A couple looking at a laptop with the words Can You Even Build an ADU? across the middle

Accessory dwelling units (ADUs) – sometimes known as “backyard cottages” or “granny flats” – are independent residences built on the same plot of land as a larger, primary residence.

A typical ADU can be anywhere between 600-1,200 square feet in size. It can serve as a home for aging parents, a home office, or as a rental property that can be used to earn some extra income every month.

Before you start designing and building an ADU, you must first ensure that your lot is eligible for ADU construction, under local zoning laws and development standards. Laws vary by location, but the steps you need to take to find out will be pretty much the same no matter where you live.

To access the zoning code that’s applicable to your home, you can check whether or not the local government website has a “zoning” section. For instance, if you want to build an ADU in the city of Denver, you can easily access the zoning code through denvergov.org/zoning, which will help you determine your zone district.

Graphic showing the difference between an internal attached, external attached, and detached ADU.
The City of Denver website even has a helpful graphic to explain the different types of ADUs. Courtesy of denvergov.org.

If you’re planning to build an ADU in Los Angeles, on the other hand, you can access the zoning code by contacting the Los Angeles County Department of Regional Planning, either by telephone or via email. Click here to learn more about the housing market in California, and the need for new ADUs.

You can also search the department’s website for an online copy of the zoning ordinance. To obtain the required zoning information on this website, you can use the department’s GIS-Net mapping application.

No matter where your property is located, you can usually find out all the necessary zoning information by contacting the municipal planning department. The zoning laws for any location are usually executed by the planning department.

The Importance Of Lot Size For ADU Construction

The size of your property is one of the major factors that will determine whether or not you can build an ADU in compliance with local zoning codes and regulations. Different zone districts – even those located within the same city or state – may not always follow the same rules.

Photo of a new construction suburban neighborhood. Each neighborhood may have its own regulations about ADU construction.
What you are allowed to build will depend not just on your state, city and county, but could come down to your individual neighborhood.

The minimum lot size needed to build an ADU may vary from one neighborhood to another. In some neighborhoods, you may not be permitted to build an ADU due to the (relatively small) size of your lot, while in a different neighborhood in the same city, an ADU might be legally constructed in a lot of the same size.

Before you spend any money on the ADU construction project, therefore, you should ask your chosen contractor or architect to learn everything they can about the zoning code for your neighborhood, and explain it to you in detail.

To determine the size of your lot, you simply have to check your annual property tax statement. The lot size will most probably be mentioned in the statement.

The zoning code and lot size will determine how big your ADU can be. Naturally, if you own a bigger plot of land, you will be able to build a bigger ADU on it. However, different zoning codes might allow for differently sized ADUs, even when the size of the lot is the same.

The fixed costs of building an ADU remain the same, regardless of the size of the structure. So, you should find out the maximum size of a potential ADU, given the size of your lot and the local zoning code even if you think you’ll ultimately build a smaller one.

What Are Zoning Laws?

You need a copy of the zoning code to determine whether or not you can legally build an ADU on your lot, as well as the shape and size of the ADU that you’re allowed to build in your zone district.

The zoning code comprises all the rules and regulations that are used by local governments to identify the types of land uses that are either permitted or prohibited in a certain area. These zoning laws also facilitate the standardization of building height and lot size in a given area. In short, the zoning code ensures that all the land in a particular zoning district is used in a manner that is safe, responsible, and mutually compatible.  

Residential, commercial, and industrial zoning are the three most common types of zoning districts found in government zoning ordinances. In this article, we are focusing on residential zoning. 

Navigating the zoning code might be easier with the help of an expert, such as a builder or architect. However, if you already have some experience in this area, you might be able to figure it out on your own.

If you do decide to use the services of an expert, ask them how many ADUs they’ve constructed. Experience counts for a lot. And you do not want to spend time and money on having an ADU designed, only for the plans to not meet the requirements of the zoning code. (Learn more about the practical elements of ADU construction here.)

If you live in a standalone, single-family home, then you will have to live on-site (in the primary residence) when renting out your ADU, in most states. You may also choose to live in the ADU and rent out the primary residence, if you require less space or need to earn more rental income than an ADU can provide. (Click here to learn more about ADUs as rental properties.)

In either case, the utilities should be shared between the primary residence and the ADU, whenever possible.

Steps To Find Out If Your Property Is Zoned To Build An ADU

To check the local zoning laws that apply to your property, you just need to follow a few simple steps. For the best results, follow these steps carefully before you start designing your new ADU.

1. Find Out The Assessor’s Parcel Number (APN)

The first thing you need to do is find out the assessor’s parcel number or APN assigned to your property. APNs are assigned by the local tax authority to parcels of real estate located within a particular jurisdiction, for the purpose of record-keeping and identification.

You will need to visit the county assessor’s office, and provide them with your home’s location and address, to get your APN. Each APN is unique and can be used to determine whether your property falls within the boundaries of the city or the county.

Photo of a sign reading "assessor's office" on the side of a concrete planter box full of lavender.
Sometimes the information you need will be online, but you might have to physically visit an office or two as well.

This is because cities and counties will usually have their own individual zoning ordinances. The zoning ordinance is simply a formal categorization of all the land-use policies and regulations applicable to a particular geographical area.

So, you will need to know where exactly your property is located, in order to understand which zoning ordinance is applicable to you and what land-use regulations you should follow. Nowadays, you might also be able to find your APN online, by searching for your address on the local county assessor’s official website.

2. Check Zoning Maps

Once you have discovered the exact location of your home within the city or county boundaries, you will have to obtain and review a zoning map to identify how your property is zoned. The city zoning laws will typically override those of the county, if the house is located within city limits.

The zoning map will show you how the area is divided into a variety of land-use zones or districts. The zoning map will also help you locate the precise boundaries of residential, industrial, and commercial zoning districts in your area.

Some jurisdictions are now posting zoning maps on their website, to make them more accessible for the public. So be sure to check if you can find the relevant zoning map online, before you pay a visit to the local zoning office or city hall.

Obtaining the zoning map will help you find the zoning ordinance that is applicable to your property. You will need this ordinance to find out whether or not your home is zoned to build an ADU.

3. Read Through The Applicable Zoning Ordinance

Now that you have used the APN and the zoning map to find the applicable ordinance, it is time to dive straight into it and learn about all the allowed uses for your lot. The ordinance will tell you weather or not you can legally build an ADU on your property.

By reading it, you will also learn about any building design standards that you need to abide by when constructing your ADU. Some jurisdictions post the entire zoning code on their website, but this is not always the case. You may have to visit the city attorney’s office or the municipal clerk’s office to get a copy of the ordinance.

The types of dwellings that can be legally built may vary from one residential zoning district to another. The ordinance will help you determine whether the zoning district in which your property is located allows you to build an ADU on your lot, how big this ADU can be, and whether or not you can rent it out for extra income.

If you have any trouble interpreting the local zoning laws, you can seek help from your lawyer, a local government official, or a trusted builder.

4. Visit Your Local Planning & Building Department

You can pay a visit to the Planning and Building Department of your city or county, in order to seek advice or help from the professionals who are in charge of enforcing the zoning laws and regulations. They might provide you with valuable advice (completely free of charge) on the best way to build an ADU while following all the local zoning laws.

Photo of hands (two people) reviewing papers on a clipboard with a pen.
Don’t be afraid to ask questions if you don’t understand your local laws.

You should especially make an appointment with the Planning and Building Department if you have any outstanding questions or doubts after reading through the zoning ordinance.

Once your ADU has been designed, officials from this department will review the design to ensure that it is compatible with all local regulations, and to see if it needs any changes before the construction can begin.

Concluding Note

Building an ADU can be a great way to increase the available space at home, earn some rental income, and add value to your property. However, to get any of these benefits, you have to first ensure that the property is fully legal.

You will not be able to get the proper permits and licenses for the construction of your ADU if it doesn’t abide by the local zoning laws. An illegal ADU will also make it difficult for you to sell or refinance your home in the future.

So follow the above-mentioned steps to find out whether or not you can legally build an ADU on your property. If an ADU is allowed, make sure you design and construct it in accordance with all the local zoning regulations.

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