In Castro Valley, where scenic charm meets suburban convenience, many homeowners are realizing the value of building an Accessory Dwelling Unit (ADU). Whether it’s to house aging parents, create a rental unit, or add an independent workspace—ADUs provide flexible, high-return solutions without sacrificing your location or lifestyle.

At Royalty Builders, we offer full-service ADU design and construction tailored to your needs. From your first consultation to the final inspection, we bring quality craftsmanship, transparent pricing, and local expertise to every project.

Types of ADUs We Build in Castro Valley

Every property in Castro Valley has unique potential, and our team helps you unlock it with the ADU type that fits your goals, layout, and budget. Whether you’re looking to convert an existing space or build something brand new—we’ve done it all.

We specialize in:

• Detached ADUs – Freestanding backyard homes perfect for privacy, rentals, or guests

• Attached ADUs – Seamlessly integrated with your existing structure

• Garage Conversions – Turn an underused garage into a fully livable unit

• Above-Garage ADUs – Great for smaller lots that need vertical expansion

• Basement ADUs – Convert existing space into a legal, rentable suite

All ADUs are designed to meet Castro Valley’s building standards and customized for your specific needs.

Full-Service ADU Design + Build in Castro Valley

Royalty Builders handles every stage of the ADU journey under one roof. Our design-build model means less stress for you—we manage the architects, engineers, permits, and construction, all in-house. You’ll get one experienced team, one point of contact, and a streamlined process.

Our services include:

• Property analysis and feasibility studies

• Custom architectural planning and 3D design

• Structural and energy compliance documentation

• Permit application and coordination with Alameda County

• Complete construction and project management

• Final walkthrough, utility setup, and occupancy

You get a turnkey experience that delivers beauty, functionality, and peace of mind.

How Much Does It Cost to Build an ADU in Castro Valley?

ADU pricing depends on design, square footage, site conditions, finishes, and whether you’re converting or starting from scratch. At Royalty Builders, we provide fully transparent quotes—so you always know where every dollar goes.

Typical ADU pricing in Castro Valley:

• Garage Conversion: $120,000 – $170,000

• Attached ADU: $180,000 – $290,000

• Detached ADU: $200,000 – $350,000+

• Above-Garage ADU: $220,000 – $360,000+

We also assist with exploring financing options and help you make the smartest investment for your property and goals.

Permits for ADU Construction in Castro Valley – What You Need to Know

Castro Valley falls under the jurisdiction of Alameda County, which follows California’s updated ADU laws. However, there are still site-specific rules around setbacks, height, unit size, and utility connections. That’s where we come in.

Our permitting team handles:

• Site analysis based on zoning and lot layout

• Submission of architectural and engineering plans

• Managing plan checks, resubmittals, and corrections

• Communication with Alameda County Planning & Building Department

• Final inspections and occupancy certificate

We take care of the paperwork and timelines, so you can focus on the vision.

Why Build an ADU in Castro Valley?

Castro Valley offers the perfect mix of tranquility, family-friendly neighborhoods, and access to the entire Bay Area. With increasing property values and high demand for rental housing, ADUs have become one of the most strategic ways to grow your living space—and your equity.

Here’s why homeowners are building ADUs in Castro Valley:

• 🏠 Flexible living – for in-laws, older kids, guests, or even live-in care

• 💼 Home office or studio – work in peace, just steps from home

• 💰 Rental income – tap into local housing demand

• 📈 Boost property value – ADUs are a strong selling point

• 🔄 Future-proofing – age in place or create generational housing options

Now, with supportive state laws and flexible county guidelines, it’s easier than ever to bring your ADU project to life in Castro Valley.

Frequently Asked Questions – ADUs in Castro Valley

Q: What’s the maximum size I can build for an ADU in Castro Valley?
A: Most detached ADUs can be up to 1,200 sq. ft., depending on your lot. Our team can help determine exact limits based on your property.

Q: Do I need to provide parking for my ADU?
A: In many cases, no. State law exempts parking requirements for ADUs near public transit or when converting an existing space.

Q: How long will my ADU project take?
A: Timelines vary, but most ADUs take 6–10 months from initial design through construction and final inspection.

Q: Can I rent out my ADU legally?
A: Yes! Castro Valley ADUs can be used for long-term rentals. We ensure full code compliance so you can lease your unit with confidence.

Contact Royalty Builders – Your Castro Valley ADU Experts

Thinking about adding more space, value, and flexibility to your Castro Valley home? Let’s build your vision—together. Royalty Builders is your trusted partner for high-quality, code-compliant ADUs from start to finish.

📞 Contact us today and schedule your free ADU consultation in Castro Valley.

More space. More value. More possibilities—with Royalty Builders.