Two ways to add square footage
A traditional home addition expands your main house (extra bedroom, larger kitchen, family room). An ADU adds an independent living unit with its own kitchen, bath, and entrance.
Cost comparison
| Project | Typical Cost (per sf) | Total for 500 sf |
|---|---|---|
| Home addition (mid-range) | Property-specific written estimate | Property-specific written estimate |
| Detached ADU | Property-specific written estimate | Property-specific written estimate |
| Attached ADU | Property-specific written estimate | Property-specific written estimate |
Relative pricing between an ADU and a home addition depends on site conditions, structural scope, utilities, permitting, and finishes; compare complete written estimates.
Rental income potential
- Home addition: Cannot be rented as a separate unit (no separate kitchen/entrance)
- ADU: Can be rented legally for $1,500–$4,000/month
For income properties, ADU wins decisively.
Property tax impact
Both ADU and addition trigger reassessment only on the new value added — not the entire property. California Prop 13 protections still apply.
Resale value
- Relative construction pricing depends on the site, scope, utilities, design, and finishes; request a property-specific written estimate.
- ADU: Recovers 90–115% of cost (and can be sold separately under AB 1033 in some cities)
Permitting difficulty
ADUs are explicitly favored by state law. Home additions follow standard residential zoning, which is often more restrictive.
When to choose home addition
- You want to upgrade your own family's living space
- You need a 4th or 5th bedroom for your kids
- You want a larger kitchen or great room
When to choose ADU
- You want rental income
- You need a separate caregiver suite
- You want maximum resale value
- You eventually want flexibility to sell separately
Frequently Asked Questions
Is an ADU cheaper than a home addition?
Per square foot, yes — typically 10–25% less.
Can a home addition be rented?
No — without a separate kitchen, bath, and exterior entrance, it is not legally a separate dwelling unit.
Which adds more value: ADU or addition?
ADU usually adds more total value because it generates rental income and can sometimes be sold separately.
Does an addition trigger property tax reassessment?
Only on the value added — not on the whole property under Prop 13.
Can I convert a home addition into an ADU later?
Yes — if you add a separate kitchen, bath, and exterior entrance, you can permit the conversion.
Related Vision ADU Resources
- ADU Property Tax Impact in California (2026 Reality Check)
- How to Build an ADU, Day 1: Architecture & Design
- How to Build an ADU, Day 2: Structural Engineering
- How to Build an ADU, Day 3: Title 24 Energy Compliance
- ADU Contractor in Los Angeles
- ADU Contractor in Glendale
- Los Angeles County ADU Builder
- Orange County ADU Builder
- Inland Empire ADU Builder
- 2026 ADU Cost Calculator
- All Vision ADU Service Areas