Understanding Your Factory-Built Options
Not all factory-built homes are created equal. While the terms "prefab," "modular," and "container" are often used interchangeably, they represent distinctly different products with different costs, quality levels, and livability outcomes. Here's what California homeowners need to know.
Prefab ADU: Purpose-Built for Living
Prefab ADUs are designed and manufactured specifically as residential units. Companies like EVO ADU engineer every detail — from the steel frame to the interior finishes — for comfort, durability, and compliance with California building codes. Prefab ADUs arrive largely complete and are installed on a prepared foundation.
- Cost: $135,000 - $250,000
- Timeline: 3-5 months total
- Quality: High — factory-controlled precision
- Customization: Moderate — choose from model options and finishes
- Resale value: High — looks and functions like a traditional home
Container ADU: Recycled but Compromised
Shipping container ADUs repurpose steel shipping containers into living spaces. While the concept sounds sustainable and affordable, the reality is more complex. Containers require extensive modification to meet residential building codes, and their narrow 8-foot width creates awkward living layouts.
- Cost: $100,000 - $200,000 (after modifications)
- Timeline: 4-8 months
- Quality: Variable — depends heavily on conversion quality
- Customization: Limited by container dimensions (8'x20' or 8'x40')
- Resale value: Low to moderate — stigma of "container living"
Modular Home: Larger but Different Classification
Modular homes are factory-built in sections and assembled on-site. They're typically larger than ADUs (1,000+ sq ft) and may be subject to different building codes. True modular homes built to local building codes (not HUD code) are high-quality but designed for primary residence use.
- Cost: $200,000 - $400,000+
- Timeline: 6-12 months
- Quality: High — if built to local building code (not HUD code)
- Customization: High — many floor plan options
- Resale value: High — equivalent to site-built
Head-to-Head Comparison
| Factor | Prefab ADU | Container ADU | Modular Home |
|---|---|---|---|
| Starting price | $135K | $100K | $200K |
| Move-in ready | 3-5 mo | 4-8 mo | 6-12 mo |
| Fire resistant | Yes (steel) | Partial | Varies |
| CA ADU compliant | Yes | Varies | May exceed size |
| Livability | Excellent | Limited | Excellent |
| Rental appeal | High | Low-Med | High |
The Verdict
For most California homeowners looking to add a backyard unit, a purpose-built prefab ADU offers the best balance of cost, quality, timeline, and livability. Container ADUs may seem cheaper but often cost nearly as much after required modifications, while delivering a less comfortable living experience. Modular homes are excellent but are typically overkill for an ADU project and may exceed size limits.