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  • Writer's pictureDuff Bangs

ADU, DADU's & Mother In-law Units

They have many names depending on where you a from. In general the idea is to add a separate smaller living unit on or in an existing property with a previously established larger home.

In this blog post, we'll talk about what an Accessory Dwelling Unit is and why they might be a good idea for your property.

What do these terms mean?

Accessory Dwelling Unit (ADU)

This is a living unit that is connected to the primary structure. We will use ADU throughout this post to encompass all the below terms.

Detached Accessory Dwelling Unit (DADU)

This is a living unit that is physically detached from the primary living unit but still present on the primary parcel.

Mother In-Law unit (MIL)

This term can be used interchangably for both ADU and DADU. Typically the idea is to give a separate living unit for a family member who can be within close proximity.


It varies from one jurisdiction to the next and will be based on applicable building codes but at a minimum an ADU will contain a sleeping space, bathroom and a cooking space. The cooking space will typically contain a sink and a cooking appliance such as a range and/or microwave. In some jurisdictions, they may even require a 220 volt plug to be installed to have the ability to install a range or cooktop.

Check with your local jurisdiction for code requirements.


At a minimum, an ADU will require power, water and sewer. Again, depending on the jursdiction, it may be possible to connect to the existing home on the property or new utility connections may need to be established.

Check with your local jurisdiction, utility companies and health department for what is needed for your new ADU.


SInce the ADU is a separate living unit, it will most likely have a separate street address. Typically it will share the primatu street number such as 123 but it may have a sub address such as 123b or 123 1/2, etc.

Your local jurisdiction will help you with this.


Like any structure, most jurisdictions in the US will require a building permit for anCheckas this is a habitable structure Check with your local jurisdiction for requirements.


So why would you want to have a separate living unit on your property?

Rental income. This new ADU will allow you to be able to provide a rental unit to help pay the mortgage of the primary property.

Housing for a family member.

Sometimes it can be advantageous to have a family member living close by to take care or children or you may need to take care of an elderly parents.


Typically the size of the the ADU will be smaller than the primary residence. Again check with your local jurisdiction but sometimes the maximum size of the ADU may not exceed 800sf or 1200sf.


There are many options of where this ADU can be located.

Within the primary unit.

The ADU can be located in the basement of a primary home or it could be located in the upper floor.

Separate phyisycal location.

In the case of a Detached Accessory Dwelling Unit (DADU) these can be located in a rear yard or side yard. But typically not in a front yard.

In many cases a DADU may work very well above a garage.

That's a brief explanation of what an ADU is. Please feel free to comment or ask any questions below.

Thanks for reading!

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