Utility Costs: Connections, Upgrades, and Trenches

Utilities are the budget category most controlled by your property rather than your choices. Same ADU, different lot, $40K swing. Here's where it goes.

Electrical ($3K–$20K+). The range depends on one question: does your main panel have capacity? A modern 200-amp panel often serves both dwellings with a subpanel to the ADU ($3K–$6K including the trench). An old 100-amp panel usually means a service upgrade ($5K–$15K+, and utility timelines apply). A separate new meter costs more still — Module 7 covers when it's worth it.

Sewer ($4K–$20K+). Your ADU's waste has to reach a sewer line. Short gravity run to an accessible lateral: cheap end. Long run, deep connection, or — the budget-eater — an ADU below the sewer line requiring a sewage ejector pump: expensive end. On septic? Different conversation entirely, and worth having early.

Water ($1K–$8K). Usually the easy one: tee off the existing service. It gets pricey only when the existing service is undersized for two dwellings or when the meter itself needs upsizing.

Trenching (woven through all of it). Every utility travels in a trench, and trenches cost by the foot — more through concrete, roots, rock, or anything that must be demolished and restored. This is why an ADU placed near existing utilities can save $10K–$20K versus the identical unit at the far corner of the lot. Placement is a budgeting decision, not just a design one.

Gas (optional, increasingly skipped). Extending a gas line costs $2K–$8K; many new ADUs go all-electric and skip it entirely — often required or incentivized anyway (Module 7).