Module 7 · Lesson 1
ADU Utilities Explained
Every ADU needs power, water, and sewer — and each involves one big decision. The homeowner's map to ADU utilities in plain English.
Utilities are the least glamorous part of ADU planning and the source of the most mid-project surprises. This module exists because a $30K utility surprise hurts more than any tile choice ever will. Let's build the map.
Every ADU needs three connections — and each has one central question:
Power. The question: does your existing electrical service have room for a second home? Your ADU's electricity comes either through your existing panel (shared or via subpanel) or through its own new meter. Which path — and whether your panel needs an upgrade first — is lessons 7.2 and 7.3.
Water. The question: can the existing service feed two homes? Usually yes — a tee off your existing line with a shutoff valve. Occasionally the service or meter needs upsizing. The easy utility, most of the time (lesson 7.5).
Sewer. The question: can waste flow downhill to the sewer? Gravity is free and pumps are not. Your lot's slope and the sewer's location decide which one you're buying (lesson 7.4).
Gas is now optional. Many ADUs skip gas entirely — all-electric design with heat-pump appliances is cheaper to connect, increasingly favored by code, and simpler forever (lesson 7.6).
Why utilities deserve a whole module: they're decided by things you can't see (pipe locations, panel capacity, line depths) and they're brutally location-dependent — which is why lesson 7.10 shows how utility locations sometimes redesign the whole project. The rule for everything ahead: find out what exists before designing what's new.
Key takeaways
- Three required connections — power, water, sewer — each with one central question.
- Power: does the panel have capacity? Water: can the service feed two homes? Sewer: will gravity work?
- Gas is optional, and all-electric ADUs skip it entirely.
- Investigate what exists before designing what's new — utility surprises are the expensive kind.