What is the ideal lot for an ADU?

There are many factors in an ADU build that have the potential to significantly alter the timeline and cost of your build. One of these is the makeup of your lot, which differs property to property. No matter if you are a current property owner or are currently seeking out an ADU-friendly property, there are some qualities of a lot that can make your build easier. Below you can find all of the answers to your lot-related questions, to help inform your lot selection or help you understand what to expect when kicking off your ADU build.

Can I build an ADU on my property? What features should my lot have?

Whether you already own a property or are looking to buy an ADU friendly property, this is one of the primary questions you will likely ask yourself before building. The ideal ADU lot has the following characteristics:

  1. Lot: Deep & flat (more space for ADU, lower site work costs)
  2. Location: 1/2 mile walking distance from bus stop (no parking required)
  3. Utilities: Public Sewer (new septic system is typically required for a new ADU)

Of course, you will be able to build an ADU on a property without the aforementioned qualities. However, your timeline and project cost will likely increase to make up for the less-than-ideal considerations of the lot.

Your jurisdiction will also have requirements based on the type of ADU you can build on your property regardless of its condition. This varies by area, although California as a whole requires cities to allow ADUs of at least 1,200 square feet, and does not allow more than one ADU on a single family property. Multifamily properties area allowed up to two ADUs. Your build will also have height requirements, which generally limit an ADU to be no larger than sixteen feet. Encinitas, Oceanside, Vista, and Carlsbad are all especially ADU-friendly cities that allow residents the most flexibility when designing their units. Although regulations will vary depending on your area and the local legislation, your contractor will be able to advise you in the correct area.

What’s the smallest lot you can build a house on?

There are no minimum lot sizes in the state of California, although you will be required to comply with setback laws for your area. “Setbacks” refer to the distance your ADU must be away from your property line, which is four feet in the state of California. It is wise to set your unit a bit farther away from the property than required, as a survey may be triggered which can extend your build’s timeline and increase the cost to build. Otherwise, your ADU size is only limited by the amount of space that can fit comfortably on your lot. The smallest an ADU can comfortably be build is roughly 450sqft, but the build depends entirely on your intended use for the space.

How close to the property line can I build an ADU?

The closest your ADU can be to your property line is four feet. This will likely trigger a survey if your property lines have not recently been assessed. Such a survey can drag out your overall build, as it may involve redrawing your property lines. Thus, it is advisable to allow your ADU as much space as possible from your property lines. However, if you are pressed for space, six feet is an ideal setback.

What should I look for when building an ADU?

When building an ADU, you should look for the flattest, most spacious portion of your property to serve as the initial pad. You will also want to be sure you stay away from encroachments like retaining walls or swimming pools, as they will compromise the integrity of your ADU’s foundation. You must also be aware of additional considerations like electrical lines that will affect how tall you are able to build. You will also need to take your city’s regulations into consideration. If you are looking for a property to buy and eventually build an ADU on, you may want to choose a jurisdiction with ADU-friendly regulations that will make the process simpler and more efficient. Many cities across the state of California have passed legislation to make builds simpler, to increase housing options, provide low-income options, and even encourage multigenerational living.

The ideal ADU lot will also have a nearby sewer system that you ADU can attach to. This will save you money on a septic system, which is the only other option to take care of the waste on your property. A that vehicles can enter and exit the property through will also save you money on your build, as you will be charged extra if no machinery can access the pad. Trenches will have to be dug by hand, alongside a number of other steps of the build. This will increase your labor cost, so it is in your best interest financially to ensure there is ample access to your property.

Can you build an ADU before the main house California?

While you can build an ADU-like structure before your main house, that unit will at first be considered a primary home and not an ADU at that point.

Some folks might want to start out with a smaller home, build some equity, then later build another larger home on the same lot and rent out the smaller home.

An ADU, by definition, cannot exist alone, as it is an accessory unit to a primary dwelling unit on a residential property. So any initial home built will be considered the primary residence and also assessed all of the fees that a new residence would incur (easily $100K+ for costlier design requirements, permits, site work requirements & right of way work). Then once you build the second larger home, you would “convert” the status of the original building to an ADU. The fees you already paid for a primary residence would typically be applied towards the new home, so you would not pay those costly primary residence permits twice.

In order to successfully reclassify a structure as an ADU, you would need to ensure the first structure you build will conform to both the requirements for a primary dwelling AND the requirements for an ADU. For instance, there are typically minimum sizes for a single-family dwelling unit based on the number of bedrooms, minimum widths etc. These requirements will vary by municipality and it’s a good start to reach out to your building department directly.

So you are still able to build an “ADU” on an empty lot if it conforms to all the standards for a primary residence – and it will initially be classified as the primary residence. Then once a new larger primary residence is later planned and permitted, the initial dwelling can be reclassified as an ADU.