ADU Plans and Designs: Accessory Dwelling Units 101

Whether you’re planning an ADU to accommodate the needs of family members or contemplating a rental unit, the addition of extra livable space will surely increase your property value. 

ADUs and ADU plans come in a wide array of styles, with the primary residence as a guiding influence. We want our backyards to look cohesive. The architectural designs of backyard cottages have to complement the roof style and exterior finish of the main residence.

Housing shortage across the United States reminded us of the good old granny flats. Granny flats have been elevated: the prototype is being used not only for mother-in-law suites but also as housing for adult children who cannot afford to buy a condo or a single-family property in the same area. 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 an affordable housing option in their local regulations.

But before diving into the project, there are a few essential considerations regarding the ADU plans and designs that will work best for your needs.

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.

Design professionals create a floor plan. It is a representation of your ADU design outlining all key features. These detailed plans show essential elements like the location and layout of each room, the windows, the doors, 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 inexperienced designers applying with incomplete plans time and again. It is easy to check submittal requirements. Everything is online these days. 

The city departments must review ADU permit applications within 60 business days in California. But you lose time when you submit an incomplete application. You delay the start of construction of ADU, leaving yourself open to the risks of price increases for building materials. You must pay plan check fees before your application is considered as submitted.

An Accessory Dwelling Unit floor plan can be 2D (traditional solution) or 3D, often called a “dollhouse.” 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 its flow and zones, furniture, and fixture locations. 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 more clearly in your mind. 

We offer all our 300+ 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 to be changed. A 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.

With countless ADU plan sets on hand, 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 500+ plans that we carry in our ADU floor plan library. We are here to simplify your ADU construction process. Start with the backyard, see what fits, and then consider costs. 

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 on top of our minds. 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; consider it a chance to get creative and utilize the available space as much as possible. A design professional can quickly map your design on your site plan to confirm that your ADU can be permitted by the local building department.

If you’re thinking of investing in a custom-designed ADU plan, there are a few things to consider beforehand—apart from the budget:

1. Decide how you want to be involved in the design process. If you want to rely on experts to create a unique architectural design, an ADU designer or architect can definitely help. 
2. Ask friends and family for suggestions. People who have recently taken on an ADU project can guide you to the better choice. 
3. Working on a custom design from scratch does incur extra costs.

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. 

This two-bedroom ADU plan features an open and airy design, with two bedrooms and a compact bathroom. It is great for small families or elderly parents who love entertaining guests! There is even sheltered outdoor space to further promote a sense of openness.

The wooden flooring creates the right welcoming ambiance. The windows also ensure that there is natural light in every space.

Open living area

Residents can unwind in the bright and airy open living area, which features a seamless flow between the kitchen, dining, and living room. Imagine cozy evenings spent binge-watching your favorite shows or enjoying a lively game night, with everyone interacting no matter where they are. The open layout allows for efficient use of space.

Kitchen

The modern kitchen boasts ample counter space and sleek cabinetry. It will inspire you to whip up delicious meals while conversing with loved ones. Integrated appliances create a functional space for both cooking and casual dining. And there’s also sufficient storage space to keep essentials tucked away.

Bedrooms

The two bedrooms offer a tranquil retreat. Each features ample closet space and dark wooden flooring for added comfort. Large windows add natural light and create a relaxing ambiance.

Bathroom

The well-appointed bathroom provides everything needed for convenience. Residents can enjoy a relaxing shower with modern fixtures and stylish finishes.

You can always opt for the loft if you need more storage space. Lofts have become a premium feature for these compact homes, where every extra square foot matters. They are not an ideal option for older adults using the space; you may need to dedicate space for proper stairs, not just a ladder, but lofts offer an invaluable resource of additional storage space.

Purchasing a pre-designed ADU plan saves you some time and money, as all the design work has already been done. 

Pre-designed plans are an easy way to get a jump start on the process. However, you and your design professional need to consider specific site conditions. 

Pre-designed plans are a good start, but they often require some customization for your backyard and to local regulations (e.g., egress windows, bathroom size, choice of building materials). Site plans are also required in most cities and are not offered by online plan sellers.

The pre-designed ADU plans offered 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 you will get a custom ADU with all the benefits of a prefab ADU. This approach ensures the space is utilized smartly, the budget is under control, and the results make the most out of your backyard. You are welcome to our treasure trove of ADU plans. Explore at leisure.

With a pre-approved plan, you won’t have to hire professional design services and discuss technical details like appliances and utilities, and it may seem like you can avoid permitting headaches. 

That said, pre-approved plans are overrated.

Is there data to support the popular opinion that pre-approved plans work? 

They definitely benefit modular companies. However, most of their plans are already approved by the State, and building inspections happen at the factory level.

A 2022 survey conducted for the San Joaquin Valley Regional Early Action Planning (REAP) Report asked city and county staff about various housing topics, including accessory dwelling units. From this survey, 12.5 percent of survey respondents stated they offer pre-approved ADU plans for residents to use for projects, while 34.38 percent of respondents have pre-approved ADU plans in progress. Respondent jurisdictions generally offer between two and eight pre-approved ADU plans. These pre-approved plans have initially not been as successful in producing new housing as hoped. Approximately 73 percent of respondents say their pre-approved plans have not been used to producenew housing. Conversely, over 26 percent of respondents say their plans have been used. 

A hypothesis for what may be the reason: all backyards are different, and not only by the shape of a parcel. But also by what has been added to the backyard by the owners – fruit trees and garden beds, swimming pools, accessory structures, fireplaces, and patios. If one wants to keep the aesthetic appeal of one’s backyard, some customization will be required. Fortunately, this does not mean you need to opt for a traditional custom-built. There are prefab options that work well with custom plans. This is the right direction to find an ideal solution for your backyard. 

One more side of the coin: the designer can charge more for a pre-approved plan without anyone being the wiser.

Check with your city to see how their agreement with the designer of those plans is structured. We often see on the pre-approved plans the verbiage that the pre-approved design belongs to the architect. So, without a written agreement from that architect, you will be violating their intellectual property rights. Oops.

Site plans are required for all building permits. If your house is located in an area with complicated soil conditions, a structural engineer may be required to confirm the foundation design and run additional structural calculations.

Check out our ADU Planner for a clear road map.

P.S. This service is complementary, however login is required.  These plans are simply suggestions to help you get started with ADU projects, you are free to explore and find alternatives that suit your needs through your own research. The content contains affiliate links for which we may receive compensation.