Top Remodeling & Design


Accessory Dwelling Unit (ADU) 101: All The Basics You Need To Know


You may have heard of ADUs, but what are they? What can you do with them? And how does the law in your state affect whether or not you’re allowed to build an ADU?

ADUs (accessory dwelling units) are dwellings that fit into your property and provide a separate living space for someone who is usually related to the homeowner. They come in all shapes and sizes, and there’s no “one-size-fits-all” solution when it comes to building one. Here are some of the basics so that you know what you need to be thinking about before starting your project.


What Is An Accessory Dwelling Unit?

An Accessory Dwelling Unit (ADU) is an addition to the main home that provides independent living for people or another household. An ADU can be added to your existing property, but it can also stand alone as its building on the same lot as the primary dwelling unit. It’s called an “accessory” because its purpose is secondary compared to the primary residence.

  • Affordable housing for the future
  • Create extra income in your home
  • New trend that explodes property values
  • Increase in livability and longevity of senior citizens/younger generations


If you need more space for family members or tenants, want extra income through short-term rentals, or just don’t want to move out of your neighborhood when downsizing then an ADU may be right for you. As long as there are no restrictions in place by zoning laws and permits aren’t necessary, adding an ADU can be a great opportunity to increase income, maximize living space, and provide short-term lodging.

An ADU is not just an investment for future generations who are looking to build their own home one day but it’s also beneficial in the here and now! Today’s renters have different demands than those of yesteryear. With single-family homes being turned into duplexes or fourplexes, consumers are looking at shared spaces that offer more amenities within walking distance. They want easy access to public transportation, restaurants/bars/shops without having to drive everywhere they go.

  • Build an ADU for your house to increase income
  • The perfect investment- it pays you every month
  • Increase rentable space in your community
  • Save time by not having to commute everywhere


With this in mind, if you own a multi-unit property (duplex or fourplex) an ADU could be the perfect addition to your rental portfolio. It will allow you to increase rents on units that are lower than the market rate due to their age without decreasing overall occupancy levels at your other properties.

They are also known as:

  • Attic apartment
  • Backyard cottage
  • Backyard house
  • Basement apartment
  • Carriage house
  • Garage conversion
  • Garden cottage
  • Granny flat
  • Mother-in-law suite
  • Mother-in-law unit
  • Secondary dwelling unit
  • Tiny house


What Type Of Housing Is Considered Accessory Dwelling Units?

First off, let’s define what type of housing can legally become an ADU: houses with detached accessory dwellings like coach houses and garden cottages; duplexes, triplexes, townhouses; stand-alone homes such as mother-in-law suites attached garages converted into living quarters; and “detached secondary dwelling units” such as granny flats and guest houses.

You can also legally build a separate apartment building on your property, but this type of housing is not considered Accessory Dwelling Units. However, it is recommended to check with your local government before making any changes or additions to help you understand if any regulations may apply in the future.

In addition to the different types of ADUs, an “accessory dwelling unit” (ADU) means a living space for one or more persons located within a single-family home or a manufactured home that provides complete independent living facilities for those persons. An example would be converting part of your garage into additional living quarters so they have their entrance from the outside with their very own kitchen, bedroom, and bathroom. Converting your garage is not the only option, it’s one of the most popular.


What Can I Use My Accessory Dwelling Unit For?

An ADU is a great way to increase income through short-term rentals or extra space for family members. It’s also fantastic if you’re looking to downsize but still want easy access to all that city living has to offer. For example, instead of moving further away from everything into another home in the suburbs that don’t include amenities like public transportation, restaurants/bars/shops, etc. You could build a studio apartment within walking distance of where you work. This will allow you more time with friends and family when you do have “free time” and the ability to avoid long commutes.


What Is A Typical Accessory Dwelling Unit Size?

You can create an ADU in just about any home, but they are most popular in single-family homes with detached garages. The average square footage for this type of housing is usually around 500 sq ft per unit – allowing renters or family members enough space to feel comfortable. Some may even include full kitchens while others will only feature kitchenettes with mini-fridges/microwaves etc.


Regardless of what your plan looks like, keep in mind that it’s always recommended to talk over all your plans with a local building professional who specializes in creating these types of units before making any changes.


How Much Does An Accessory Dwelling Unit Cost?

This is one of the biggest questions you can get from investors because no two ADUs are created equal. While building materials may vary, you can expect that your budget will be depending on what you want to be included in your unit and how much work needs to go into creating it. Some expenses include permits/licenses, construction costs, furnishing, etc., and remember – if you’re using existing space within your home or garage for this conversion there could be structural problems so keep any potential issues in mind before doing anything.

If money isn’t an issue then feel free to dream big with whatever amenities you desire- but if you’re like the rest of us and can’t afford to spend a ton, keep in mind that quality ADUs are built on more than just size! Include high-quality finishes throughout, an open concept layout, and good storage options no matter how small it may be.


What Is Included When I Build An Accessory Dwelling Unit?

Once you’ve decided this new space will become your very own apartment or home with its very own kitchen there’s still work to do before tenants can move in. Remember, whether building from scratch or converting an existing garage/attic etc you will need permits. These legal documents outline all changes made within your property so they meet local housing standards including insulation levels required for each unit. This means that you’ll need to add things like more insulation in your attic if using it as an ADU and make sure there is enough ventilation for each unit.

  • Find out everything you’ll need to start this process
  • Start with the very basics of making sure your property is ready for tenants.
  • Get a step-by-step guide with all the necessities 
  • Learn how to avoid getting into trouble due to not having permits


When converting spaces within a single-family home, homeowners should also consider how their new rental or family member will access the outside world! You can either install one exterior door (which some may prefer) or multiple doors depending on the size/layout of the space being converted. Having options when it comes to emergency exits is very important so keep that in mind before making any changes.


Does Building An Accessory Dwelling Unit Require Permits?

Accessory Dwelling Unit requires permits no matter what type of modifications are made within your property including adding a second kitchen, electrical work, structural changes, etc., you will need to make sure that your ADU meets all local housing standards. This means having working smoke detectors, meeting the minimum insulation levels required for each unit, and more.

Permits will vary depending on the size of space being converted – but since most ADUs are smaller you’ll likely only require a set of construction drawings like blueprints signed off by both yourself/architects who designed it and then submitted to your city’s building department before making any changes. These files should include everything from measurements, wiring diagrams, etc., and be ready in case additional questions come up during inspection.


When Do I Get My Permits?

Once an architect has laid out plans they can submit them directly to the city’s building department with you or whoever is managing the project on your behalf. It’s always best to check with local authorities before starting any work just in case there are specific requirements.


Who Can Live In An Accessory Dwelling Unit?

As long as you are building within city limits, most ADUs may be rented out to tenants living off-site. While size varies depending on what kind of space is being converted, many units include one or two bedrooms, not including bathrooms and kitchenettes which would need to meet all state/local standards. However, make sure that any additional features like washer/dryer connections, etc. meet these same guidelines too. If renting, some cities will require that the tenant(s) have a parking space to live in your ADU. This is because it is considered an accessory dwelling unit and not a fully detached home/apartment which means you’ll need a driveway or garage for them to park their vehicles.

  • Provides the fundamentals to building an ADU
  • Helps navigate laws so you can be compliant
  • Shows all potential tenants what they’ll get in an ADU
  • Explains how this type of housing differs from a studio apartment 


What Are Some Common Accessory Dwelling Unit Layouts?

When looking at potential units most will include a one-bedroom, bathroom, kitchenette with enough storage for tenants but this may vary depending on what kind of space you’re converting. For example – small spaces like garages, etc., may only offer room for a bed along with essentials while large lofts can easily accommodate two bedrooms, bathrooms, and layout furniture based on needs. The best way to get started when designing an ADU is to make a list of all the must-haves and then work your way from there.

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