply for connections early in the project.
Do I need a separate electrical meter for my ADU?
Requirements vary by utility company and jurisdiction. Separate meters make billing easier for rental ADUs but add $500-$1,500 to the project. Some utilities require them; others leave it optional. Check with your local utility.
What if my sewer lateral is too small for an ADU?
If your existing sewer lateral cannot handle the additional flow, you will need a new or upgraded lateral. This can cost $5,000-$15,000 and may require street work permits. A video inspection before construction identifies this issue early.
Should my ADU be all-electric or include gas?
All-electric ADUs are increasingly popular due to lower installation costs, IRA energy rebates, and environmental benefits. Gas is becoming less common in new construction, and some California cities ban gas in new buildings. All-electric also simplifies utility connections and reduces ongoing costs.
Related Reading
- ADU Utility Hookups: Power, Water, Gas
- ADU Utility Connections: Shared vs Separate
- ADU Parking Requirements by State
- ADU Setback Requirements by State
- ADU Cost and Financing Guide 2026
-- The ADU Finder Team