DADU vs ADU vs JADU: Every ADU Type Explained

DADU vs ADU: The Quick Answer

Searching “DADU vs ADU” and drowning in acronyms? Here is what you need to know in 30 seconds.

ADU stands for Accessory Dwelling Unit. It is the umbrella term for every secondary housing unit on a residential lot. A DADU is a Detached Accessory Dwelling Unit, one specific type of ADU that sits as a standalone structure in your yard. All DADUs are ADUs, but not all ADUs are DADUs.

California recognizes four types of ADUs: detached (DADU), attached (AADU), garage conversion, and junior (JADU). They range from $40,000 to over $500,000, from 2 months to 14 months, and from 500 to 1,200 square feet. The right one depends on your lot, your budget, and what you want the unit to do.

This guide covers each type in detail: specs, Bay Area costs, timelines, and the scenarios where each one makes sense.

ADU Types in California: Side-by-Side Comparison

Before the deep dives, here is everything in one table.

Factor	DADU (Detached)	AADU (Attached)	Garage Conversion	JADU (Junior)
What It Is	Standalone structure on your lot	Addition connected to your home	Converted garage space	Unit within existing home
Max Size	1,200 sqft	1,200 sqft or 50% of home	Limited by garage footprint	500 sqft
Bay Area Cost	$250,000-$500,000+	$150,000-$350,000	From $120,000	$40,000-$80,000
Kitchen	Full kitchen required	Full kitchen required	Full kitchen required	Efficiency kitchen allowed
Bathroom	Own bathroom required	Own bathroom required	Own bathroom required	Can share with main house
Utilities	New connections needed ($15K-$30K)	Can share with main house	Can share with main house	Shares with main house
Privacy	Full separation	Shared wall(s)	Varies	Within main home
Timeline	8-14 months	6-10 months	4-6 months	2-4 months
Owner-Occupancy	Not required	Not required	Not required	Only if sharing bathroom
Best For	Rental income, in-law suites	Smaller lots, family use	Budget-friendly full ADU	Lowest budget, fastest timeline

Now let’s break each one down.

What Is an ADU? The Umbrella Term Explained

ADU stands for Accessory Dwelling Unit. The California Department of Housing and Community Development (HCD) defines it as a residential dwelling unit that provides complete, independent living facilities for one or more persons, located on a lot with an existing or proposed primary residence.

Think of “ADU” the way you think of “vehicle.” Sedans, SUVs, trucks, and motorcycles are all vehicles. DADUs, AADUs, garage conversions, and JADUs are all ADUs. The term itself does not tell you about size, structure, or whether the unit is attached or detached. It just means a second dwelling on a residential lot.

You will also hear people call ADUs “granny flats,” “in-law units,” “backyard cottages,” or “secondary units.” Same concept, different names. California law uses “ADU” as the official term.

What Does DADU Stand For?

DADU stands for Detached Accessory Dwelling Unit. The term was popularized by AARP’s “ABCs of ADUs” research and has become the standard shorthand for any standalone ADU that shares no walls with the primary home.

A DADU is a ground-up construction project. You are building a small home from scratch: foundation, framing, roofing, full mechanical/electrical/plumbing systems, and all interior finishes. That is why it is the most expensive ADU type, and also the most valuable.

For a full deep dive, see our guide on what a DADU is and how it works.

DADU Specs at a Glance

• Size: Up to 1,200 sqft for detached units on single-family lots
• Structure: Own foundation, walls, roof, entrance, kitchen, and bathroom
• Utilities: Requires independent connections for water, sewer, and electrical (typically $15,000-$30,000 on top of the build cost)
• Cost: $250,000-$500,000+ in the Bay Area
• Owner-occupancy: Not required under California law (AB 976 removed this requirement permanently as of January 1, 2024)
• Timeline: 8-14 months from design through move-in

When a DADU Is the Right Call

DADUs command the highest rents of any ADU type. Tenants pay a premium for a freestanding unit with real privacy: their own entrance, their own yard space, no shared walls. In the Bay Area, one-bedroom DADUs (600-800 sqft) typically rent for $2,500-$4,000 per month.

The cost is steep. You are looking at $250K minimum for a modest unit, and $500K or more for a larger build with higher-end finishes. But factor in rental income over 10 years ($300,000-$480,000 gross) plus the boost to your property’s appraised value, and the ROI picture changes fast.

DADUs also score highest on appraisals. Because they are independent structures with their own foundation and utilities, appraisers treat them more like separate homes than additions. That matters when you refinance or sell.

One more consideration: AB 1033 allows California cities to opt in to letting homeowners sell their detached ADU as a separate condo unit. As of 2026, a handful of cities, including San Jose, San Diego, and Santa Monica, have adopted enabling ordinances. If your city opts in, your DADU could become a sellable asset on its own.

What Does AADU Stand For?

AADU stands for Attached Accessory Dwelling Unit. This is a unit that physically connects to your existing house. It shares at least one wall with the primary residence but has its own entrance, kitchen, and bathroom.

AADU Specs at a Glance

• Size: Up to 1,200 sqft or 50% of the primary home’s floor area, whichever is less
• Structure: Shares a wall with the main house
• Utilities: Can often share water, sewer, and electrical connections, saving $15,000-$30,000 compared to a DADU
• Cost: $150,000-$350,000 in the Bay Area
• Owner-occupancy: Not required
• Timeline: 6-10 months

When an AADU Is the Right Call

AADUs work best on smaller lots where a detached structure would not fit within setback requirements or would eat up your entire yard. The shared wall cuts construction costs because you skip one exterior wall entirely, and utility routing is simpler since you are tying into existing lines rather than trenching new ones.

The trade-off is privacy. Shared walls mean shared noise. Tenants and homeowners are closer together, which typically means lower rental income: $2,000-$3,000 per month for a one-bedroom in the Bay Area, versus $2,500-$4,000 for a comparable DADU.

AADUs are especially popular for family housing. If your aging parent or adult child needs their own space but you want them close, an attached unit gives them independence while keeping you steps apart. No crossing the yard in bad weather. No separate structure to maintain.

For a side-by-side breakdown of these two options, see our detached vs. attached ADU guide.

Garage Conversion ADU: The Fastest Path to a Full-Size Unit

A garage conversion transforms your existing attached or detached garage into a livable ADU. You are repurposing a structure that is already standing instead of building new.

Garage Conversion Specs at a Glance

• Size: Limited by your existing garage footprint (typically 400-500 sqft for a two-car garage)
• Structure: Uses the existing garage shell; the garage door is replaced with a wall, window, or French doors
• Utilities: Can often tie into the main house’s connections
• Cost: Starting at $120,000 in the Bay Area
• Parking: California state law eliminated parking replacement requirements for ADU garage conversions
• Timeline: 4-6 months

When a Garage Conversion Is the Right Call

Speed and affordability. The foundation and framing already exist, so you skip the two most expensive phases of construction. A garage conversion gets you a full ADU with its own kitchen and bathroom for roughly half the cost of a detached unit.

The limitations are real. Your size is locked to the existing garage footprint. Ceiling height is typically 8 feet, which is workable but not spacious. And you lose your enclosed parking (though the law protects you from replacement parking requirements).

Garage conversions are also the simplest ADU type from a permitting standpoint. Because you are working within an existing structure, there are fewer engineering unknowns and fewer things for a plan checker to flag.

For cost and ROI details, see our garage conversion vs. detached ADU comparison.

Difference Between ADU and JADU in California

This is one of the most common questions homeowners ask. A JADU (Junior Accessory Dwelling Unit) is fundamentally different from every other ADU type. It is not a new structure. It is not even a conversion of an outbuilding. A JADU is a unit of no more than 500 square feet contained entirely within an existing single-family residence.

You create a JADU by converting interior space, like a spare bedroom, a section of your home, or part of an attached garage, into an independent living area. The result is a compact studio or one-bedroom within your existing walls.

For a complete breakdown, see our JADU vs. full ADU comparison.

JADU Specs at a Glance

• Size: 500 sqft maximum
• Location: Must be entirely within the existing single-family home or attached structure
• Kitchen: An efficiency kitchen is permitted (sink, counter space, small appliances; a full range is not required)
• Bathroom: Can have its own or share one with the main house
• Utilities: Shares all utilities with the main house; local agencies cannot charge connection fees
• Cost: $40,000-$80,000
• Owner-occupancy: Under AB 1154 (effective January 2026), only required when the JADU shares a bathroom with the main house. If the JADU has its own bathroom, no owner-occupancy requirement applies.
• Timeline: 2-4 months

When a JADU Is the Right Call

Budget is the biggest reason. At $40,000-$80,000, a JADU is the only ADU type that comes in under $100K. All the work is interior, so you avoid the costs of a new foundation, exterior walls, roofing, and utility trenching. And with a 2-4 month timeline, rental income starts flowing faster than with any other option.

The limitations are size and amenities. At 500 sqft max with an efficiency kitchen, a JADU is best suited for a studio or small one-bedroom layout. Bay Area rents run lower: $1,200-$2,000 per month. But on a per-dollar-invested basis, JADUs often deliver the fastest payback.

One strategy we see frequently: build the JADU first (2-4 months, $40K-$80K), start collecting rent, then use that income to help finance a DADU in the backyard. California allows one JADU plus one full ADU on a single-family lot, so you can end up with two income-producing units on one property.

Is a DADU the Same as an ADU?

No. This is the most common point of confusion in the “DADU vs ADU” search.

ADU is the category. DADU is one item in that category. Every DADU is an ADU, but not every ADU is a DADU. An attached ADU shares a wall with your home. A garage conversion repurposes existing space. A JADU sits inside your house. Only a DADU is a fully detached, standalone structure.

The confusion comes from the fact that some people use “ADU” casually to mean a detached backyard unit. Technically, that is a DADU. If someone says “I’m building an ADU,” you need to ask follow-up questions to know which type they mean.

Difference Between ADU and DADU: The Three Key Distinctions

If you are comparing a standard attached ADU (AADU) to a detached ADU (DADU), three things separate them.

1. Structure and placement. An AADU shares a wall with your home. A DADU is a standalone building on your lot with air space between it and the main house.

2. Utility connections. AADUs can tie into your home’s existing water, sewer, and electrical lines. DADUs need their own independent connections, which adds $15,000-$30,000 to the project.

3. Privacy and rental income. DADUs provide full separation between the homeowner and the tenant or family member. That privacy commands higher rent. In the Bay Area, the gap is roughly $500-$1,000 per month more for a detached unit versus an attached one of similar size.

Can I Build a JADU and an ADU on the Same Property?

Yes. California law explicitly allows one JADU plus one full-size ADU on any single-family lot. The JADU must be within your existing home or attached garage. The full ADU can be detached, attached, or a garage conversion.

This “JADU + ADU” combination is one of the most effective strategies for maximizing rental income from a single-family property. Two units, two income streams, one lot.

The rules are clear about what qualifies for each slot:

• The JADU slot: One unit, 500 sqft max, within existing walls, efficiency kitchen allowed.
• The full ADU slot: One unit, up to 1,200 sqft, can be DADU, AADU, or garage conversion, must have full kitchen and bathroom.

You cannot build two full ADUs on a single-family lot (multifamily lots have different rules). But you can build one of each.

Which ADU Type Is Cheapest to Build?

Ranked from least to most expensive in the Bay Area:

1. JADU: $40,000-$80,000. Interior conversion only. No foundation, no exterior walls, no utility trenching.
2. Garage conversion: From $120,000. Uses existing structure. Foundation and framing costs eliminated.
3. AADU (Attached): $150,000-$350,000. New construction, but shared wall and shared utilities reduce scope.
4. DADU (Detached): $250,000-$500,000+. Ground-up build with independent utility connections.

The price differences are driven by construction scope. A JADU remodels existing interior space. A garage conversion works within an existing shell. An AADU adds onto an existing structure. A DADU builds from scratch. Each step up adds foundation work, framing, roofing, and utility infrastructure.

For city-by-city pricing across the Bay Area, see our ADU cost guide.

Do All ADU Types Need Separate Utility Connections?

No. This is one of the biggest cost variables between ADU types.

JADUs share all utilities with the main house. California law prohibits local agencies from charging utility connection fees for JADUs. This is one reason they are so affordable.

Attached ADUs and garage conversions can usually tie into your home’s existing water, sewer, and electrical lines. Some municipalities may require a separate electrical meter, but the physical connections are shared.

Detached ADUs (DADUs) almost always require new, independent utility connections. You are running separate water, sewer, and electrical lines from the street or the property’s main connections to a standalone structure. This adds $15,000-$30,000 to the project, depending on the distance between the DADU and the connection points.

Utility costs are one of the main reasons attached ADUs are $100K-$150K cheaper than detached ones, even at similar square footage.

Which ADU Type Adds the Most Property Value?

Detached ADUs (DADUs) add the most appraised value. Because they are independent structures with their own foundation, roof, entrance, and utility connections, appraisers treat them more like separate residences than like room additions.

Attached ADUs and garage conversions add value too, but they are typically assessed as additional livable square footage on the primary home rather than as independent units. The distinction matters because a second “dwelling” on the property is worth more per square foot than additional rooms in the main house.

JADUs add the least appraised value in absolute terms because they are small and contained within the existing home. But on a return-on-investment basis, they can perform well because the initial cost is so low.

Can I Sell My ADU Separately From My House?

Under AB 1033 (effective January 1, 2024), California cities can opt in to allow homeowners to sell a detached ADU as a separate condominium unit. This is not an automatic right. Your city must adopt an enabling ordinance.

As of 2026, a small number of cities have done so. San Jose was the first and has completed its initial ADU-to-condo conversions. San Diego, Santa Monica, Berkeley, and San Francisco have also taken steps toward adoption.

The process involves a formal condo conversion: surveying, civil engineering, legal documentation, and creation of a homeowners association. It is not quick or cheap. But for DADU owners in participating cities, it opens a path to selling the unit independently.

This is another reason DADUs hold a unique position among ADU types. They are the only type eligible for separate sale under AB 1033, because attached ADUs and JADUs share structure or utilities with the primary home.

Head-to-Head: Which ADU Type Fits Your Situation?

For Maximum Rental Income: Build a DADU

A detached ADU generates the most monthly rent. Tenants pay a premium for a freestanding unit with full privacy. In the Bay Area, a one-bedroom DADU rents for $2,500-$4,000 per month. Over 10 years, that is $300,000-$480,000 in gross rental income.

The upfront cost is highest ($250K-$500K+). But the combination of rental income and property value increase makes DADUs the strongest long-term investment for homeowners who can afford the build.

For Multigenerational Living: Build an AADU or JADU

When a family member needs their own space but proximity matters, an attached ADU or JADU is the better fit. The shared wall (AADU) or shared home (JADU) keeps everyone close. An aging parent can maintain independence while being steps away. An adult child gets privacy without leaving the property.

If your family member needs a full kitchen and dedicated bathroom, go with an AADU. If a compact efficiency kitchen and potentially shared bathroom work, a JADU saves significant money.

For a Home Office or Creative Studio: DADU or Garage Conversion

Working from home in a separate structure eliminates the distractions of the main house. A small DADU (400-500 sqft) or garage conversion gives you a dedicated workspace with its own entrance, climate control, and sound separation.

A garage conversion is the faster, more affordable route if you have a garage you are willing to give up. A DADU gives you more design control and preserves your parking.

For the Tightest Budget: Build a JADU

At $40,000-$80,000, a JADU is the only ADU type under $100K. If budget is the primary constraint and you have interior space to convert, a JADU delivers a functional independent unit for a fraction of what other types cost. The 2-4 month timeline means you are collecting income (or housing a family member) faster than any other path.

For Two Units on One Lot: JADU First, DADU Later

Build the JADU first. It takes 2-4 months and costs $40K-$80K. Start collecting rent. Then plan your DADU, using that rental income to help finance the larger project. California allows one JADU plus one full ADU on a single-family lot, so this combination is fully legal and increasingly popular.

How to Choose: Budget, Property, and Goals

By Budget

• Under $100K: JADU is your only option at this price point ($40,000-$80,000)
• $120K-$200K: Garage conversion fits this range well (from $120,000)
• $150K-$350K: Attached ADU gives you a full-size unit connected to your home
• $250K and above: Detached ADU provides maximum space, privacy, and rental potential

By Property

• Large backyard with setback clearance: A DADU takes full advantage of your outdoor space
• Smaller lot or tight setbacks: An AADU or JADU works within or alongside your existing footprint
• Underused two-car garage: A garage conversion is the most efficient use of what you already have
• Spare bedrooms or unused interior space: A JADU converts what is already there

By Goal

Goal	Best ADU Type	Why
Highest rental income	DADU	Privacy commands premium rents ($2,500-$4,000/mo)
Fastest rental income	JADU	2-4 month timeline, lowest cost
Family housing (aging parent)	AADU or JADU	Proximity to main home
Home office	DADU or garage conversion	Sound separation, dedicated space
Maximum property value	DADU	Appraised as independent structure
Two units on one lot	JADU + DADU	California allows one of each
Sellable separate unit	DADU	Only type eligible under AB 1033

California ADU Rules That Apply to All Types

California has steadily removed barriers to ADU construction over the past decade. Here are the rules that apply across every type:

• Permit timeline: Cities must act on a complete ADU application within 60 days
• No public hearing required: ADUs are approved ministerially if they meet standards
• Setbacks (detached): Four feet from rear and side property lines
• Parking: No additional parking required for new ADUs. No replacement parking required for garage conversions.
• Owner-occupancy (full ADUs): Not required for detached, attached, or garage conversion ADUs (AB 976 made this permanent as of January 1, 2024)
• Owner-occupancy (JADUs): Required only when the JADU shares a bathroom with the main house (AB 1154, effective January 2026)
• Combining units: One JADU plus one full ADU allowed on a single-family lot
• Impact fees: ADUs and JADUs under 750 sqft are exempt from impact fees

For a full overview of current legislation, see our California ADU laws guide. For Bay Area pricing by city, see our ADU cost guide.

How Custom Home Builds Every ADU Type

Custom Home has been designing and building ADUs across the Bay Area since 2005 (CSLB #986048). We build all four types: DADUs, AADUs, JADUs, and garage conversions, with over 100 projects completed.

Our two-phase process works the same regardless of ADU type. In Phase 1 (Design), we assess your property, evaluate which type fits your goals and lot constraints, and create detailed plans with 3D visualizations and line-by-line pricing. In Phase 2 (Build), we handle permitting, construction, and inspections with locked-in pricing. No surprises.

The right ADU type depends on your specific property. Lot size, setback clearance, existing structures, utility access, and local zoning all factor into the recommendation. A site assessment is the best way to determine which option delivers the most value for your situation.

Start Your ADU Project

Ready to figure out which ADU type fits your property? Contact Custom Home for a free consultation or learn more about our ADU design and build services.

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ADU regulations and costs change frequently. Information in this guide reflects California law as of early 2026 and Bay Area pricing ranges based on our project experience. Contact us or your local planning department for the most current requirements and cost estimates for your specific property.