Prefab vs. Custom ADUs: Which Is Right for You? (2025 Central Oregon Guide)

Greg Powell
2 days ago
3 min read

As more Central Oregon homeowners explore the benefits of building an Accessory Dwelling Unit (ADU), one big question always comes up early in the process:

Should you choose a prefab ADU or build a custom one?

Both options can add tremendous value, flexibility, and rental potential to your property — but the right choice depends on your budget, timeline, lot conditions, and long-term plans.

This guide breaks down the differences, costs, pros, and drawbacks of each so you can make an informed decision in 2025.

What Is a Prefab ADU?

A prefab (prefabricated) ADU is a pre-designed, factory-built unit that’s transported to your property and installed on-site. Think of it as a “turnkey” ADU option.

Prefab units come in various sizes — studios, 1-bedrooms, even small 2-bedrooms — with finishes and layouts chosen upfront.

Benefits of Prefab ADUs

Faster build time: Often installed in 8–16 weeks after permits.
Predictable pricing: Set floor plans = fewer change orders, fewer surprises.
Factory precision: Weather-controlled construction improves durability and energy efficiency.
Less on-site disruption: Ideal for busy neighborhoods or smaller lots.
Lower labor costs: Much of the work is done off-site.

Drawbacks of Prefab ADUs

Limited customization: You can pick finishes, but you can’t redesign the layout.
Transportation challenges: Not ideal for tight, sloped, or forested lots.
Site work still needed: Foundation, utilities, and crane placement can increase costs.
HOA/zoning restrictions: Some neighborhoods don’t allow specific prefab models.

What Is a Custom ADU?

A custom ADU is designed from scratch with an architect or designer to fit your property’s unique characteristics.

Benefits of Custom ADUs

Fully personalized: Tailor the layout, materials, roofline, windows — everything.
Perfect for complex lots: Slopes, small lots, trees, and unique setbacks are easier to accommodate.
Higher long-term value: Custom design often leads to better resale and rental performance.
Easier to match your main home: Great for aesthetics, HOAs, or long-term multi-gen living.

Drawbacks of Custom ADUs

Longer timeline: Typically 6–12+ months, depending on design and permits.
Higher upfront costs: Architectural fees, engineering, and custom finishes add up.
More decisions: You’ll be more involved throughout the design and construction phases.
More on-site disruption: Construction noise and staging happen right at your home.

Cost Comparison (2025 Central Oregon Estimates)

Type	Typical Cost	Timeline	Best For
Prefab ADU	$140,000–$240,000 (installed)	2–4 months	Faster projects, predictable pricing, simpler lots
Custom ADU	$200,000–$350,000+	6–12+ months	Complex lots, high-end finishes, exact design control

Note: Costs vary based on size, utilities, foundation requirements, and labor conditions in Central Oregon.

Which One Is Right for You?

Choose a Prefab ADU if…

You want a faster, predictable project.
Your lot is flat and accessible.
You prefer a streamlined, low-stress process.
You’re building the ADU primarily for rental income.
Budget certainty is a top priority.

Choose a Custom ADU if…

You want an ADU that blends seamlessly with your home.
Your lot has slopes, trees, or septic challenges.
You’re planning for long-term family use (aging parents, adult children).
Design flexibility is important to you.
You want the highest possible property value boost.

Prefab vs. Custom: The Central Oregon Perspective

Demand for ADUs in Bend, Redmond, and Deschutes County is rapidly growing, driven by new state legislation, housing shortages, and rising home values.

In Central Oregon specifically:

Prefab ADUs thrive in new subdivisions, flat urban lots, and areas with easier utility access.
Custom ADUs often make more sense in rural areas, older neighborhoods, and properties on septic systems where design must adapt to infrastructure and wildfire regulations.

There’s no one-size-fits-all answer to the prefab vs. custom ADU debate. The right option depends on your goals:

Speed and budget? Prefab.
Design-specific needs or tricky lot? Custom.
Long-term multigenerational home plan? Often custom.
Rental-focused investment? Prefab is a strong contender.

Whichever route you choose, 2025 is one of the best years yet for Central Oregon homeowners to build an ADU thanks to updated laws, streamlined permitting, and rising rental demand.

FAQs

Q: Are prefab ADUs cheaper than custom ADUs?

Usually yes. Prefab ADUs tend to be 15–25% cheaper, depending on finishes and site conditions.

Q: Do both types require permits?

Yes. Whether prefab or custom, you must still go through building, electrical, plumbing, and zoning approvals.

Q: Which option builds equity faster?

Prefab ADUs can produce rental income more quickly, but custom ADUs often yield higher long-term property value.

Q: Are prefab ADUs allowed everywhere?

Not always. Check zoning, HOAs, and wildfire zones for limitations.

Q: Can I customize a prefab ADU?

Only to an extent — mostly finishes, colors, appliances, and small layout options.