Building an ADU in Mission Viejo

Accessory Dwelling Units (ADUs) — also called granny flats, casitas, or backyard homes — have become one of the smartest ways for Mission Viejo homeowners to create extra space, boost property value, and generate rental income. But before starting your ADU project, it’s important to understand the local rules, requirements, and what the process actually looks like in our city.

Below is a complete guide to ADU regulations, design considerations, and step-by-step tips — written for Mission Viejo homeowners thinking about adding one to their property.

What Is an ADU and Why They’re So Popular in Mission Viejo

An ADU is a self-contained residential unit on the same lot as your main home. It can be attached, detached, or converted from an existing space like a garage.In Mission Viejo, ADUs are increasingly popular for:

• Rental income – a steady long-term lease or housing for family members.

• Multigenerational living – giving aging parents or adult children privacy while staying close.

• Property value growth – ADUs can add 20–30% to your home’s market value.

• Flexible use – guest suite, home office, or short-term rental (with some limitations).

ADU Regulations in Mission Viejo (2025 Update)

Mission Viejo follows California’s state ADU laws but also adds local requirements to fit community design standards. Here’s what you need to know:

1. Zoning & Eligibility

• ADUs are allowed on any residential-zoned lot with an existing single-family home.

• No minimum lot size requirement — even small parcels can qualify.

• You may build one full ADU and one Junior ADU (JADU) on a single-family lot.

2. ADU Types

• Detached ADU – A separate unit built in the backyard (most common).

• Attached ADU – An extension connected to the main home.

• Garage Conversion – Transforms an existing garage into a livable unit.

• Junior ADU (JADU) – Built within the main home, typically up to 500 sq ft.

3. Size & Height Limits

• Detached or attached ADUs can go up to 1,200 sq ft depending on lot and design.

• JADUs are capped at 500 sq ft.

• Height limit typically 16–18 ft for single-story detached ADUs.

4. Setbacks

• Minimum 4 ft from side and rear property lines.

• Front setbacks usually match the main home’s zoning requirements.

5. Parking

• One parking space may be required for new ADUs unless exemptions apply:

  • Within ½ mile of public transit

  • Converted from an existing structure (like a garage)

  • In a historic district

  • Within an existing primary dwelling footprint

6. Owner Occupancy

• For detached ADUs, owner occupancy is not required until at least 2025 under state law.

• For Junior ADUs, the owner must live in either the main home or the JADU.

7. Design & HOA Guidelines

• Mission Viejo promotes ADUs that match the main home’s architectural style (color, roofline, and materials).

• If your home is part of an HOA, you’ll need to check your association’s ADU policy — HOAs cannot prohibit ADUs but can enforce design review.

• The Mission Viejo Environmental Association (MVEA), for example, requires homeowners to submit ADU design plans for architectural approval before construction.

Permitting & Construction Process

Building an ADU in Mission Viejo follows an administrative permit process — meaning no public hearings or planning commission approvals if you meet the rules.

Here’s how the process usually goes:

1. Feasibility CheckConfirm zoning, lot setbacks, and utility connections.

2. Concept DesignWork with a designer or licensed general contractor to plan layout, exterior style, and finishes.

3. Permit SubmissionApply through the City of Mission Viejo’s Building Division. Include site plan, structural drawings, and energy calculations.

4. Plan Review & ApprovalThe city must approve compliant ADU plans within 60 days of submittal.

5. Construction PhaseDepending on size and complexity, construction takes 3–6 months.

6. Final Inspection & Occupancy CertificateOnce completed, the city inspects and issues occupancy approval.

Common Questions from Mission Viejo Homeowners

Can I rent my ADU on Airbnb?

Short-term rentals are limited. Most ADUs are approved for long-term rentals (30+ days). Check your HOA rules and the city’s short-term rental ordinance before listing.

Will adding an ADU affect my property taxes?

Yes — your property’s assessed value will increase, but only for the new unit, not your entire property.

Do I need separate utility connections?

Not always. Some ADUs share utilities with the main home; others install separate meters for independence (especially for rentals).

How much does it cost to build an ADU in Mission Viejo?

Typical construction costs range from:

• Garage conversion: $120K–$170K

• Attached ADU: $180K–$250K

• Detached custom ADU: $220K–$350K+Final pricing depends on finishes, foundation type, and site conditions.

Why Build an ADU Now

• Fast approvals – State law mandates a 60-day review.

• Strong rental market – High demand for housing in South OC.

• Equity growth – ADUs typically add significant resale value.

• Family flexibility – Perfect for aging parents or adult kids.

How First Round Construction Can Help

At First Round Construction, we specialize in ADU design and build projects across Mission Viejo and South Orange County. Our team handles everything from initial feasibility and design concepts to permits, construction, and final finishes — ensuring your project meets city requirements and blends seamlessly with your home’s style.

What we provide:

• Free on-site consultation and feasibility check

• Detailed cost breakdowns and design renderings

• Permit management and HOA coordination

• Licensed, bonded, and insured construction

Final Thoughts

Mission Viejo homeowners have a unique opportunity: build additional living space, generate income, and increase property value — all within a streamlined regulatory framework.

Whether you’re planning a cozy backyard studio or a full guest house, understanding the local ADU rules is the first step toward a smooth and successful build.

Thinking about an ADU in Mission Viejo?👉 Contact First Round Construction for a free ADU consultation — we’ll help you turn your space into something extraordinary.