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Not Every Property Can Support an ADU — and Not Every “Expert” Knows the Law
Building an ADU in California can be a smart investment—but for many homeowners, it turns into a costly and frustrating experience. Why? Because too often, city planners, designers, and builders overlook or misunderstand the state laws designed to protect homeowners. Without the right team guiding you through the process, this lack of knowledge can lead to denied plans, costly redesigns, unexpected utility upgrades, and months of delays.
The Most Common Mistakes Homeowners Make:
The Most Common Mistakes Homeowners Make:
Trusting city staff or generic contractors without verifying their ADU expertise
Submitting plans before fully understanding state law vs. local restrictions
Relying on outdated zoning maps or bad feasibility advice
Paying for design and engineering before confirming buildability
Not pre-checking for utility upgrades, easements, or fire department issues
WHAT IS AN ADU?
WHAT IS AN ADU?
An Accessory Dwelling Unit (ADU) is a self-contained residential unit that’s legally part of a single-family or multi-family property. ADUs must include a kitchen, bathroom, and living space. They can be detached, attached, or converted from existing space (like a garage or basement). Basically an apartment in your property that can generate cashflow
TYPES OF ADU'S
WHAT IS A CONVERSION ADU?
WHAT IS A CONVERSION ADU?
A Conversion ADU is a secondary residential unit created by converting existing permitted space—such as a portion of a house, garage, barn, or other enclosed structure—into a separate, code-compliant living area.
KEY CHARACTERISTICS:
KEY CHARACTERISTICS:
Created from existing floor area (not new construction)
Can be part of the main house, an attached garage, detached garage, or outbuilding
May include its own entrance, kitchen, bathroom, and living space
No minimum or maximum square footage limits, aside from fire/life safety compliance
WHAT IS A JADU?
WHAT IS A JADU?
A Junior Accessory Dwelling Unit (JADU) is a compact, legally defined living unit created within the existing walls of a single-family home. It’s often formed by converting an interior bedroom, den, or attached garage space into a private, rentable unit.
KEY CHARACTERISTICS:
KEY CHARACTERISTICS:
Size Limit: Maximum of 500 square feet
Location: Must be part of the existing primary residence (not a detached structure)
Kitchen: May include a kitchenette instead of a full kitchen
Bathroom: Can share a bathroom with the main home
Occupancy: Requires owner-occupancy on the property or placement into a land trust
Fire Rating: Typically does not require a 1-hour fire separation between units (check with local jurisdiction for confirmation)
WHAT IS A GROUND-UP ADU?
WHAT IS A GROUND-UP ADU?
A Ground-Up ADU is a new, detached structure built on your property—either constructed onsite from the foundation up or installed as a prefabricated unit. It offers the greatest flexibility in layout, finishes, and privacy—but also comes with the most technical and permitting requirements.
KEY CHARACTERISTICS:
KEY CHARACTERISTICS:
New Construction or Prefab: Built entirely from scratch or delivered as a factory-built modular or panelized unit
Detached: Separate from the main home with its own entry, utilities, and livable space
Full Living Unit: Includes kitchen, bathroom, and sleeping/living area
Location-Based Limits:
Minimum cities must allow: 800 sq. ft., up to 16 ft. in height
Maximum allowed by state law: 1,200 sq. ft. (some cities allow more)
Minimum setbacks: 4 feet from rear and side property lines
COMMON REQUIREMENTS:
COMMON REQUIREMENTS:
Depending on your property and local conditions, ground-up ADUs often require:
Soils report (especially for sloped or unstable lots)
Survey (to confirm property lines, easements, and compliance)
Solar PV system (required by California Energy Code for new detached dwellings)
Electrical upgrades (panel capacity and service upgrades)
Water/sewer line extensions or upsizing
Grading & drainage plans (for larger units or sloped lots)
Fire sprinklers (may be required depending on fire access or hydrant proximity and if the existing main residence is equipped with them )
Conversion ADU vs Junior ADU (JADU) vs Ground-Up ADU (Detached)
Size Limits:
CONVERSION ADU: Can exceed 500 sq. ft.
JADU:Max 500 sq. ft.
GROUND UP ADU:Up to 1,200 sq. ft. (minimum required: 800 sq. ft.)
Location
CONVERSION ADU: ADU Within existing structure (house, garage, barn)
JADU: Inside the primary home only
GROUND UP ADU: Detached, new structure or prefab
Owner-Occupancy
CONVERSION ADU:Not required under state law
JADU: Required, unless SB-9 or land trust is used
GROUND UP ADU:Not required
Detached Allowed?
CONVERSION ADU: Yes (e.g. garage conversion)
JADU: No — must be within the home
GROUND UP ADU:Yes — entirely new standalone unit
Common Requirements
CONVERSION ADU: May need parking, egress upgrades
JADU:Simple conversion; limited to interior
GROUND UP ADU: May require solar, grading, survey, soils, utilities, fire
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