The placement of your detached accessory dwelling unit (ADU) – also known as a guest house, casita, in-law suite, or granny flat – is as crucial as your choice of floor plan and finishes. Understanding setback requirements is vital for a smooth building process, as setbacks can significantly impact both your project feasibility and cost. Below, we break down everything you need to know about ADU setbacks and how they can impact your construction project.
What is a Setback for an Accessory Dwelling Unit?
The term “setback” refers to the specific distance your ADU must be set from your property line or an easement (an easement refers to a space on which you cannot build without a variance). You may also ask what your ADU setback is from the main house – this is typically referred to as the building separation or minimum distance between structures.
Setbacks are determined based off of local jurisdiction ordinances, building type, and your property zoning. Thoughtfully considering setbacks is essential for planning an ADU, as failing to adhere to setback requirements can impact the feasibility of your project. It’s crucial to be aware of situations where proximity to setbacks can introduce additional steps and costs, or prohibit an ADU in a location entirely.
How Close to the Property Line Can I Build an ADU?
Local and state regulations will determine how close your ADU can be to the property line and to other structures on your property.
California ADU Setback Requirements
California law encourages the construction of accessory dwelling units by reducing setback requirements for side and rear property lines. Under state legislation, most single-story detached ADUs can be placed as close as 4 feet from these boundaries. This reduced setback allowance is a key feature of California’s push to streamline ADU development, making it easier for homeowners to maximize their usable lot space while complying with local regulations.
Keep in mind that while the 4-foot standard applies broadly, additional considerations – such as building height or proximity to other structures – may still influence your project. Always verify specific requirements with your local planning department to ensure compliance.
Special Considerations for San Diego ADU Setbacks
Cities in San Diego County have set their own maximum sizes for ADUs, most at 1000 or 1200 sqft. This means that, so long as your ADU complies with those size requirements and relevant height limits, you can build at just 4’ from the side and property line.
But both the size and height of the ADU will affect the setbacks. For instance, under Oceanside ADU rules, you may build an ADU of up to 1200 sqft, but if it is larger than 1000 sqft or 16′ in height (e.g. two stories), the ADU will be subject to underlying setbacks… not the 4′ reduced side and rear setbacks.
Additionally, the City of San Diego ADU regulations allow 0’ setbacks for ADUs under 16′. This means you can build an ADU right up to your side or rear property line. For two-story structures, the setback is 4′ if the property abuts another residential property.
Lastly, it’s important to understand how height is measured. Depending on jurisdiction, height could be measured from the average grade, the lowest point of the grade, or other points.
Why Maintain Larger Setbacks Than Required?
While reduced property line setbacks of four feet (or less) are legally allowed in many areas, there are compelling reasons to consider increasing the setback to at least six feet.
Construction Access and Cost Efficiency
Building at or near a zero property line often limits access for construction crews and equipment. Without adequate space, more work must be done manually, driving up labor costs and extending project timelines. A setback of at least six feet provides the room needed for efficient construction.
Fire-Rated Construction Costs
Structures built within six feet of a property line often trigger fire-rated construction requirements. Fire-rated materials, such as specialized eaves and tempered glass, can add several thousand dollars to your project.
Boundary Survey Requirements
Building closer to a property line often triggers the planning department (or inspector) to require a boundary survey and building verification survey to confirm the precise location of the property line and ensure compliance with local setback regulations. Surveys will add costs to your project. However, completing these early can help avoid costly mistakes and ensure optimal ADU placement. Read more about surveys.
Maximized Usable Space
Lastly, it’s nice to have an area for storage behind the ADU and out of sight from the main home. When you have just a 2-3′ setback, you effectively lose that entire area. But if you allow for six feet, it’s all more usable space for storage or other needs.
Design and Ventilation Flexibility
Structures closer than six feet to a property line face restrictions on wall openings, such as windows and doors. Walls between three and five feet from the property line can have openings comprising no more than 25% of the wall area, which can limit design options and natural ventilation.
ADU Setback Requirements from the Main House
In addition to setbacks from property lines, the distance between your primary dwelling and a detached ADU is a crucial consideration during the planning phase. The building separation, sometimes defined as the minimum distance between habitable structures, ensures compliance with safety codes, facilitates maintenance access, and enhances usability. Minimum building separation varies by local jurisdiction, often 6 feet or 10 feet between the ADU and the main house.
Why Maintain Setbacks Between Structures?
- Fire Safety Compliance: California Fire Code often requires a minimum distance between structures to prevent fire from spreading rapidly. In some cases, reduced distances may trigger the need for fire-rated construction, which increases costs.
- Improved Air Circulation and Light: Leaving adequate room between the main house and the ADU prevents one structure from obstructing airflow or natural light to the other, improving the overall livability of both spaces.
- Utility Access: Setbacks ensure sufficient room for installing and accessing utility lines, such as plumbing, electricity, and drainage systems, which often run between the main house and the ADU.
- Ease of Maintenance: Sufficient space between the structures allows for easier access to clean windows, repair siding, or conduct landscaping.
Key Considerations for Your ADU Setback from the Main House
By carefully planning the setback distance from the main house, you can enhance your ADU’s functionality, meet code requirements, and ensure a smooth integration of the new unit with your existing property.
- Building Orientation: Ensure the layout maximizes privacy and functionality for both the main house and the ADU.
- Access Pathways: Maintain clear pathways for movement between structures and for emergency responders.
- Local Codes: Consult your local planning department to verify specific requirements for setbacks between the ADU and the main residence.
Read more in our top 5 tips for designing the perfect ADU.
Can You Build an ADU in the Front Yard?
Yes, it is generally possible to build an ADU in your front yard, but it must comply with the underlying setbacks for your lot. However, California state law provides some protections to ensure that ADUs can still be built, even in challenging situations.
What California Law Says About Front Yard Setbacks for ADUs
California state law requires that front yard setbacks cannot prevent the construction of an ADU of at least 800 square feet. This means that local jurisdictions must ensure that their setback requirements do not unduly constrain the ability to build an ADU. According to Government Code § 65852.2, subdivisions (c) and (e), the regulations should not be so restrictive that they make it impossible to construct any type of ADU on a property.
When Can You Build an ADU in the Front Yard Setback?
Building an ADU in the front yard setback is typically only allowed if it is not feasible to place the unit elsewhere on the property. For example, this situation can occur when a property has limited space in the rear or side yards, or when the only usable outdoor space is the front yard. We have encountered scenarios where the property is bordered by a single yard that functions as both a side and front yard, making the front yard the only viable location for an ADU.
In these cases, property owners may be able to argue that there is no other space on the property that could accommodate the ADU. However, if the goal is simply to preserve a larger backyard, building an ADU in the front yard becomes more challenging. Local agencies are unlikely to waive front yard setbacks unless the ADU genuinely cannot fit elsewhere on the property.
What if You Want to Preserve Your Backyard?
If you wish to keep your backyard space open and prefer to place the ADU in the front yard, the unit will need to comply with the standard front yard setback requirements. Unlike the reduced 4-foot setbacks often allowed for side and rear yards, front yard setbacks tend to be more stringent and can vary widely depending on the jurisdiction. This means that unless the ADU is located in a spot that meets these specific requirements, it cannot be placed in the front yard for purely aesthetic or space-preservation reasons.
It’s crucial to consult with your local planning department to understand how the setback regulations apply to your property. Additionally, working with an experienced ADU builder can help ensure your project meets all necessary requirements while making the most of your available space.
What is the setback for an ADU with a Garage?
For ADUs that have garages attached to them, keep in mind that only the ADU itself will enjoy reduced setbacks. Any garage attached to the ADU will be required to comply with the underlying setbacks for the zone, which may be something more like 10′ or 15′ for the rear setback, and 5′ or 7′ for the side; check your local zoning code for specifics, as this will vary within each city and within each zone. Some cities do have specific regulations for ADUs above garages that may allow a reduced setback.
Also note that other elements like decks, porches, or staircases will also not enjoy reduced setbacks in most cases. As usual, it’s key to plan thoroughly for all aspects of your ADU build.
Corner Lot Setbacks for ADUs: What You Need to Know
When addressing the intricacies of corner lot setbacks for accessory dwelling units, it’s important to understand that the California state ADU statutes and the Housing & Community Development (HCD) handbook do not explicitly mention corner lots. This omission means that state laws do not override local regulations regarding how cities determine side versus front yards for setback purposes.
For those in the City of San Diego, for instance, the relevant local regulation is found in §113.0246 Determining Property Lines:
- Front Property Line: This is defined as the line that separates a lot from the public right-of-way or private street. On corner lots, the front property line is determined by the narrowest street frontage. This means the remaining side would be considered a street side property line… subject to 4′ setbacks for ADUs. Any larger setback would likely not be enforceable.
- Front Property Line for Double-Fronted Lots: In cases where a lot extends from one street to another, the front property line is considered to lie along both street frontages. However, if the right of vehicular access has been waived to one of the streets as required by a governmental agency, the property line adjacent to the street where access is waived is then considered the rear property line (which is great in the case of ADUs, since setbacks have been reduced to 4′ for rear).
It’s crucial for property owners to consult with local planning departments to confirm how these regulations apply to their specific lot and proposed ADU project. Local jurisdictions may have additional guidelines or requirements that impact setback determinations for corner lots.
Zones with Special Setbacks: Coastal, Very High Fire Severity
In certain zones, standard setback allowances may be overridden to prioritize safety or environmental protection:
- Coastal Zones: Additional restrictions may apply to protect views, habitats, or shoreline integrity. Read more about coastal ADUs.
- Very High Fire Hazard Severity Zones: Properties in these areas often require setbacks of 10 to 35 feet or more unless alternative fire safety measures like sprinkler systems are implemented. Read more about fire requirements for ADUs.
SnapADU performs detailed feasibility studies to account for such special conditions during the planning phase.
The insights shared in this blog are grounded in our comprehensive experience with ADU design, development, and construction. While we make every effort to provide accurate and current information, the dynamic nature of ADU regulations and industry practices means that some details may change over time. At SnapADU, we are committed to offering valuable resources and practical advice to help you confidently navigate the complexities of accessory dwelling unit projects. For tailored guidance and the latest updates, we encourage you to connect with our team of experts.
0 Comments