Hillsborough is known for its grand estates, expansive lots, and refined architectural standards. In this prestigious community, every addition to your property must meet the highest expectations of design, quality, and discretion.

As homeowners look to accommodate multi-generational living, add private guest quarters, or create high-end home offices, Accessory Dwelling Units (ADUs) have become a popular solution. At Royalty Builders, we specialize in luxury ADU construction in Hillsborough—with careful attention to the town’s zoning rules, aesthetics, and custom-home environment.

Whether you’re converting a garage, building a detached guesthouse, or adding a fully self-contained wing, we guide you through the process with integrity, precision, and white-glove service.

🛠️ Full-Service ADU Design + Build in Hillsborough

We are a fully integrated design-build firm that handles the entire ADU process—from concept and feasibility to permitting, construction, and handoff. Our goal is to make the experience seamless, so you can focus on vision while we handle every detail.

✅ Custom Design Planning – We create ADU designs that reflect the architecture and proportions of your main home
✅ Property & Code Assessment – We analyze lot size, slope, access, drainage, and utility systems to ensure feasibility
✅ Permit Navigation – Hillsborough has its own review board and design standards—we work closely with the Town
✅ Luxury Construction & Finishes – From masonry to millwork, we deliver exceptional craftsmanship
✅ Turnkey Delivery – Move-in ready and fully code-compliant with a clean, elegant finish

In Hillsborough, every project must uphold the neighborhood’s integrity—and that’s exactly what we do.

🧱 Types of ADUs We Build in Hillsborough

Because Hillsborough does not permit multi-family dwellings or small-lot development, all ADUs must comply with single-family zoning and architectural compatibility. We build:

• Detached ADUs – Ideal for guesthouses, in-law suites, or private retreats

• Attached ADUs – Seamless extensions to your home with separate entries

• Garage Conversions – Elegant transformations of existing structures

• Above-Garage ADUs – Perfect for preserving landscape and providing elevation views

• High-End Junior ADUs (JADUs) – Efficient, code-compliant units within your existing home

All our ADUs are custom-designed, matching your home’s scale, materials, and architectural character.

📍 Why Build an ADU in Hillsborough?

Even in a community known for spacious properties, there’s growing interest in private, flexible-use spaces that serve modern living needs. An ADU gives you:

✔️ Private Living for Family or Staff – Independent yet nearby housing for relatives or caretakers
✔️ Guest Accommodations – Comfortable, upscale lodging for visiting friends or extended stays
✔️ A Professional Work Space – Create a high-end office or studio steps from home
✔️ Future-Proof Your Property – More square footage, more value, and more flexibility
✔️ Increased Long-Term ROI – ADUs are increasingly attractive to luxury homebuyers seeking versatility

Hillsborough’s large lots and strong property values make ADUs a strategic and lifestyle-enhancing investment.

💲 ADU Construction Costs in Hillsborough

Due to the high standards of design, materials, and site conditions in Hillsborough, ADU costs here are generally on the higher end of the spectrum:

• Garage Conversions: typically $150,000–$225,000+

• Detached ADUs: range from $300,000–$600,000+, depending on size and materials

• Attached ADUs: usually $250,000–$450,000

• Above-Garage Units: start around $325,000+, depending on structural complexity

📌 We provide line-item estimates, ensure full code compliance, and assist with budgeting options—including phased development or design-first planning.

📝 Permits for ADU Construction in Hillsborough – What You Need to Know

Unlike many other cities, Hillsborough has specific and elevated architectural standards for all additions, including ADUs. Building here requires a thoughtful and compliant approach—and our team is experienced in navigating it successfully.

What to expect:

🔹 Zoning Compliance
Hillsborough permits one ADU and/or one Junior ADU (JADU) per lot in most residential zones. ADUs must meet lot coverage, height, and placement requirements, including restrictions on visibility from public roads.

🔹 Architectural Design Review
The Town of Hillsborough requires ADUs to match the architectural style of the primary residence. Royalty Builders prepares and submits renderings, elevations, and materials boards to comply with this requirement.

🔹 Planning & Building Permits
We handle all city submittals, including:

• Site plan

• Floor plans

• Exterior elevations

• Title 24 (energy compliance)

• Structural engineering and grading (if required)

🔹 Construction Inspections
All projects are subject to inspections during construction. We manage scheduling and walk-throughs to ensure full compliance.

✅ Important: Hillsborough adheres to California’s 60-day rule for permit approvals but may require additional design board input. Our experience with the Town allows us to streamline this process and avoid unnecessary revisions.

👷 Why Choose Royalty Builders for Your Hillsborough ADU?

In Hillsborough, quality, privacy, and architectural integrity are non-negotiable. Royalty Builders is the trusted name for high-end, code-compliant ADUs that meet the expectations of discerning homeowners.

• 🧱 Custom, Estate-Caliber Designs

• 🧭 Local Permitting Expertise

• 🛠️ Superior Construction & Materials

• 🏡 Architectural Matching & Landscaping Considerations

• 📞 Concierge-Level Client Communication

Our team treats every Hillsborough ADU as a signature project—built to elevate your lifestyle and enhance your home.

❓ FAQ – ADU Services in Hillsborough

Q: Can I build a rental ADU in Hillsborough?
A: Yes. Long-term rentals (30+ days) are allowed. Short-term vacation rentals are generally not permitted.

Q: Can my ADU have a full kitchen and separate utilities?
A: Yes. Full kitchens are allowed. Separate utilities are optional and depend on use preferences.

Q: Do I need to match my home’s exterior?
A: Yes. The Town requires ADUs to match the existing architectural character—including roofing, siding, and materials.

Q: How long does the approval process take?
A: Most ADU permits are processed within 60–90 days, though Hillsborough may require additional review based on design or visibility.

📞 Contact Us – Start Your Hillsborough ADU Project Today

Your Hillsborough estate deserves the finest craftsmanship and most thoughtful design. Whether you’re building for family, hosting, or future flexibility, we’ll help you create an ADU that fits your home—and your life—perfectly.

📞 Call us today and schedule your private consultation.

At Royalty Builders, we build more than just ADUs. We build seamless, sophisticated spaces worthy of Hillsborough’s legacy of excellence.