Key Points

ADU meaning refers to an Accessory Dwelling Unit, a secondary, fully independent living space built on the same property as a primary home.
ADUs come in multiple forms, including detached units, attached additions, garage conversions, above-garage suites, and basement conversions.
Building an ADU offers major benefits like flexible living space, rental income potential, multigenerational housing support, and increased property value.
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ADU: The Meaning Behind the Acronym

Ever feel like your home is almost big enough—if only you had one more flexible space?

Or catch yourself wondering how other Tucson homeowners are creating guest suites, rental units, and home offices without leaving their existing property?

In this guide, you’ll learn exactly what ADU meaning refers to, the different types of accessory dwelling units, and the pros and cons of building one on your property.

By the end, you’ll know how an ADU can increase your home’s value, give your family more breathing room, and open the door to brand-new lifestyle possibilities.

If you’re curious whether an ADU could be the perfect fit for your home, reach out to the ADU pros at Frei Remodel and Design by giving us a call or sending a quick message through our contact form.

We’re here to help you explore what’s possible.

What Is an ADU?

ADU stands for accessory dwelling unit ADU, which is a supporting housing structure on the same lot as a standard home that has its own kitchen, bathroom facilities, living space, and sleeping area.

Other names for ADUs include an in-law suite, granny flats, a backyard cottage, a guest house, a casita, and a carriage house.

These accessory units come in different forms.

However, it is not a full secondary residential unit if it doesn’t provide complete living facilities independent of the main house.

Therefore, a standard ADU must include a kitchen, dining/living room, bedroom, and bathroom.

The Different Types of Accessory Dwelling Units

Single-car garage, converted to an ADU, with a closed white door, red brick and white siding exterior, surrounded by green shrubs and trees, and a concrete driveway in front. - ADU meaning

There are five main types of accessory dwelling units. They include the following:

  1. Detached new construction ADUs. These detached ADUs stand alone as accessory dwelling units on your property and are completely separate from the main house, often with a separate entrance and separate utilities that give users more privacy. In Arizona, ADUs are also known as casitas.
  2. Attached ADUs. The attached ADUs are a home addition extending from the existing primary residence. They are ideal when there isn’t enough space for a fully detached unit.
  3. Above-garage ADUs. These secondary units occupy the space above a garage or detached garage.
  4. Garage conversion ADUs. These accessory dwellings occupy the entire garage space, unlike the upper part of the garage, as seen in the above-garage units, making this type of garage conversion a popular choice when you do not require as much parking.
  5. Basement conversion ADU. Basement conversion ADUs turn the lower level into a complete basement apartment, typically with a separate entrance.

Along with these types come ADU design ideas to help them fit your style.

Before settling on the type of ADU to construct for your home, you need to evaluate the local rules in your area.

  • For example, in Tucson, AZ, your ADU cannot be bigger than 10% of the lot size (a maximum of 1,000 square feet).
  • The maximum height must be 12′ or match the height of the primary structure if you live in a home with two floors.

In our experience, we’ve noticed that queries around “ADU meaning” stem from confusion about the property dimensions.

The Advantages of ADUs or Backyard Cottages

A light blue ADU with white doors - ADU meaning

ADUs or backyard cottages are beneficial in the following ways:

  • They are income-generating assets. A fully-fitted ADU is an additional source of income for homeowners who rent them out. The extra income can go toward paying off the mortgage on the lot.
  • They increase the population of an area. ADUs increase the number of occupants on a lot. In a sparsely populated neighborhood with no more empty lots to build on, ADUs are a great way to bring more residents to the area.
  • They keep families closer. Senior citizens can choose to move into ADUs to stay close to their loved ones and caregivers. Younger families may decide to live in an ADU at home until they qualify for a separate mortgage.
  • They are great for downsizing. Senior citizens can elect to move to an ADU and rent out the primary unit.
  • They are a perfect option for a home office. With remote work more popular than ever, ADUs give you a proper office away from the main living areas.

The Disadvantages of Accessory Dwelling Units

ADUs are not without their disadvantages.

Some of them include the following:

  • They require as much attention as a traditional single-family home. An ADU is essentially another home, so you must pay attention to permits, building codes, and more.
  • Building an ADU is expensive. Sometimes, it costs as much as a brand-new traditional home in other places. You’ll also have to pay higher property taxes and higher utility bills.
  • ADUs require maintenance. If you use the property for rentals, you must keep it in shape.
  • ADUs take up usable square footage. Building a detached or attached ADU will make your outdoor living space much smaller overall.
A guest house ADU with white vertical siding - ADU meaning

Do I Need an Accessory Dwelling Unit?

The decision to build an ADU comes down to your personal needs.

Do you have a genuine desire to give your family a little extra room?

Do you want to move your loved ones closer?

Will a little more income as a landlord move the needle for your financial situation?

After answering these questions, the next step is to research the regulations surrounding ADUs in your area to avoid breaking any codes.

How Much Does Building an ADU Cost?

The cost of building an ADU varies as widely as the cost of building a traditional home.

Detached units will cost more than those attached to the existing structure.

Additionally, your choice of furnishings, fittings, materials, and the number of contractors required for the project will significantly influence the final cost.

You can expect to spend anywhere between $3,500 and $300,000 for an ADU.

As a result, they are not always the affordable housing units many say they are.

Will an ADU Improve the Value of Your Home?

ADUs can increase the value of a property.

However, it isn’t easy to quantify the value they can bring.

Property owners only find out the value of the ADU when it’s time to sell the property.

Away from the financial aspects, you should consider other ways an ADU can bring value to your home.

For example, an elderly family member living in an ADU may enjoy the feeling of living next to loved ones instead of in an assisted living facility. 

Can I Build an ADU as a DIY Project?

Unless you are a qualified professional in the several contractor areas required to complete a home, you can’t build an ADU as a DIY project.

Apart from erecting the structure, you need plumbing, heating and cooling, electricity, interior decoration, and more.

Taking on projects in these areas without the qualification will lead to legal troubles.

Ready to Build Your ADU? Frei Remodel and Design Can Make It Happen

Now that you understand the real ADU meaning, you’ve seen how these compact living spaces can boost flexibility, create rental income, support family needs, and make better use of the property you already own.

You also learned the different forms an ADU can take and the key factors to consider before choosing the right one for your home.

If you’re excited to bring an ADU to life, Frei Remodel and Design can handle everything from design to permits to full construction.

Our ADU contractors are ready to turn your backyard casita, rental unit, or guest suite into a beautiful and functional space, so reach out when you’re ready to get started.

Frequently Asked Questions

Are ADUs legal in Arizona?

Yes. ADUs are legal in Arizona, and many cities, including Tucson, have adopted ordinances that allow homeowners to build them. Cities set their own rules for size, setbacks, and placement. For example, Tucson allows one ADU per residential lot, up to 1,000 square feet or 10 percent of the lot size, along with specific height and design requirements.

How much does an ADU permit cost in Arizona?

Permit fees vary by city because each municipality sets its own rates. In most Arizona cities, including Tucson, homeowners can expect permit fees to range from a few hundred dollars to several thousand dollars depending on the project size, plan review complexity, and utility connections. The exact cost is determined during the permitting process after plans are submitted.

What is the meaning of ADU?

ADU stands for Accessory Dwelling Unit, which refers to a secondary housing unit located on the same property as a primary single-family home. An ADU must include its own kitchen, bathroom, living space, and sleeping area, making it a fully independent residential unit.

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