ADU Plans and Designs: Accessory Dwelling Units 101

black and white exterior

ADU Plans and Designs

Accessory Dwelling Unit 101

5min read
by Olesia Chikunova, ADU Specialist.

Whether you’re planning on designing an ADU to accommodate the needs of older family members or contemplating a boost in your property’s value to attract rental clients, the addition of extra livable space will surely lend an incredible helping hand both in terms of property value and making it a more comfortable and spacious area. 


Housing shortage across the United States reminded us of the good old granny flats. There is a reason the California Department of Housing has been pushing for better ADU ordinances and simplified permitting processes across the state. Other states, especially in high-density areas, follow California State laws to promote secondary houses as affordable housing options.


But before diving into the project, there are a few essential considerations, particularly regarding the ADU plans and designs that will work best for your needs — read on to learn more! 

Examples of ADU plans in 3D

Accessory Dwelling Unit: Definition & Examples

An ADU (accessory dwelling unit) is a fully functional living space in the same lot as another single-family house. An ADU ranges between 200 to 1200 square feet and includes at least one full bathroom and kitchen. 

While ADUs can take multiple forms, there are three common types (that can be classified and altered into further plans and designs to allow for more flexibility). 

  1. Interior – included in the primary house as an attic or basement transformation. It may be called a junior accessory dwelling unit if smaller than 500 sq ft and converted out of existing space.
  2. Attached – built as an additional unit to the primary residence and connected via a wall or a breezeway. No, a connecting door is not allowed. A separate entrance is required.
  3. Detached – a separate structure, like a cottage, garage, or shed. You can convert an existing accessory structure into a new tiny house that could be used as a guest house or as an independent living unit for your in-laws. You can also convert an existing accessory structure larger than 1200 sq. ft. into an ADU.

See below the video of a planned transformation from an old structurally unsafe garage to a new unit with added space for entry and a loft.

The Basics of An ADU Floor Plan

A floor plan is created by design professionals. It is a representation of your ADU design outlining all features, from essential elements like the location and layout of each room, the windows, and the doors to detailed aspects like the features of every room, such as built-in appliances, a laundry, a mudroom, a home office, etc. 


A well-designed ADU plan will provide the builder with a distinct visualization of the end results and guarantee you an accurate estimate. Construction costs have been volatile ever since the supply chains were disrupted by the COVID. 


Once the ADU plan has been finalized, a detailed construction document can be prepared and presented to the municipality to obtain a permit. Make sure to get expert support before submitting your building permit application. We see time and again inexperienced designers applying with incomplete plans. It is easy to check submittal requirements. Everything is online these days. 


The city departments must review ADU permit applications and ADU plans within 60 business days. But you lose time when you submit an incomplete application. And you delay the construction of ADU, leaving yourself open to the risks of building materials’ price increases. Until you pay plan check fees, your application is not considered as submitted.

Types of Accessory Dwelling Unit Floor Plans

An ADU floor plan can be 2D or 3D. A 2D floor plan appears more like a maze, showcasing a basic outline for the amenities in the home without a clear sense of dimension (like height or depth). If your designer offers only 2D plans, ask them to walk you through the plan, explaining what it means. Ensure the designer follows the energy consultant’s recommendations for walls and windows. 


A 3D ADU plan offers a more realistic image of the project, facilitating better placement of things along the vertical axis, like doors and windows. With an advanced 3D visualizer, you can even toggle around the plan to view it from different angles and picture it in your mind more clearly. 


We offer all our 300+ ADU plans in 3D. If you really want to avoid change orders down the line, please walk through the plan online and discuss with your designer what needs changing. Custom design from scratch is rarely necessary. Customizing a plan by moving a window or a door often makes sense, as every backyard is different. We need to consider the location of the ADU in relation to the main house and property lines.

Which ADU Plan Suits Your Needs Best?

With countless ADU plans, deciding on a single option that fulfills your needs perfectly without exceeding the available budget might get overwhelming. This is why we only show you some of the 300+ ADU plans we carry in our ADU floor plan library. We are here to simplify your ADU construction process. We want to make it easy to get started on your ADU.


A good rule of thumb is to closely view 3-5 different ADU plans, match them to your requirements and budget, and take a second opinion, preferably from a professional. It helps to list your requirements on paper. We are all human and forget things that are not top of mind. Having a checklist really helps. You may be looking at pre-approved ADU plans in hopes that you can start the project one month earlier. Still, it quickly loses its attraction if the windows of the ADU bedroom look directly toward the main house’s living room.


Don’t consider the task a buzzkill but a chance to get creative and utilize the available space as much as possible. A design professional will be able to quickly map your design on your site plan to confirm your ADU can be permitted by the local building department.


Architectural designs of backyard cottages have to complement the styles of the main home.

ADU Plan Under 750 Square Feet (with 2 bedrooms)

Staying under 750 sqft keeps the ADU project economical, as California ADU Law provides an exemption for impact fees on projects within 750 sqft. With the right design plan, a 750 sqft ADU can include 2 bedrooms, a kitchen, and a bathroom, paired with extras like a living room and laundry room. The bedrooms can then be used as a personal space, an office, or a guest bedroom. 

layout of 750 sf unit

Narrow ADU Plan For Rental

When designing an ADU plan for renting, privacy should be on the priority list of the design. (Short-term rentals are not allowed in most jurisdictions.) Property owners must focus on providing maximum privacy and space to ensure a comfortable living space for tenants. An example of such a floor plan is an ADU that offers dual suites, with bedrooms and full bathrooms on opposite ends and the lounge and kitchen joining the two. This prevents the tenants from being squeezed into close quarters while designing a seamless layout. 

ADU Plan For Entertainment

An open-plan ADU will work best for empty-nesters looking to downsize but still want a space fit for entertainment and get-togethers. A large dining and living room space with minimal partitioning walls creates better flow and makes the home appear visually bigger.

When designing an ADU plan for entertainment, an example you can take inspiration from is a 1200 square feet 2 bedroom and 2 bathroom home.

ADU Plan For College Rentals

Property owners in a high-density neighborhood can significantly benefit by using every inch of their square footage. Whether you’re living in an up-and-coming area or situated close to a university where you can rent out your space to students, an ADU is the perfect idea to boost your home’s value while making a monthly profit. 


A good idea would be to invest in a two-story ADU plan set with a 3 bedroom and 2 bathroom layout that allows you to allot one room to each renter and earn a higher profit for utilizing only 600 square feet of your backyard. 

Can I Purchase A Pre-Designed ADU Plan?

Purchasing a pre-designed ADU plan saves you considerable time and money, as all the design work has already been done. So you won’t have to hire professional design services and go into technical details like appliances, utilities, and permitting headaches. 


Suppose you’re considering investing in a pre-designed ADU plan. In that case, there are a few things to consider beforehand — apart from the budget. 

  • Decide if you want to be involved in the design process. If you want to rely on experts to give you a better and different perspective on your idea, a pre-designed ADU plan can help. 
  • Ask friends and family for suggestions. People who have recently taken up an ADU project can guide you on the better choice. 
  • Research companies that offer pre-designed ADU plans. Pre-designed plans are an easy way to get a jump start on the process.



While multiple companies offer such services, the pre-designed ADU plans on our website are practical design ideas that can be customized and altered to your lifestyle needs. Even better – the exterior walls of our ADUs can be pre-fabricated off-site. Imagine getting a custom ADU with all the benefits of a pre-fab ADU. This approach ensures the space is utilized smartly, the budget is under control, and the results make the most out of your backyard. 

Final Words 

ADU units are the perfect way to create additional living space without investing in an entirely new property, all while helping you boost the value of your home and earn a few extra bucks with rental income. 

The best decisions regarding the ADU plan and layouts can come from getting inspired by examples of ADU plan sets to create something unique and personalized or opt for a pre-designed ADU plan to allow the experts to help you. The choice totally comes down to your budget and interests! 

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