Two story ADUs are allowed in most of San Diego County, and for many properties, they are the best way to maximize square footage on a tight lot. In fact, over 75% of cities in San Diego County allow two story ADUs under their local municipal codes. Even in cities that do not typically allow 2 story ADUs, California state law still permit a 2 story ADU up to 18 feet tall if the property is located within a 1/2 mile of a major public transit stop.
However, what you can actually build depends on several factors, including local zoning height limits, setback requirements, transit proximity, fire codes, and even how your city measures building height.
This guide explains when and where two story ADUs are allowed, how tall they can be, what types of two story ADUs you can build, and more so you can determine whether building up instead of out makes sense for your property.
Can an ADU be two stories?
In short, yes, an accessory dwelling unit can be two stories in many municipalities in greater San Diego. Many cities – including San Diego, Oceanside, Encinitas, Escondido – allow ADUs to be two stories within their own municipal code. Some cities allow you to take advantage of reduced side and rear setbacks, while others will require a 2 story ADU stay consistent with the underlying zoning. Also note that some cities have specified height limits for ADUs over garages.
Additionally, California state law – specifically SB 897 – effectively allows for a two story ADU in some cases. This is because a local agency can set size limits for ADUs, but must adhere to the following state-defined rules. The maximum size limit for an ADU cannot be less than 850 square feet for a single-bedroom unit, and 1,000 square feet for an ADU with more than one bedroom, with 4′ side and rear setbacks. Specifically regarding height limitations:
- Detached ADUs on lots with single or multifamily units must be allowed up to 16 feet in height.
- Detached ADUs within half a mile of major transit stops or high-quality transit corridors can be 18 feet tall. An additional 2 feet can be added if the ADU’s roof pitch matches the primary dwelling.
- Detached ADUs on lots with multifamily, multi-story dwellings can be 18 feet tall.
- Attached ADUs can be up to 25 feet tall or the height limitation of the primary dwelling, whichever is lower.
Note that California State ADU regulations set the floor for what local jurisdictions must allow. It’s also important to look up your local codes, as height regulations vary by city.
Can you build a two story ADU under 20′?
Yes, you can build a two story ADU under 20 feet. However, the height and overall design will be influenced by factors such as local building codes, the design’s functional considerations, and the intended use of each floor. Often, 2 story ADUs under 20 feet would have compact floor-to-ceiling heights (8′) and minimal clearance for roof structures (think flat roofs). For reference, our 2nd floor plate is 19′ from finished slab, with the slab set 8″ above grade and 9′ ceilings.
It’s also important to watch for the specific interpretation of how height is measured. Some cities count from the grade to the peak of the roof, others from the top of the foundation to the roof plate, among other interpretations. Always consult local regulations and work with a design professional to ensure compliance and practicality.
Example Two Story ADU exterior that conforms to a 20′ height limit
What types of two story guest houses are there?
When it comes to expanding your living space vertically, two story accessory dwelling units offer a range of configurations to suit diverse needs and property layouts. Here’s a closer look at the three primary types of 2 story ADUs and how they can transform your property:
ADU Over Garage (Carriage House)
Evoking the charm of historic carriage houses, modern ADUs built above garages blend functionality with style. These structures typically feature a garage on the ground level with a fully independent living space above. The design can include either an external staircase for a distinct entrance or an internal one to connect both levels seamlessly. This type of ADU is ideal for homeowners looking to maximize their property’s footprint without sacrificing parking space. A two-car garage base can comfortably support a cozy one-bedroom apartment overhead, making it a perfect rental opportunity or private retreat. Read more about what to consider for an ADU over garage.
Traditional Two Story ADU
Mirroring the classic design of a two-story home, this ADU style offers a continuous living experience with both floors dedicated to a single residence. Connected internally by a staircase, the layout allows for a separation of living spaces, typically with common areas on the ground floor and private quarters above. A 2 story ADU configuration is well suited for families or individuals seeking a spacious environment that feels like a standalone home while still being part of a larger property.
Stacked ADUs
Stacked ADUs take a modular approach by creating two distinct residences, one on each floor, without an internal connection. Access to the upper unit is typically provided by an external staircase, ensuring privacy for both levels. This setup is ideal for property owners aiming to maximize rental income or accommodate multiple households while maintaining separate living spaces. However, stacked ADUs are only allowed on properties where multiple ADUs are allows such as multi-family properties or using the San Diego Bonus ADU program. Read more about stacked ADUs.
While the architectural possibilities are vast, state and local ADU laws and building codes will ultimately guide what you can build. Partnering with a knowledgeable contractor who can conduct a thorough feasibility study is crucial. This study will assess potential challenges and ensure that your vision aligns with legal and practical realities. It’s a proactive step to identify any potential issues, from property line setbacks to height restrictions, before they become costly obstacles during construction.
How tall can your ADU be in San Diego?
Local regulations will dictate the height of your 2 story ADU. We have put together a summary of the height limits and two story regulations across Greater San Diego in the table below.
Also note that in some situations, state law allows up to 18′ or 20′, so a two story may be possible in these scenarios:
- Property is within 1/2 mile of public transit
- Lot is multifamily with existing 2+ story dwelling
It’s also important to watch for the specific interpretation of how height is measured. Some cities count from the grade to the peak of the roof, others from the top of the foundation to the roof plate… and many other interpretations. We check this during Feasibility to make sure you are covered on height.
TABLE: ADU Height Regulations by City for San Diego County for Two Story ADUs
| Jurisdiction | ADU Over Garage | Two-Story ADU | Stacked ADU |
|---|---|---|---|
Carlsbad |
Yes, with underlying setbacks. | Yes, up to 20' tall if within 1/2 mile of transit, or if attached to main home. | No, except for state rule for 18'+2' within 1/2 mile of transit. |
Chula Vista |
No, except for state rule for 18'+2' within 1/2 mile of transit or on a lot with a multifamily multistory dwelling. | No, except for state rule for 18'+2' within 1/2 mile of transit or on a lot with a multifamily multistory dwelling. | No, except for state rule for 18'+2' within 1/2 mile of transit or on a lot with a multifamily multistory dwelling. |
County of San Diego |
Yes, limited to twenty four feet in height. | Yes, limited to twenty four feet in height. | No, except for state rule for 18'+2' within 1/2 mile of transit. |
Del Mar |
No, except for state rule for 18'+2' within 1/2 mile of transit. | Yes, if attached to main home. | No, except for state rule for 18'+2' within 1/2 mile of transit. |
El Cajon |
Yes, so long as it does not exceed the height limit for the zone. | Yes, so long as it does not exceed the height limit for the zone. | Yes, so long as it does not exceed the height limit for the zone. |
Encinitas |
Yes, if within height limit of primary residence. Height measured to top of roof. | Yes, if within height limit of primary residence. | Yes, if within height limit of zone. |
Escondido |
Yes, if conforming to the height limits of the zone. | Yes, if conforming to the height limits of the zone. | Interpretation pending for “stacked” ADU connection. |
Imperial Beach |
Yes, if conforming to the height limits of the zone. | No, except for state rule for 18'+2' within 1/2 mile of transit. | Yes, if height limits are met. |
La Mesa |
Yes, if underlying zone setbacks met. Height measured to plate height. | Yes, if underlying zone setbacks met. | Interpretation pending for “stacked” ADUs. |
National City |
Yes, if underlying setbacks met. | Yes, if underlying setbacks met. | Interpretation pending for “stacked” ADUs. |
Oceanside |
Yes, if underlying zone setbacks met. | Yes, if underlying zone setbacks met. | No, unless matches height of SFR per setbacks. |
Poway |
Yes, only if no taller than SFR and setbacks met. | Yes, only if no taller than SFR and setbacks met. | Interpretation pending for “stacked” ADUs. |
San Diego |
Yes, up to 21' flat roof / 30' sloped roof + setbacks. | Yes, up to height max for zone @ 4' setback. | Yes, if underlying zone setbacks met. |
San Marcos |
Yes, if setbacks met. | No, except state 18'+2'. | No. |
Santee |
No, except state 18'+2'. Height measured floor-to-peak. | No, except state 18'+2'. | No. |
Solana Beach |
No, except state 18'+2'. | No, except state 18'+2'. | No. |
Vista |
Yes, if setbacks met. | No, except state 18'+2'. | No. |
Can you build an ADU over a garage?
Yes, many jurisdictions will allow you to build an ADU over a garage as a two story ADU. Also known as a carriage house, using an ADU over garage design is a popular option to save space. Read more about what it takes to build an ADU over a garage.
In above garage ADUs, you have the option of either adding an ADU on top of your existing garage, or building an entirely new building with an ADU above and garage underneath. Adding an ADU above an existing garage is often more difficult to budget for, as the existing condition of your house will impact the build price. For example, the existing structure may need to be reinforced to support the ADU addition. Read more about detached ADU garage conversion vs demo to start from scratch.
How much does it cost to build a 2 story ADU?
A two story ADU will vary in price, due to the complexity of the build. Additional materials and structural components are necessary, so the vertical build price will be anywhere between $300-350/sqft depending on finishes. See pricing for building our two story ADU plans.
Two story units require reinforced foundations, staircases, and additional labor & materials to reach and complete the upper levels. This is for items like scaffolding for stucco & siding work, and carrying equipment up a flight of stairs. Additionally, two story units may require larger air handling units. If you are building two stacked units, you will also need fire blocking between the units. Read more about fire separation requirements.
Many contractors charge based on square footage when constructing an ADU, so it is important to research the ADU costs and pricing breakdown surrounding your entire design & build process. Or if you are thinking about a prefab two story ADU, be sure to check the all-in costs.
Source: Snap ADU (updated January 2026)
Is it Cheaper to Build Up or Out? One-Story vs Two-Story ADUs of the Same Size
A common question we get is whether it is cheaper to build a one-story ADU or a 2 story ADU when the total square footage is the same. For example, how does a single-story 1,200 square foot ADU compare to a two-story ADU with 600 square feet per floor? In other words, is it cheaper to build up or to build out?
In most cases, the overall build cost comes out surprisingly close for a one story vs. two story build of the same overall square footage. The exact numbers depend heavily on site conditions and the pricing agreements your general contractor has in place. That said, at the time of writing, we typically see about a $10K to $15K construction savings when going two story versus one story for the same total square footage with SnapADU.
That does not mean two-story is always cheaper overall. Other project costs can easily outweigh that difference depending on the site, jurisdiction, and design choices.
Here is how the trade-offs usually balance out, followed by a side-by-side cost breakdown by trade.
Where a 2 Story ADU Is Cheaper
- Foundation, Roof, & Gutters: Your roof and foundation will be about half the size of an equivalent one-story unit, assuming if you have a simple two story design. Even though the footings need to be deeper to support the added weight, the total area of concrete and roofing materials is much less.
- Smaller Footprint: A tighter footprint and less lot coverage can help with setbacks and yard space, which may reduce grading or retaining wall requirements. It could also mean less demo for the footprint of the ADU.
Where a 2 Story ADU Costs More
- Staircase & Railings: Stairs and handrails add material and labor cost. They also introduce additional flooring, finish carpentry, and painting that would not exist in a single-story layout.
- Access & Safety: Working on an upper floor requires scaffolding, fall protection, and additional setup. Materials also need to be moved upstairs, which adds labor time and coordination.
TABLE: Comparing a Two Story vs. One Story ADU Build Cost
Below are the key differences in the build cost by trade impacted when opting for a two story build vs a one story build of the same size.
| Trade | Two Story Build vs One Story Build | Impact on a 1,200 SF Build |
| Foundation | -45% | ($21,000) |
| Framing | +10% | $7,000 |
| Roofing | -50% | ($7,000) |
| Gutters | -40% | ($1,000) |
| Finish Carpentry | +150% | $5,000 |
| Flooring | +65% | $4,000 |
| Painting | +10% | $1,000 |
| TOTAL | -5% | ($13,000) |
Source: SnapADU analysis of 2026 build costs
So Which Is Cheaper Overall?
When you compare a one-story and two-story ADU with the same total square footage, the construction cost is often close to a wash. With our current pricing, two-story builds tend to come in modestly lower on hard construction costs, but that delta can easily disappear depending on site conditions, accessibility needs, or client preferences. The decision usually comes down to constraints and priorities rather than pure cost. Height limits, available flat area, yard preservation, accessibility, and tolerance for stairs all matter more than a narrow construction cost difference.
What does a 2 story ADU floorplan look like?
Like any other ADU, a two story floorplan can vary quite a bit. There are a number of examples on our two story ADU floorplan page, which can give you a better idea of the various designs available to you, or we can create a custom floorplan. As mentioned above, only your budget and imagination limit your ADU design. However, it is important to be aware of the various considerations regarding your location, as well as fire-related requirements that will affect placement. For instance, external staircases must be not closer than 5′ from a property line.
Getting started with a two story ADU
Embarking on a two-story ADU project can be an exciting yet complex endeavor. From design considerations to navigating local regulations, there is a lot to think about. We’d be happy to talk more about your two story ADU project in depth. Fill out a Project Assessment to get started.
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