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JADU vs ADU - 7 Key Differences

ADUs, or accessory dwelling units, are a great way to add living space and boost property value, but what if you don’t have much room to work with? That’s where Junior ADUs (JADUs) come in. JADUs are great for maximizing small spaces and can be cheaper to build.
Updated Aug 08, 2023
JADUs range between 150 sq. ft and 500 sq. ft and don’t need full-sized kitchens or their own bathrooms – the biggest space saver – while standard ADUs can be larger, up to 1,200 sq. ft. Both options can bring families closer and open up new avenues for passive income, and recent regulatory changes and fee waivers have made them more accessible and affordable.
This guide takes a closer look at how a JADU is different from an ADU, the potential benefits of both, and how to decide if an ADU or a JADU is the best option for your home.
First, let’s understand what a JADU is and how it differs from an ADU.

What is a JADU?

A JADU is a smaller ADU, and this is what sets it the most apart from a standard ADU. JADUs are under 500 sq. ft. and either attached to or contained entirely within the existing home. They can be created by converting an underutilized space, such as a basement or a garage, or building an attached area, and are an affordable and compact alternative to regular-sized ADUs.
Let's explore the differences between JADUs and ADUs in more detail.

7 Key differences between an ADU and JADU

Here’s a quick look at the specific ways JADUs and ADUs differ in terms of their facilities and legal requirements:

1. Size

The size requirements for ADUs and JADUs vary depending on the location. In popular cities such as Los Angeles, San Diego, San Francisco, and Seattle, the minimum JADU size is 150 sq. ft. and the maximum size is 500 sq. ft. For ADUs, the size requirements may differ depending on the available space on your property.

2. Cost

The cost of building an ADU or JADU can vary depending on several factors, including location, size, design, and finishes. In California and most other areas in the US, the cost of an ADU can range from $200,000-$400,000. In contrast, a JADU can cost significantly less ($50,000-$90,000) due to its smaller size because it doesn’t need a bathroom or full kitchen, and the potential for converting existing space instead of ground-up construction.

3. Entrance

Standard ADUs require separate entrances, providing occupants with complete privacy and independence from the primary home. While JADUs also need a separate entrance, if they share a bathroom with the main home, they are required to have an entrance to the primary unit as well.

4. Parking

Parking requirements for ADUs and JADUs may vary depending on your local regulations. If your ADU is located in a coastal zone or a sustainable development zone, you may need to provide an additional parking space. You may not need one if your ADU is within walking distance of public transport.
JADUs in California don’t require additional parking spaces and in Seattle, both ADUs and JADUs don’t require them.
Navigating local regulations can be tricky, but the right provider will make sure your ADU project is compliant at every stage so you don’t face any regulatory hiccups along the way.

5. Utilities and power appliances

ADUs and JADUs require essential utilities such as electricity, water, and gas, but JADUs can share existing utility services attached to the primary home. This offers a significant cost benefit because you’re saving on costly plumbing and electrical work.

6. Bathroom and kitchen requirements

Because JADUs are contained entirely within the primary home, they don’t need their own bathroom and can share one with the primary home. ADUs must be equipped with a bathroom.
ADUs require their own kitchen with facilities for cooking, food preparation, running water, and cabinetry. JADUs require basic cooking facilities and need an “efficiency kitchen” – that contains a food preparation counter, storage cabinets, and appliances that require no more than 120V – at the very least.
When planning to build an ADU or JADU, it’s important to be aware of the legal requirements relevant to your local jurisdictions. Let's explore a few popular areas in the US:
Renting: Short-term rentals aren’t allowed for ADUs or JADUs. The minimum rental period is 30 days.
Owner Occupancy: Owner occupancy of the primary residence isn’t required for ADUs but is required for JADUs.
Individual sale: Not allowed for ADUs or JADUs.
Renting: Short-term rentals aren’t allowed for ADUs or JADUs. The minimum rental period is 30 days.
Owner Occupancy: Owner occupancy of the primary residence isn’t required unless the property has both an ADU and a JADU. Owner occupancy of the primary residence is required for JADUs.
Individual sale: Not allowed for both ADUs and JADUs.
Renting: Short-term rentals aren’t allowed for ADUs or JADUs. The minimum rental period is 30 days.
Owner Occupancy: Owner occupancy of the primary residence isn’t required for ADUs but is required for JADUs.
Individual sale: Not allowed for both ADUs and JADUs.
Renting: ADUs can be rented short-term, with a license. Because JADUs aren’t considered separate units, and they may be rented under different requirements.
Owner Occupancy: Not required for ADUs but required for JADUs.
Individual sale: ADUs, especially DADUs, can be sold separately under specific requirements, such as if the lot is owned by a condo association. JADUs may not be sold separately.
In California, the government can impose restrictions on ADUs if necessary for fire and life safety. JADUs are held to the same local regulations as the primary unit, so if the primary unit requires a fire sprinkler system, then the JADU requires one as well.
Seattle-based ADUs and JADUs must meet the current building standards and codes of regular homes.
Take a closer look at the legal requirements for ADUs in these specific areas:
With the recent regulatory updates made across the US, you can now apply for an ADU or JADU online through the website of your local authority. These permits are typically approved or denied within 60 days for LA-based projects and in approximately four months for Seattle-based projects. Keep in mind that regulations change, so always consult authorities and review compliance with the legal requirements in your area when applying.

JADU vs. ADU - Which one is right for you?

Depending on what you want to use your second space for, you might benefit more from either an ADU or a JADU. Some areas do allow you to build both on your property, but if you have to choose one, here are a few factors to keep in mind.

Who should build a JADU?

JADUs are smaller and can cost less than standard ADUs, so they’re perfect for homeowners who have 150 - 500 sq. ft. to work with and are looking to keep costs down.
JADUs can be internally connected to the primary home and share sanitation facilities, so they are a great way to house older children who want independence but aren’t yet ready to move out.
Overall, JADUs are an affordable alternative to traditional homes amid the current housing crisis, but there are some benefits to building an ADU instead.

Who should build an ADU?

For homeowners looking to maximize their property value, an ADU is the way to go. ADUs, especially detached ADUs, can bring in the most in terms of rent and significantly add to your home’s resale value.
ADUs are completely independent of the primary home. Attached ADUs may share a wall but cannot be internally connected and must have a separate entrance. Because of this, ADUs are more private than JADUs and are incredibly versatile. Whether for aging-in-place or renting out, an ADU is a great addition to your home.
Consulting with an ADU expert before you get started is the best way to get the most out of your project. An ADU expert can help you navigate the entire process, from design to construction, budgeting, financing, timelines, and permitting.
While JADUs are a fast and easy solution to add extra living space within your property, they may not suit every homeowner's needs. Let’s take a look at the limitations of having a JADU and if an ADU would be a better fit for your preferences.

What are the limitations of a JADU?

Some aspects of JADUs can be beneficial but also limiting in comparison to standard-sized ADUs.
JADUs are smaller than ADUs, and may not be suitable for homeowners looking for more spacious and private living, while ADUs offer independent access and the flexibility to customize it according to your needs.
JADUs are only allowed within single-family homes, so if you’re a multi-family homeowner, a standard ADU is your only option. ADUs, especially detached ADUs, can bring in the most rental income, as renters are usually willing to pay more for the privacy, flexibility, and independence they offer.

To sum up

Both JADUs and standard ADUs come with their own benefits, but the right provider can help you make the right choice and create an ADU that suits your needs.
Cottage specializes in custom ADUs and partners with a trusted network of contractors to bring detached, attached, conversion, and JADUs to life. Book a consultation with one of our specialists, or check out some of our projects for inspiration.


1. Can I have an ADU and JADU in California?

Yes. If you own a single-family home in California, you can have both an ADU and a JADU on your property. The legislation allows homeowners to construct one ADU, whether attached or detached from the main residence, along with a JADU. This means you can have two separate living units on your property and utilize unused space. Note that regulations and policies may vary depending on local zoning codes, so consult with local authorities to ensure compliance before planning.

2. Can I build an ADU or JADU on my property in Washington State?

Yes, and depending on the zoning regulations, you may construct two ADUs on your lot. Review and comply with local zoning codes and regulations to ensure your property is eligible to construct ADUs.

3. What is the maximum ADU size in Seattle?

In Seattle, the maximum size for an ADU depends on the zoning. In neighborhood residential zones, including RSL (Residential Small Lot) zones, the maximum size for an attached ADU or a detached ADU is 1,000 sq. ft. In low-rise zones, the maximum size is 650 sq. ft. ADUs must comply with Seattle codes, including those related to residential, building, mechanical, electrical, energy, land use, environmentally critical areas, and shoreline codes.

4. Can a JADU be converted from a detached garage?

No, only attached structures may be converted into JADUs. You can still convert a detached garage into a detached ADU.

5. What is the smallest ADU allowed?

JADUs, or junior ADUs, are the smallest type of ADUs allowed and can be between 150 and 500 sq. ft. Standard ADUs in California can be up to 1,200 sq. ft. and their size requirements usually depend on the size of the existing home.

6. Can a JADU have a full kitchen?

Yes, a JADU can have a full kitchen but it may be difficult to accommodate one with the 500 sq. ft. limit. JADUs only need basic cooking facilities, so a kitchenette is enough.

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