After 30 years of building ADUs across Santa Cruz and Monterey Counties, the question I get asked more than any other is simple: how much is this going to cost me?
The honest answer is — it depends. But "it depends" isn't helpful when you're trying to decide whether to move forward. So in this guide, I'm going to give you real numbers, real ranges, and the factors that push costs up or down on the Central Coast.
Starting price for a garage conversion ADU
All-in cost for a full detached 2BR ADU
Typical timeline from permit to move-in
Not all ADUs are created equal. Here's a breakdown of what you can realistically expect to pay for each type:
| ADU Type | All-In Cost Range | Best For |
|---|---|---|
| Garage Conversion | $135,000 – $175,000 | Existing garage, lowest entry cost |
| Junior ADU (JADU) | $80,000 – $140,000 | Interior conversion of existing space |
| Attached ADU | $160,000 – $230,000 | Addition to existing home |
| Detached ADU (1BR) | $180,000 – $250,000 | Maximum rental income, standalone unit |
| Detached ADU (2BR) | $220,000 – $300,000 | Highest rental income potential |
| Two-Story ADU | $250,000 – $320,000 | Maximum square footage on small lots |
When Peninsula Construction quotes an ADU, our all-in pricing includes everything from the first shovel to the final inspection. Here's what's covered:
💡 Peninsula Advantage: We include a property evaluation and after-build value assessment with every estimate, plus financing options up to $100,000. Most contractors won't do this — we do because we want you to understand the full financial picture before you commit.
Santa Cruz County has some of the highest construction costs in California. Here are the main factors:
The most accurate ADU cost comes from a site visit. Every property is different — lot size, soil conditions, utility locations, existing structures, and HOA rules all affect pricing. At Peninsula Construction, our initial consultation is free and includes a property walkthrough and preliminary budget range.
We also offer three design options for 2-bedroom ADUs under 750 square feet, so you can choose the layout that fits your goals and your budget before construction begins.
In most cases on the Central Coast — yes, absolutely. Rental rates in Santa Cruz and Monterey Counties are among the highest in the country. A well-built 1-bedroom ADU can rent for $2,200–$3,000 per month. At those rates, a $200,000 ADU pays for itself in 6–8 years — and adds significant value to your property the moment it's permitted.
Ready to find out exactly what your ADU would cost?
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