Written by Pro Value Contracting | Published on July 2025
A standard ADU in California can be up to 1,200 square feet, while a Junior ADU is capped at 500 square feet and must be built within your existing home’s footprint. Both options allow homeowners to add rental income, house family members, or increase property value. This article covers the rules, costs, permitting process, and practical differences between the two so you can choose the right path for your San Diego property.
Understand What Each Unit Type Actually Means
ADU stands for Accessory Dwelling Unit. It is a secondary housing unit on a single-family or multifamily residential lot. It can be attached to your home, detached in the backyard, or created by converting a garage or other structure.
A Junior ADU, or JADU, is a smaller version that must be entirely within the walls of your primary residence. Think of converting a large bedroom, an attached garage, or an underused bonus room into a self-contained living space.
The biggest practical difference is this: a JADU cannot be a standalone structure. It lives inside your existing home. A standard ADU can stand completely on its own in your backyard.
Compare the Core Rules Side by Side
California state law sets the baseline rules for both unit types. Local jurisdictions like the City of San Diego can add some requirements but cannot be more restrictive than state law on key points.
| Feature | Standard ADU | Junior ADU (JADU) |
|---|---|---|
| Maximum Size | 1,200 sq ft (attached or detached) | 500 sq ft |
| Location | Attached, detached, or garage conversion | Must be within existing home structure |
| Kitchen Requirements | Full kitchen allowed | Efficiency kitchen only (no gas range required) |
| Separate Entrance | Required | Required (may share interior access) |
| Owner Occupancy | Not required by state law (varies locally) | Owner must live in primary home or JADU |
| Parking Requirement | Often waived within half mile of transit | No additional parking required |
| Number Allowed Per Lot | Up to 2 ADUs on single-family lot | 1 JADU per single-family lot |
In San Diego, the city has adopted streamlined permit review for both unit types, which has made the process faster than it was even three or four years ago.
Explore the Cost Differences Between ADUs and JADUs
Cost is usually the deciding factor for most homeowners. A Junior ADU is almost always cheaper because you are working within your existing structure. You are not pouring a new foundation or framing new walls from scratch.
| Unit Type | Typical Cost Range (San Diego) | Main Cost Drivers |
|---|---|---|
| Junior ADU (JADU) | $40,000 to $120,000 | Kitchen conversion, bathroom addition, separate entrance |
| Attached ADU | $100,000 to $250,000 | Addition construction, mechanical systems, permits |
| Detached ADU | $150,000 to $400,000+ | Foundation, framing, full utility connections |
| Garage Conversion ADU | $60,000 to $150,000 | Insulation, HVAC, windows, kitchen, bathroom |
These ranges reflect San Diego labor and materials costs in 2025. Costs vary depending on finishes, site conditions, and how much existing plumbing or electrical is already in place.
Pro Value Contracting works with homeowners across San Diego on both standard ADUs and JADUs. We can walk you through which type fits your budget and existing layout before you commit to anything.
Know the Owner Occupancy Rules That Apply in San Diego
This is where JADUs have a significant restriction that standard ADUs do not always carry. California state law requires that if you have a JADU on your property, the owner must live in either the primary home or the JADU itself. You cannot rent out both units and live elsewhere.
Standard ADUs are different. California law generally does not require owner occupancy for standard ADUs, though this can vary if local ordinances were grandfathered in before 2020.
Here is what this means practically for San Diego property owners:
- If you plan to live on the property long-term, a JADU is a strong option for generating rental income from a smaller, lower-cost unit.
- If you want the flexibility to rent out the entire property someday, a standard ADU gives you more options.
- If you are an investor who does not plan to live on-site, a JADU may not be the right fit due to the owner-occupancy requirement.
- A single-family lot in San Diego can have one JADU and up to two standard ADUs at the same time, which is a powerful combination for income generation.
Understand the Permitting Process in San Diego
The City of San Diego has invested in making ADU and JADU permitting more accessible. Both unit types require building permits, but the city offers pre-approved ADU plans through its standard plan program, which can cut weeks off your approval timeline.
Key steps in the San Diego permitting process include:
- Confirm your lot’s zoning allows an ADU or JADU. Most single-family zones in San Diego do.
- Check for any deed restrictions, HOA rules, or coastal zone overlays that may apply to your specific address.
- Submit plans through the city’s online Development Services portal. JADUs tend to have simpler plan sets since they involve fewer structural changes.
- Receive plan check review. San Diego targets a 30-day review for ADU applications.
- Pull the permit and begin construction with a licensed contractor.
- Schedule inspections at foundation, framing, electrical, and final stages.
- Receive your certificate of occupancy before the unit is rented or occupied.
JADUs that involve only interior work and do not alter the footprint of the home often have a simpler plan set and lower permit fees. San Diego permit fees for JADUs typically range from $3,000 to $8,000 depending on project scope.
Identify Which Option Makes Sense for Your Property
The right choice depends on your property, your goals, and your timeline. There is no single answer that works for every San Diego homeowner.
A JADU is likely the better fit if:
- You have a large bedroom, attached garage, or bonus room you are not fully using.
- Your budget is under $120,000 and you want to keep costs manageable.
- You plan to live on the property and want to offset your mortgage with rental income.
- Your lot is small and does not have room for a detached structure.
- You want to house an aging parent or adult child nearby with some privacy.
A standard ADU is likely the better fit if:
- You have a large backyard with enough setback room to build a detached structure.
- You want a fully independent unit with no shared walls or interior access to the main home.
- You want the flexibility to rent both units without living on-site.
- You are thinking long-term about property value and want a permanent addition that appraisers treat as separate square footage.
Pro Value Contracting has helped San Diego homeowners evaluate both options based on their actual property conditions, not just general rules. Reach out before you make any decisions.
FAQs on ADUs and Junior ADUs in California
Can I build both an ADU and a JADU on the same property in San Diego?
Yes. California law allows a single-family property to have one JADU plus up to two standard ADUs at the same time. This is one of the most powerful ways to maximize rental income on a single lot in San Diego.
Does a Junior ADU need a full kitchen?
No. A JADU only requires an efficiency kitchen, which typically includes a small sink, a countertop cooking appliance like a hot plate or induction burner, and a mini-fridge. A full gas range and oven are not required, which simplifies the construction and keeps costs lower.
Will adding an ADU or JADU raise my property taxes in California?
Under California’s Prop 13, adding a new structure triggers a reassessment only for the value of the addition itself. Your existing home’s assessed value stays the same. The new ADU or JADU gets added to your assessment separately, which typically increases annual property taxes by a modest amount relative to the income potential.
How long does it take to build a JADU in San Diego?
A straightforward JADU conversion from an existing bedroom or attached garage can take 3 to 6 months from permit submission to final inspection. More complex projects involving structural changes or new bathrooms can take 6 to 9 months. Using the city’s pre-approved plan sets can speed up permit approval significantly.
Do I need to add a separate utility meter for a JADU?
No. California law does not require a separate utility meter for a JADU. The unit typically shares meters with the primary residence. Standard ADUs may or may not require separate meters depending on local utility rules and project scope.
What setbacks apply to detached ADUs in San Diego?
California state law requires a minimum 4-foot rear and side setback for detached ADUs up to 800 square feet. Larger detached ADUs may be subject to local setback rules. San Diego follows the state minimums in most zones, but you should verify your specific parcel’s requirements through the city’s development services office.
Wrap Up and Next Steps
The core difference between an ADU and a Junior ADU comes down to size, location, and flexibility. JADUs are cheaper and faster to build but require owner occupancy and must stay inside your existing home. Standard ADUs cost more but give you a fully independent unit with fewer restrictions on how you use it.
If you are a San Diego homeowner thinking about adding either type of unit, Pro Value Contracting can help you assess your property, understand local requirements, and plan a project that fits your goals and budget. Call us today at (888) 508-6580 to schedule a consultation and get started on the right path.