Detached ADU in 2023: How It’s Built, Costs, Regulations

Dec 4, 2022 | ADU

As additional dwelling units rise in popularity, it is becoming more important to learn about what the different types of ADUs can provide you. Of all the types, detached ADUs are one of the most flexible units you can construct that have several benefits associated with doing so. Before you decide to build a detached ADU rather than a different type, you should know all the benefits and drawbacks of doing so.

Developing a detached ADU can provide you with multi-generational housing, rental opportunities, non-living space options, and much more. Read on to learn everything you need to know about detached ADUs, including design tips and costs associated with building one.

What Is a Detached ADU?

An ADU is a smaller residential unit built on a single or multi-family residentially zoned lot. A detached ADU is a type of ADU that is a stand-alone dwelling separate from the primary residence but on the same lot. It is one of the most popular and recognizable types.

The other most common types of ADUs include:

  • Attached
  • Garage conversion
  • Internal

Some people refer to detached ADUs (and ADUs in general) as granny flats or guesthouses. These are just nicknames for an ADU. Other nicknames include:

  • Accessory apartment
  • Backhouse
  • Backyard bungalow
  • Carriage house
  • Coach house
  • Cottage
  • Garage house
  • In-law suite
  • Laneway homes
  • Ohana (popular in the Hawaiian Islands)
  • Secondary Dwelling Unit

It is important to note that tiny homes are different from detached ADUs in a variety of ways, including the fact that they are mobile, illegal in most backyards, and cannot be connected to the grid unless in designated areas.


How Big Can a Detached ADU Be?

California State code allows for a detached ADU to be built up to 1,200 square feet. However, cities and counties can place their own restrictions on ADU size limits, meaning where you live may be smaller.

About 391 cities and counties go by the state code and those that don’t mostly limit your detached ADU by design plans. To determine the regulations in your area, you can contact your local government or planning office or look at their websites.

Regardless of any ordinance your local jurisdiction passes, California state law guarantees that you can build an 850 square-feet one-bedroom as long as you are not violating any other codes. You can also develop a 1,000 square feet two-or-more bedroom unit and you can always build an ADU of at least 800 square feet.


Avoid D&I Fees

Development and impact fees support public improvements, services, and facilities. Everyone who develops must pay them when a primary residence is first constructed. When building a detached ADU, you can avoid development and impact (D&I) fees by keeping your unit under 750 square feet. 

If you go over 750 square feet, the D&I fees you will be charged must be proportional to the primary residence. In other words, local jurisdictions can no longer charge you excessive D&I fees like they used to be able to do.


Detached ADU Regulations

The California Department of Housing and Community Development created a cohesive set of requirements property owners must meet when developing ADUs. Local jurisdictions can add additional regulations to the ones the state mandates. These ordinances include everything from how big you can build your unit to interior layout requirements.

ADU zoning laws, setback requirements, fire sprinkler requirements, and even earthquake preparation requirements are all things you need to be aware of when developing your detached unit. To determine the regulations that apply to you, you can consult your local planning board or work with an ADU professional.


Detached ADU Costs

One of the main drawbacks to developing a detached ADU is that they are usually the most expensive ADU to develop. When building an ADU yourself, you need to create a budget from the start to determine what you can and cannot afford. Knowing how much a detached ADU will cost will determine if you can build it and how big it can be.

Everyone’s ADU project will cost differently. The size of your unit, your design choices, and your materials will all impact your ADU costs. ADU’s are required to meet all construction codes of a new house.

All of these things along with design, planning, permit acquisition, paying for a contractor, and buying materials add up pretty quickly. For example, you can expect to pay anywhere from $161,700 – $201,125 for a 499-square-foot detached ADU. If you’re looking to go bigger, expect to pay anywhere from $300,000 to $400,000 for your unit.

To get a better idea of how much your detached ADU will cost, use this ADU cost calculator.


Financing A Detached ADU

There are plenty of ADU financing opportunities available to you including:

  • Home equity loans & HELOCs
  • Cash-out refinancing
  • Personal line of credit
  • Construction loan
  • Renovation loan
  • Chattel loan
  • CDFI / local partnership loan
  • Peer-to-peer lending
  • Cash savings
  • Local governments grants and loans

A good financing opportunity you should consider is the CalHFA ADU grant which gives you up to $40k towards pre-construction costs. There are also several local government programs and loans designed to make building an ADU as affordable as possible.


Detached ADU Design Tips

You should always design your detached ADU with flexibility in mind. There are many things you can do with your unit, so plan for the fact that what you use your ADU for now may not be what you use it for in the future. Here are a few tips to help you keep your design flexible.


Keep Privacy in Mind

You may plan to have a family member live in your unit for now, but what if in the future it is a stranger? This is important to note when deciding where you will put windows and doors. Do you want a bunch of windows facing your house?

Also, consider installing a small side yard that is solely for the ADU. If you can build a privacy fence around it, do so to allow your tenants the ability to have privacy in their yard.


Use A Universal Design

Your design should be able to accommodate people of all ages and capabilities. You may have someone young in there now, but what if your aging parent wants to move in and the unit is not walker accessible? That is why you should always use a design that accommodates all ages and abilities so that you do not limit your unit’s potential.


Include A Washer and Dryer

One of the biggest ADU mistakes you can make is not including laundry units within your ADU. They make compact washer/dryer combos that can fit under counters and within closets without taking up too much space. You can also buy stackable units or consider placing them in a shared area like the garage. Your tenants will deeply thank you.


The More Storage, The Better

Think about where your potential future tenants will store their belongings. You need to maximize your space the best you can by incorporating plenty of storage area opportunities so that your tenants don’t need to rent out storage units because they can’t fit all their belongings in your ADU.

A great storage tip is using ADU appliances and furniture that save space and double as storage areas.


More Bedrooms Means More Income

If you plan on ever renting out your unit, consider incorporating as many bedrooms as possible. The market rate for your ADU rental income is dependent upon how many bedrooms you have. Make sure that each bedroom is at least 70 square feet, 7 feet in height, and contains an escape window so that it can count as a bedroom when it comes to charging rent.


Benefits Of Detached ADUs

There is a multitude of benefits associated with developing a detached ADU. Here is a look at some of the main benefits of investing in a detached ADU.


Flexibility With Design

Unlike a garage conversion that already has a base structure, you are free to design your detached ADU however you would like. It can be as big or as small as you want and can be shaped in whatever way best fits your needs. Having the freedom to design from scratch is a huge benefit to building a detached ADU in comparison to other types.


Increase Property Value

As a general rule, an ADU will increase your property value by 20% – 30%. However, a detached ADU usually gets you closer to the 30% increase since they tend to be bigger, are more customizable, offer more privacy, and can be placed anywhere on your lot.


Potential Rental Income

Detached ADUs are more private and therefore make great rental units. They are not attached to your house and have their own bathroom facilities, making them more desirable for individuals to rent from you. Plus, they tend to be bigger, meaning you can rent them out for more money.


Multi-Generational Housing

Detached ADUs make great housing opportunities for aging parents and young adults who aren’t ready to be out on their own yet. They also work great for struggling family members or long-term healthcare workers who care for someone within the home. Plus, you can use them as guest houses too!


Extra Non-Living Space

Some of the best ways to use ADUs do not involve living in them. Instead, you could benefit from having a(n):

  • Yoga studio
  • Personal gym
  • Home office
  • Pool house
  • She shed
  • Man cave
  • Art studio

The possibilities are endless when it comes to how you can best utilize your new space.


Developing A Detached ADU

Knowing where to start when it comes to ADU construction is important. Just like building any ADU, you will need to determine your costs and how you will finance them. Next, you will need to conduct a feasibility study to determine what you can and cannot build on your property. When it comes to the design stage, you have some options though.

With a detached ADU, you do not have to worry about working within existing structural designs or attaching to your main home. This frees up your design limitations, allowing you to do whatever you would like. A few options when it comes to designing your unit include:

Free floor plans are great, but typically only work in the city they are created by and are severely limited in design. Buying customizable floor plans can save you a lot of money and open up more options for design but still limit you quite a bit. Designing from scratch gives you endless possibilities for design but is more expensive, and using a pre-fab unit severely limits your design options and is often more costly than clients think it will be (due to needing a crane to install).


Permitting And Construction

Once you have your designs and plans, you will need to obtain your ADU permits before the contractor can begin construction. We recommend looking for the best ADU contractor in your area (not just a general contractor) who is fully licensed and insured, and fairly priced. Construction can last anywhere from 9 to 14 months depending on the scope of work.


Is A Detached ADU Right for You?

Detached ADUs offer a multitude of benefits to developing them. They tend to be more costly than other types of ADUs, but also give you more freedom in design and privacy. If you want to learn more about the different types of units and determine which one will work best for you, read this free ADU development guidebook, or contact us to speak with an ADU professional.

Here at Levi Design Build, we strive to create a customizable and functional living space unique to your personal style. Our team of dedicated designers, permit expediters, and builders offer a personalized approach to making your ADU dreams a reality. Reach out today for a free consultation to get you started on your ADU journey.