Prefab vs Stick-Built ADU
Factory-built (prefab) ADUs have exploded in popularity, promising faster timelines and predictable pricing. But traditional site-built (stick-built) construction offers flexibility that prefab can't match. Here's how to choose.
Quick Summary
Prefab cost
$150K-$250K
Stick-built cost
$150K-$350K+
Decision factors
Site access, timeline
Head-to-Head Comparison
| Factor | Prefab | Stick-Built |
|---|---|---|
| Timeline | 3-6 months total | 6-12 months typical |
| Cost range | $150K-250K (fixed) | $150K-350K+ (variable) |
| Customization | Limited options | Unlimited flexibility |
| Pricing certainty | Fixed price typical | Cost overruns common |
| Site access needed | Crane access required | Minimal requirements |
| Quality control | Factory controlled | Varies by contractor |
| Site disruption | Minimal (1-2 days install) | Months of construction |
Prefab ADUs: What to Know
Prefab Advantages
- •Speed: Factory builds while permits process; on-site install in 1-2 days
- •Fixed pricing: Know your costs upfront; no surprise change orders
- •Weather-independent: Built indoors regardless of season
- •Consistent quality: Factory QC processes eliminate job-site variables
- •Less disruption: Your yard isn't a construction zone for months
Prefab Limitations
- •Site access critical: Needs crane access (40+ ft boom typically)
- •Limited customization: Choose from set floor plans and finishes
- •Transport constraints: Max width ~14 ft, length ~60 ft for transport
- •Deposit required: Often 30-50% upfront before manufacturing
- •Long lead times: 2-4 month factory queue common
Critical: Site Access for Prefab
This is the most common deal-breaker for prefab. Your site needs:
Minimum Access Requirements
- Truck access: Semi-truck needs to reach within 50-100 ft of installation site
- Crane setup: Stable, level area for crane (often street or driveway)
- Clear path: No power lines, trees, or obstacles in lift path
- Overhead clearance: 25-40+ ft vertical clearance for crane boom
- Street permits: May need city permit for crane/truck staging
Pro tip: Most prefab companies offer free site assessments. Get this done early—it takes 15 minutes and immediately rules in or out the prefab option.
Stick-Built ADUs: What to Know
Stick-Built Advantages
- •Unlimited customization: Any size, shape, layout, materials
- •No access restrictions: Materials come in small loads
- •Adapt to site: Build around trees, slopes, existing structures
- •Smaller deposits: Pay as work progresses
- •Local contractors: Build relationships, support local economy
Stick-Built Challenges
- •Longer timeline: 6-12 months typical, weather dependent
- •Cost uncertainty: Change orders and surprises common
- •Contractor quality varies: Must vet carefully
- •Project management: More decisions and oversight needed
- •Site disruption: Months of construction activity in your yard
Timeline Comparison
Prefab Timeline (3-6 mo)
Stick-Built Timeline (6-12 mo)
Which Should You Choose?
Choose Prefab If:
Choose Stick-Built If:
Frequently Asked Questions
Is prefab lower quality than stick-built?
No—often the opposite. Factory conditions allow better quality control, precision cuts, and protection from weather during construction. Reputable prefab companies use the same or better materials than typical site-built construction.
Can I customize a prefab ADU at all?
Yes, but within limits. Most offer choices of floor plans (5-20 options), exterior finishes, cabinet colors, flooring, and fixtures. What you can't do is redesign the floor plan or significantly change dimensions.
What if my site fails the access assessment?
Sometimes access can be created by temporarily removing fences, trimming trees, or using longer-boom cranes. If truly impossible, stick-built becomes your only option—or consider if prefab panels (vs. whole units) could work.
Do banks finance prefab ADUs differently?
Financing can be slightly different. Prefab requires larger upfront deposits (30-50%) before the unit exists. Some lenders prefer stick-built where they can do construction draws. Check with your lender early.
Ready for the Next Step?
Now that you understand construction methods, it's time to determine the right size for your ADU based on your lot, regulations, and intended use.