What Is An ADU And Why Should I Have One?

What is an ADU? An accessory dwelling unit is what ADU stands for. Accessory dwelling units offer an affordable alternative to standard housing. The units serve more than one purpose, with one of those purposes being housing. 

What Is An ADU

A 2019 study from the Terner Center on Housing Innovation noted that one unit of affordable housing in San Francisco, California costs about $450,000. ADUs and JADUs can often be built at a fraction of that price. And to make it cheaper, homeowners are allowed to use existing lots to create additional housing, without being required to provide extra infrastructure.

What Is An ADU?

ADU stands for Accessory Dwelling Unit. The structure is used for living purposes and other reasons. ADUs are between 800 and 1,000 square feet.

They are most often used for hobbies, guests, and add-ons for that extra room that you need yet don’t have space for in your main house. But there are more reasons to have an ADU than to not have an ADU. 

History Of The Accessory Dwelling Unit

History Of The Accessory Dwelling Unit

The first ADUs appeared after World War II when an increased population in certain countries paired with the rise in poverty supplied the demand. The 1950s and 1960s probably saw the largest number of ADUs.

Between the end of the war and 1960, San Francisco alone had over 20,000 ADUs, almost all of them built illegally. 

By the 70s, permits were required to build ADUs in particular and laws were put in place to avoid their construction. Not many of them held up and the construction of them didn’t slow down until the 90s.  

ADU Styles

Let’s look at the different ADU styles that you’ll find on most single-family properties.

Types Of ADU
Flavin Architects

It may not seem important to learn the ADU styles, but they affect the required codes and permits. 

Detached ADU

These granny pods are detached from the home. They require the most permits and have the most regulations. So, build these with care and educate yourself on what you need to build them.

Attached ADU

Attached ADUs are attached to your home but built for the purpose of an ADU. They are add-ons to your home and work just like any other add-on. They are registered as additions rather than separate ADUs.

Above Garage ADU

You can build on top of your existing garage but the steps you go through will depend on whether your garage is attached or not. To your home that is. This is a great way to save space and add a lot more room.

Garage ADU

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Right Arm Construction

If you have the garage space and don’t want to use it as a garage, you can transform it into an ADU. This is usually quite easy and doesn’t require as many steps as long as you are allowed to build in your area.

Basement ADU

Basement ADUs are probably your best bet if you want to get around codes and laws. Because the basement is inside of your home, you can convert it any way you like and probably won’t need a permit.

There are a few states where you have to get a permit to do any type of construction inside of your home. So check with that first. Other than that, you should be good to go and won’t pay any extra taxes for it.

Uses For An ADU

Uses For An ADU
Northwest Heritage Renovations

ADUs were popular in the 60s. It was then when the detached units were called backyard cottages.

Today, and due to housing demand, ADUs are becoming popular home extension projects. You should make sure you don’t need a permit to use an ADU for any of these before you build them. 

Granny Flat

A granny pod is one of the most popular uses for ADUs. In fact, it is considered the original use. Because granny pods were used for in-laws to stay in whenever they couldn’t stay alone or wanted to be close to family. 

In some cultures, like the Amish culture, it is the standard for in-laws to stay in what is called a “dawdi haus” which is a building where parents or grandparents live. This can be seen in many, many cultures. 

Hobby Room

There is hardly a better place for a hobby room than an ADU. Having a separate area for your hobby can feel freeing and homey. Not to mention, it lets you stay organized with a place to put all of your stuff.

The hobby you have doesn’t matter. It can be sewing, crafts, sculpting, or something else entirely. The point is to create a space for you to let your creativity flow freely and uninterrupted. 

Home Gym

Every house needs a home gym. Because there’s not much better you can do for yourself than get healthy and in shape. You can create a home gym with a small ADU and that is all you need for your workout essentials. 

You don’t have to have a full-on public gym with everything anyone could ask for. All you really need is a small area where you can have the equipment that you and you alone will use on a regular basis.

Guest House

This is another super common use for an ADU. You can use an accessory dwelling unit for your guest room. It gives guests someplace private to stay whenever they are around, even with their own kitchenette if you see fit.

Alternatively, you can use the guest house like a pool house if you have a pool. It can work as both, using it as a pool house when you don’t have any guests and a guest house when you do. That way it is always in use. 

Man Cave Or She Shed

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GemBuilt Construction & Remodeling

Thinking of an ADU as a piece of fresh clay. You can mold its purpose however you please. Turn your ADU into a man cave or she-shed. If you need a space that offers an escape, and ADU would be ideal or any family member. 

Use your man cave ADU as a place where you take naps or read. If you’ve been wanting to write that novel, an ADU provide a quiet space where you could write uninterrupted whenever you want.

Game Room

An ADU would make a nice game room. You could also turn it into a VR room. If you have a larger space you can make an incredible VR room that will give you the freedom to really immerse yourself.

Instead of a VR room, use the space as a family game room. You could host family game night once a week.


Need a safe place for the kids to get away and have some fun? You can use a playhouse that looks any way that you want by converting an ADU into one. This can work for indoor or outdoor play in any season.

If it is extra hot, you can install an AC so they can stay cool no matter how hot it is outside. Provide a mini-fridge if you want to offer refreshments and cool water for them too. Make it as comfortable as possible. 

What Is A Junior Accessory Dwelling Unit (JADU)?

A junior accessory dwelling unit (JADU) is the little brother to the ADU. Here are the standard specifications of a JADU. 

  • Size – a maximum of 500 square feet
  • Ingress and egress – allow 150 square feet
  • Location – must be within a proposed or existing single-family dwelling or accessory structure. 
  • Separate Entrance – Exterior access is required from the proposed or existing single-family dwelling.
  • Parking Not Required – JADUs do not require a parking space.
  • Bathroom – May have a separate bathroom or shared with the single-family dwelling.
  • Kitchen – Must meet “Efficiency Kitchen” requirements. Cooking facilities with appliances that use 240-volt outlets are permitted

ADU Building Codes

Not every home can have an ADU or JADU. Land and property ownership must adhere to local jurisdictions regarding property. Similar to A-frame house ownership, just because you’re a property owner doesn’t mean you can add a stand-alone unit to your existing home whenever you want.   

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Mighty Buildings

Zoning Regulations

ADUs proposed to a subdivision committee in residential areas must be considered in any residential or mixed-use zone. For other ADUs, local governments may, by ordinance, designate areas in zones where residential uses are permitted that will also permit ADUs.

However, any limits on where ADUs are permitted may only be based on the adequacy of water and sewer service, and the impacts on traffic flow and public safety. Further, local governments may not preclude the creation of ADUs.

Ordinances And Covenants

When you propose a detached ADU living space, you’ll need to determine if it complies with local ordinances and covenants.

Your zone might be approved to build a certain type of structure, but a local ordinance restricts the size or height of that structure.

In California, there isn’t a minimum lot size requirement for ADUs. However, local governments may enforce building and health and safety standards. They could also consider design, landscape, and other standards to facilitate compatibility.

HOA Jurisdiction

Another caveat of ADUs and JADUs is how your local homeowners association (HOA) cannot prevent you from building them. Covenants, conditions, and restrictions (CC&Rs) that prohibit ADUs or JADUs cannot be enforced.

Frequently Asked Questions (FAQ)FAQ

What Is An ADU In Real Estate?

ADUs in real estate are “additional living quarters on single-family lots that are independent of the primary dwelling unit.” If you don’t have another house on the property, then you don’t have an ADU.

Are ADUs Appraised?

ADUs can be appraised.  They are appraised in the way that an outbuilding or guest house is appraised rather than the way that the home on the property is appraised. They can raise property value by 30%.

What Is A CoC For An ADU?

A Certificate of Compliance or CoC is a formal certification stating that the owner of the ADU has met a set of conditions. The certificate comes in handy when selling the ADU or using it for business purposes.

What Is The Maximum Size Of An ADU?

The maximum size of an ADU depends on the region. In California, an ADU can be up to 800sqft. If it is larger than that, it may not be considered an ADU. The building can be up to 16-ft tall as well.

ADU Housing: Wrap Up

Finding ADU housing isn’t always easy. Because of the laws in place, it can feel like everything and everyone is working against you. But if you take all the appropriate steps, it can be the best decision of your life. 

The easiest way to find them is to get help. Find someone who knows the ins and outs of the area and everything that goes into getting permits and buildings things. You can even hire a contractor to do it all for you.

Extra property taxes come with ADU. Don’t let this surprise you. Learn everything you can about ADUs. 

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