Pre-approved ADU plans have been gaining attention as a cost-effective and time-saving way to build accessory dwelling units (ADUs) in San Diego. At Snap ADU, we designed the pre-approved plans for both the City of Chula Vista and the City of San Marcos, and those plans are also accepted by the City of San Diego. Through a competitive bid process, we were chosen to create efficient, high-quality plans that help homeowners streamline the permitting process while maintaining cost-effective construction.
But are pre-approved plans always the right choice? In this guide, we’ll dive into the costs and benefits of using pre-approved ADU plans and help you decide when they make sense for your project. We’ll also explore when a semi-custom or fully custom approach may be a better fit.
What are Pre-Approved ADU Plans?
Pre-approved ADU plans are architectural designs that have already been reviewed and approved by local permitting authorities. These plans are designed to streamline the approval process, making it easier for homeowners to build an ADU by skipping some of the initial design and review stages.
Since the plans have already undergone a significant portion of the permitting review process, they are designed to meet local building codes and regulations, saving homeowners the time and cost of going through multiple rounds of revisions. While they offer simplicity and efficiency, pre-approved plans may be more limited in terms of customization compared to semi-custom or fully custom ADU designs.
Which Cities in California Have Pre-Approved ADU Plans?
Pre-approved ADU plans are available across several jurisdictions in California, with the aim of simplifying the process for homeowners and promoting ADU development. Below, we provide an overview of the cities offering these plans and what to expect.
San Diego County and Surrounding Areas
In San Diego County, multiple jurisdictions offer these pre-approved options to help streamline the construction of ADUs, which has helped meet rising housing demands. San Diego County, Encinitas, Escondido, Chula Vista, San Marcos, El Cajon, and Carlsbad have produced several granny flat plans to make it easier for homeowners to begin the process of adding an ADU to their property. The City of San Diego currently accepts Chula Vista, County plans and Encinitas plans. Del Mar and La Mesa also offer some inspirational plans in their ADU guides. You can view all pre-approved floor plans on our ADU Plans page and filtering for the jurisdiction under Pre-Approved Status.
New California Regulations for Pre-Approved Plans: AB 1332
AB1332 is a legislative bill in California passed in October 2023 that mandates several key requirements for local agencies regarding Accessory Dwelling Unit plans. By 2025, the bill requires local agencies to:
- Accept ADU Plan Submissions for Pre-Approval: Local agencies must accept pre-approved ADU plans from any source, without restricting who may submit them.
- Post All Pre-Approved Plans Online: All pre-approved plans must be made publicly available on the city’s website.
- Accept Other ADU Plans: Agencies may accept ADU plans that have been developed and approved by other localities within the state.
- Approve or Deny Applications Quickly: Applications for ADU permits using pre-approved plans must be approved or denied within 30 days.
This bill aims to streamline the ADU approval process, reduce bureaucratic delays, and promote the construction of more ADUs to address housing shortages.
However, we do not know many specifics yet of how cities will handle this new state requirement. As with many changes to state law, expect inconsistency in local application in the initial months. Cities will need time to adapt and also provide clear guidelines. Read about how we advocate for homeowners in these scenarios.
Evaluating Pre-Approved ADU Plans
Preapproved plans can be an excellent option for homeowners who want a straightforward build, and who do not have complex site conditions or design requirements. But they may not be ideal for those looking to tailor their ADU to fit a specific vision or challenging property layout.
Benefits of Using Pre-Approved ADU Plans
One of the major benefits of pre-approved ADU plans is the potential for some modest cost savings. Because the plans have already been reviewed and approved, homeowners save on some of the upfront design costs. Expect to save $6-8K by using an off-the-shelf set of plans.
Time savings are another key benefit. With reduced review times, you can potentially break ground sooner compared to custom-designed ADUs. Additionally, the design phase is simplified, which can help minimize the headaches that sometimes accompany designing an ADU from scratch.
Pre-approved plans are particularly useful for straightforward projects where the layout of the property and the intended use for the ADU align well with one of the available designs.
Limitations: When Pre-Approved Plans May Not Be the Best Fit
While pre-approved plans offer considerable benefits, they are not suitable for every scenario. Projects that involve complex site conditions, like steep grades or unusual lot shapes, often require custom solutions. Homeowners who have a specific vision for their ADU – whether it’s the architectural style or interior layout – might also find that pre-approved designs lack the design flexibility they need.
Even moving a door or window will likely invalidate a pre-approved plan (e.g. it will require re-drafting and go through a regular permitting process). Many homeowners find this constraint too limiting compared to the relatively inexpensive option of modifying a plan.
Does Using Pre-Approved ADU Plans Save Money?
While pre-approved plans promise some savings, it’s not always cheaper overall. Keep in mind that 90-95% of the costs of your ADU project are in construction. Many standard ADU plans, particularly those developed before 2024, were designed by architects without a primary focus on construction cost efficiency. Older plans often lacked input from builders, meaning they were not value-engineered (e.g., designed to require less material or minimize labor intensity). As a result, any savings on the design phase may be offset by higher build costs.
For instance, many pre-approved ADU plans weren’t designed with efficiency in mind: they often lack truss roofs (which are much more efficient to build), do not combine “wet” walls (leading to higher plumbing costs), and include over-engineered foundations with unnecessary bearing walls or interior footings. Additionally, many plans use non-standard window and door sizes, or custom shower and tub inserts, which can lead to missed cost savings and supply chain delays.
However, SnapADU’s pre-approved plans for the City of Chula Vista and the City of San Marcos address these concerns. Our designs use truss roofs, avoid costly interior footings, and provide flexibility for modifications, such as adjusting door and window placements and customizing kitchen or bathroom layouts. We also include Title 24 calculations to save homeowners both time and money while still allowing for necessary site-specific adjustments.
Is Using ADU Pre-Approved ADU Plans Faster?
Starting with a build-ready plan can save time compared to starting from scratch, as there is less work needed to create floorplans, elevations, and construction details. This can save up to 6-8 weeks in design time.
Under new regulations effective in 2025, local agencies are required to review pre-approved ADU plans within 30 days for the first round of feedback. This may help create a more predictable timeline. Historically, our experience is that the overall approval times are comparable with any other ADU plan. Approval times are often comparable to custom plans because much of the review process involves property-specific specs, not the floor plan itself.
Even with custom floor plans, we recommend that clients pick a plan that is closest to what they envision and make modifications from there to expedite the design process, saving both time and money.
SnapADU’s Role in Pre-Approved Plans
SnapADU has been actively involved in designing pre-approved ADU plans for cities like Chula Vista and San Marcos. Since we are a design build firm, our designs prioritize cost efficiency and construction practicality, distinguishing them from older, less efficient pre-approved plans that often lacked builder input. By focusing on value-engineering and modification flexibility, SnapADU’s plans offer a smoother pathway from design to construction.
SnapADU Chosen To Design City Pre-Approved Plans of Chula Vista and City of San Marcos
SnapADU was selected by both the City of Chula Vista and the City of San Marcos to design their pre-approved ADU plans. The selection process for each city was a competitive bid with over two dozen applicants, including architectural firms who have designed pre-approved plans for other cities in California. This achievement highlights SnapADU’s expertise and reputation in the ADU industry, showcasing our ability to deliver high-quality, efficient, and compliant ADU plans.
Chula Vista Preapproved Plans
The City of Chua Vista Development Services Department has made the preapproved plans designed by SnapADU available on their ADU website (City of Chula Vista ADU Page). Each of six floor plans is configurable, meaning you can choose how many bedrooms, where you want to have entrances, and how large of a kitchen. You can view these floor plans on our ADU Plans page which are tagged “Chula Vista”.
San Marcos Preapproved Plans
The City of San Marcos has also made the preapproved plans designed by SnapADU available on their ADU website (City of San Marcos ADU Page). Each of four floor plans has configurable options as well. You can view these floor plans on our ADU Plans page which are tagged “San Marcos”.
Are SnapADU Plans Pre-Approved?
Yes, many SnapADU plans are pre-approved by jurisdictions. SnapADU offers ADU plans specifically designed to meet the standards and requirements of certain California cities. These plans are crafted with cost-efficiency and building efficiency in mind, ensuring that they are both practical and compliant with local regulations. We have built them throughout San Diego County.
Has SnapADU Built Any Preapproved ADU plans?
Yes, we have built several of the San Diego County ADU plans and PRADU standard plans – you can check out our ADU projects here. We are happy to deliver what our clients want built. In many cases though, we find that the San Diego County Standard Plans and Encinitas PRADU plans may not end up providing the best overall value for the client.
Often we’ll end up producing semi-custom plans for clients by starting with a plan that most closely represents what they are looking for, then tweaking the layout. Many clients feel any additional design cost is worth it to design something that will be exactly fit to their needs and will best utilize the available space for the ADU.
How Do I Use a Pre-Approved ADU Plan?
Can I Submit Pre-Approved Plans As-Is?
No; all of the pre-approved plans are only about 80% complete and will always require property-specific modification and documentation. In addition to the building plans, your project will still require Title 24 energy calculations, truss calculations, storm water plan, and a site plan (also called a plot plan).
The site plan must show the property layout with the footprints of all existing and proposed structures, electrical services, fences, walls, gates, setbacks, parcel area, easements, driveways, slopes, drainage for storm water and other features. When applicable, grading plans, septic design and other plans and calculations must be created and also submitted with the pre-approved plans in order to obtain a building permit.
Additionally, most homeowners would need to make at least some amendments to the ADU floor plan. For example, a door or window may need to be moved due to site layout or constraints. ANY change means you will still need to pay for plans to be drawn up, plus then the plan is no longer “pre-approved.” Unfortunately it’s not as simple as just “editing” the San Diego county ADU plans. A new set would need to be drawn up, meaning these changes could increase the plan cost by $2-4K.
Do I Need an Architect if I Use a Pre-Approved Plan?
While you are not required to have to have an architect design & stamp your ADU plans, you will need to have a drafter produce the site plan, title 24 calculations, and any required structural calculations. This is assuming no changes to the floor plans themselves as discussed above. We also highly recommend that you perform a Feasibility Study to understand the full scope that will be required for your building project. It’s important to understand utilities in particular, as well as sitework costs like grading & foundation. Read more about the many costs of ADU projects you don’t want to forget to budget for.
What are Different Types of ADU Plans?
When designing a detached accessory dwelling unit, there are a number of different ways you can go about design and construction. ADU plans can be broken up into several different categories, each with its own pros, cons, and costs.
Pre-approved ADU plans
Certain jurisdictions have put together predesigned ADUs that are about 80% of a complete set of plans, as described above. These attempt to streamline the ADU process for homeowners by offering a design off-the-shelf. While pre-approved plans are appealing in concept, these plans typically don’t offer a savings of time or money as compared with other options, plus leave homeowners stuck unable to make changes.
SnapADU build-ready ADU plans
SnapADU offers a set of build-ready plans that we have designed to be cost-efficient for homeowners, while also including all the most-requested features in ADUs. Our design team has created these plans specifically to ensure their building efficiency, using “value engineering” to shave off what we’ve found to be unnecessary costs in features that don’t affect the livability or stability of the unit (e.g. using truss systems, using standard size doors & windows, combining wet walls). Check out 1 bedroom, 2 bedroom, 3 bedroom, 4 bedroom, and two story plans.
Semi-custom ADU plans
You can modify any of the SnapADU standard plans to ensure you are happy with the design you have chosen. Modifying will potentially add on an extra cost to your ADU, depending on the type of changes you are looking to make. Modifications are categorized by difficulty and into different types, all of which you can find in our design policy. Modifications are evaluated on a case-by-case basis to ensure these changes are feasible options for your ADU.
Full custom ADU plans
This will be the most time-intensive and expensive option, as custom ADU plans are highly technical and involve designing an ADU from scratch. While this offers a lot of freedom in regard to your ADU design, it’s important to keep in mind that certain decisions can add a lot of build cost. Your designer should be able to guide you on these choices and implications. For example, a custom sized shower will likely require full custom tiling, as opposed to an off-the-shelf shower insert and finishes. This adds up quickly, which is worth noting before entertaining the idea of a custom ADU.
Why are custom ADU plans more expensive than standard plans?
There are several reasons that choosing a full custom ADU plan is more expensive vs choosing or modifying an off-the-shelf plan.
Design time & cost. Starting on a custom design will entail many more hours of a draftsman’s time to produce. If you go full custom with architecture firms, expect to pay $15K+ for plans.
Custom sizes & elements. Custom ADUs that utilize many sizes of windows and doors will have higher material and labor costs, as well as more uncertainty on lead times for materials, which can cause delays. Conversely, in semi-custom plans, we use sizes that we know are typically available to reduce costs and potential delays if we, for instance, have a window broken in transit. Standard size materials are simply cheaper to acquire, but don’t affect the livability (think about the difference in a 48” window vs a 52” window).
Management time. Highly custom designs and material selections take more manual intervention in our processes. We’ve tried to automate as much of the ADU design/build process as we can so that we can offer a high quality product at a compelling price. Once we start deviating from this norm, our team must get involved in more one-off tasks, such as sourcing material or verifying that unique setups will work. This simply takes time and therefore has a cost.
To keep costs down, consider using a standard or semi-custom plan. We understand that full-custom is the only option for some situations, for instance on a challenging lot where the space & grading constraints necessitate it. We are happy to advise on what is possible on your lot.
We’d love to take a look at your property and help advise if you are looking at San Diego ADU plans. Fill out a property assessment to get started.
Free ADU Plans in San Diego: What You Need to Know
If you’re searching for free ADU plans in San Diego, you’re in luck. Several local jurisdictions, including San Diego County, Encinitas, Carlsbad, Chula Vista, San Marcos and others, are offering pre-approved ADU plans to the public at no cost. These free plans are part of an effort to make it easier and more affordable for homeowners to add accessory dwelling units to their properties.
Benefits of Free ADU Plans
- Simplified Planning: Free ADU plans provide a clear starting point, simplifying the design and planning stages of your project.
- Streamlined Approval Process: These pre-approved plans have already been reviewed by local building departments, which can expedite the permitting process and reduce wait times in some cases.
- Cost Savings: You may save a few thousand dollars on floor plans if you can use pre-approved plans exactly as-is. Keep in mind you will still need to have the plans plotted on your own property-specific site plan, along with other requirements.
Customization Options
While free ADU plans offer a great starting point, they may still require customization to meet your specific needs and comply with site-specific requirements. SnapADU can help you modify these plans to better fit your property and preferences, ensuring your ADU project is both functional and compliant with all local regulations.
SnapADU Preapproved Plans
In addition to the free plans provided by local jurisdictions, SnapADU offers build-ready ADU plans designed for cost efficiency and ease of construction. Our plans are tailored to address common concerns such as construction efficiency, material availability, and regulatory compliance, ensuring a smoother build process.
Making the Right Decision for Your ADU
Pre-approved ADU plans can be a powerful tool for the right projects, offering cost savings, streamlined approvals, and a faster path to construction. However, they are not one-size-fits-all. It’s important to assess the unique conditions of your property and your personal preferences to determine if a pre-approved plan makes sense for you.
At Snap ADU, we’re here to guide you through this decision-making process—whether that means choosing an efficient pre-approved option or developing a customized ADU that perfectly matches your vision. Ready to explore your options? Contact us to find the best path forward for your ADU project.
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