Costs
What an ADU actually costs in Los Gatos in 2026
Most ADU prices you see online are per square foot, construction only. That number leaves out about a third of what you will actually write checks for. Here is the full list, from our own detached ADU projects in Los Gatos, Monte Sereno and Saratoga over the last two years.
| Line item | Typical range |
|---|---|
| Design and engineering | $35k to $55k |
| Permits and plan check | $8k to $15k |
| School and impact fees | $0 to $12k |
| Sewer, water and electric connections | $15k to $45k |
| Site work and foundation | $30k to $70k |
| Construction | $190k to $255k |
| All in | $280k to $450k |
No real project hits every low number or every high one, so the total is a range of real jobs, not the sum of the columns.
Design and engineering
Architecture, structural engineering, a Title 24 energy report and, on sloped lots, a soils report. A simple studio on a flat lot sits at the low end. A two bedroom on a hillside with a retaining wall sits at the top.
Fees, the part people forget
Under 750 sq ft, impact fees are waived. School fees kick in above 500 sq ft and are charged per square foot. That is why so many ADUs in town are 499 or 749 sq ft. That is deliberate, and it can be the right call.
Utilities are the wild card
If the ADU sits near the main house and the sewer runs downhill to the street, connections are cheap. If it sits at the back of a lot that slopes away from the street, you may need a sewage ejector pump and a new electrical panel. That is the $45k end of the range. We find out on the site walk, before you pay for drawings.
Construction
The biggest line and the most predictable one. Framing, roofing, windows, systems, kitchen, bath and finishes. Our numbers include a real kitchen with full-size appliances, because the ADU you rent out or move a parent into needs one.
How to keep it at the low end
- Keep it close to the main house and the existing utilities.
- Pick a flat part of the lot, even if the view is better on the slope.
- Stay under 750 sq ft if the plan works at that size.
- Use one simple roof form. Every extra corner costs money.
Want to know where your lot lands in this table? That is the whole point of the free site walk. Book a site walk or read more about how we design and build ADUs.