What ADUs cost in Southern California
As a rough anchor, ground-up ADU construction in our service area generally runs $285–$350 per square foot, though your exact number depends on the ADU type, finish level, site conditions, and the contractor you choose. Converting existing space — a garage or an interior room — usually costs less per project because you reuse structure. Here's how the main types compare on total cost:
| Type | Typical construction cost | Est. rent | Value added |
|---|---|---|---|
| Detached ADU | $170K–$420K+ | $1.8K–$2.8K/mo | $160K–$320K+ |
| Attached ADU | $140K–$280K | $1.6K–$2.2K/mo | $120K–$220K |
| Garage Conversion | $115K–$210K | $1.3K–$1.9K/mo | $90K–$170K |
| Junior ADU (JADU) | $70K–$140K | $1.1K–$1.7K/mo | $50K–$90K |
These are general market estimates for planning purposes only — not quotes, appraisals, or guarantees. Actual figures depend on your property, market conditions, and financing. A licensed contractor, appraiser, or lender can give you numbers specific to your project.
What actually drives the price
The return side: value, rent, and equity
Why homeowners build
Added property value. A well-built ADU can add meaningful resale value — see whether an ADU increases property value.
Rental income. A long-term income stream for as long as you own the property — see the rental income guide and the ROI calculator.
Access to equity. Once construction is complete, some homeowners tap the equity they've built through refinancing.
These are general patterns, not guarantees — actual value, financing terms, and rental income depend on your property, market, and lender.
How homeowners pay for it
Most ADU projects are funded through a HELOC, a cash-out refinance, a construction loan, or a combination. Each works differently; our ADU financing overview compares them, the HELOC vs. construction loan and cash-out vs. HELOC guides go deeper, and the loan payment calculator estimates a monthly payment. If you plan to rent, lenders may count projected rental income toward qualification.
Estimate your project
ADU cost questions, answered
As a rough anchor, ground-up construction generally runs $285–$350 per square foot in our service area. In total, that tends to land around $70K–$140K for a Junior ADU, $115K–$210K for a garage conversion, and $170K–$420K+ for a detached unit. These are planning estimates only — your number depends on the type, finish level, site conditions, and contractor. A licensed contractor can give you a real quote.
On a new detached unit, the foundation, framing, and the kitchen and bathroom usually carry the most cost, followed by utility connections. Beyond the build itself, soft costs — design, permits, and impact fees — add up and are easy to overlook when you're comparing bids.
Yes — converting existing space costs less than building new because you reuse structure. A Junior ADU (an interior conversion) and a garage conversion are typically the lowest-cost paths, while a new detached unit sits at the top of the range. Our conversion vs. detached guide compares the trade-offs.
Most projects are funded through a HELOC, a cash-out refinance, a construction loan, or some combination — occasionally cash. Each works differently, and terms depend entirely on your lender and finances. Our financing overview compares the options and the loan calculator estimates a monthly payment.
Generally, only the ADU's added value is assessed — in California your existing home typically isn't reassessed just because you add a unit. So the increase applies to the new construction, not your whole property. The exact impact varies by county; our property-tax estimator gives a rough figure, and your county assessor confirms it.