Decision Guide · San Francisco
By Solid Bay Construction SF | Updated 2026
Both a Junior ADU and a full ADU let you add housing on your existing lot — but they're built differently, cost differently, and serve different goals. Here's how to tell which one fits what you're trying to do.
| Junior ADU (JADU) | Full ADU | |
|---|---|---|
| Max size | 500 sq ft | No fixed cap; typically 800–1,200 sq ft |
| Kitchen | Kitchenette (efficiency kitchen) only | Full kitchen required |
| Bathroom | Can share with main house, or have its own | Must have its own |
| Location | Must be within the existing structure of the home | Can be within, attached, or fully detached |
| Typical cost | $80,000–$180,000 | $180,000–$550,000+ depending on type |
| Best for | Lower-cost path to a rentable or family space within your existing footprint | Maximum rental income or a fully independent living situation |
A JADU is the lower-cost, lower-disruption option because it's built within your home's existing walls — converting an existing room or basement area rather than adding new structure. It's a strong fit if you want a modest income unit or space for a family member without the cost of a full separate unit, and you're comfortable sharing a bathroom or building a small one within the existing footprint.
If your goal is maximum rental income, a fully independent unit for long-term tenants, or a garage conversion that becomes a genuine separate home, a full ADU is the right category. It costs more, but a complete kitchen, private bathroom, and separate entrance make it far more marketable as a long-term rental.
Yes — under current California law, most San Francisco single-family properties can build one ADU and one JADU on the same lot, both by right without a discretionary hearing. This is an increasingly common approach for homeowners who want both a rental unit and a smaller space for family, built in a single permitting and construction process.
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