Side-By-Side Comparison
| Factor | ADU | Garage Conversion |
|---|---|---|
| Typical cost | $150,000 to $400,000+ | $75,000 to $220,000+ |
| Timeline | 4 to 10+ months depending on permits and utility scope | 2 to 5 months when structure is usable |
| Best for | Rental income, family suite, long-term property value | Faster extra living space, office, studio, or smaller rental plan |
| Main risk | Utility upgrades, setbacks, plan review, site constraints | Parking replacement, ceiling heights, waterproofing, existing slab condition |
Contractor Recommendation
If the garage structure is sound and the property can satisfy parking and code requirements, a garage conversion is usually the faster value play. If the goal is maximum rental income, privacy, or long-term resale impact, a detached ADU is often the stronger investment even though the upfront cost is higher.
Do not choose from averages alone. Start with the property constraints: access, utility route, setbacks, parking, drainage, and whether the existing garage shell is worth saving.