TL;DR
Placeholder summary. A junior ADU is carved out of the existing footprint of the main house, typically a bedroom with an added kitchenette, making it the cheapest and fastest ADU type to build.
Cost: $20,000 to $100,000Size: 150 to 500 sq ftTimeline: 2 to 5 monthsPermit complexity: Low
Last verified: July 15, 2026
Placeholder content. Real junior ADU content will replace this in the next phase.
How Junior ADU compares to the alternatives
Cost, size, timeline, and permit difficulty for all five ADU types side by side, with Junior ADU highlighted. The right pick usually comes down to how much lot space and budget you actually have, not which one you like best.
| Feature | Detached ADU | Attached ADU | Garage Conversion | Junior ADUYou are here | Above-Garage ADU |
|---|---|---|---|---|---|
| Typical cost | $120,000 to $360,000 | $95,000 to $200,000 | $55,000 to $140,000 | $20,000 to $100,000 | $100,000 to $280,000 |
| Typical size | 400 to 1,200 sq ft | 400 to 800 sq ft | 300 to 650 sq ft | 150 to 500 sq ft | 400 to 800 sq ft |
| Typical timeline | 6 to 12 months | 5 to 10 months | 3 to 6 months | 2 to 5 months | 7 to 12 months |
| Permit complexity | Moderate | Moderate | Low | Low | High |
| Best for | Owners who want maximum privacy and a fully independent living space | Owners who want an ADU without giving up backyard space | Owners on a budget who already have an underused garage | Owners who want rental income fast at the lowest possible cost | Owners with a detached garage and little extra lot space to build on |
Other ADU types
See how the rest of your options stack up.