TL;DR
Placeholder summary. An attached ADU shares at least one wall with the main house, cutting foundation and utility hookup costs compared to a fully detached structure while still giving occupants a separate entrance.
Cost: $95,000 to $200,000Size: 400 to 800 sq ftTimeline: 5 to 10 monthsPermit complexity: Moderate
Last verified: July 15, 2026
Placeholder content. Real attached ADU content will replace this in the next phase.
How Attached ADU compares to the alternatives
Cost, size, timeline, and permit difficulty for all five ADU types side by side, with Attached 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 ADUYou are here | Garage Conversion | Junior ADU | 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.