Planning Your Ideal ADU or JADU: Common Pitfalls to Steer Clear of in Permitting

For home owners wishing to add an individually designed tiny home to the property, Accessory Dwelling Units (ADUs) and Junior Accessory Dwelling Units (JADUs) present excellent possibilities. Whether it is a peaceful backyard retreat for retiring parents, a rental unit to supplement income, or a quiet studio apartment, these secondary residential units—built on the same property as a main dwelling—promise flexibility and affordability. However, turning your vision into reality requires navigating a complex web of design choices and legal approvals. As a professional with deep expertise in ADU and JADU development, I’ve seen homeowners stumble into permitting pitfalls that can delay projects, inflate costs, or even halt construction entirely. Here’s how to avoid common mistakes and ensure your dream unit complies with city regulations.

The Intersection of Design and Legal Approvals

Designing an ADU or a JADU is not a matter of aesthetics or design, but rather it's about finding harmony between what you envision and what is possible legally. City governments impose robust limitations on height, setbacks, size, and parking to safeguard neighborhood character and housing needs within balance. For ADUs that can be detached or attached, you might imagine a stylish 1,200-square-foot house with a deck on the rooftop. But if your zoning restricts height to 16 feet or requires a 4-foot setback from property lines, that deck could push you over the line. JADUs, 500 square feet or smaller and built within an existing single-family residence or attached garage, are even tighter. You can dream of a modern kitchenette and en-suite bathroom, but if your project does not involve expanding the original footprint, it will not qualify as a JADU under most city codes.

The secret is to begin with research. Before drawing up floor plans, check your city's zoning ordinance or ADU handbook—most cities, such as San Diego or Los Angeles, provide comprehensive online information. Even better, hire a designer or contractor who knows the local regulations. "Homeowners tend to overestimate what they can do without looking at the rules," says Jane Ellis, an experienced ADU architect. "A little due diligence early on saves months of rework down the road.

Common Pitfalls in the ADU Permit Process

The ADU permit process is a minefield for the unwary. One easy error is neglecting to observe setback requirements. The majority of cities have a minimum setback rule—typically 4 feet—from rear and side lot lines for detached ADUs. Homeowners eager to fit in as much square footage as possible might design a unit that hugs the property line, only to find their plans denied. For example, in San Diego, a two-story ADU on a residential lot must comply with these setbacks even if the underlying zone allows for less. Ignoring this can lead to costly redesigns or variances, which are not guaranteed.

Another pitfall is underestimating parking requirements. Although California state code has relaxed parking requirements—excluding ADUs near transit or under 750 square feet—some cities still mandate off-street parking in specific districts, such as coastal zones. Converting a garage into an ADU without replacing that parking space can trigger a denial if your property falls within these exceptions. “I’ve seen clients assume they’re exempt, only to discover their lot’s in a parking impact overlay,” notes Mark Torres, a permitting specialist. Always verify your property’s status with the city’s planning department.

Finally, don't forget the California Building Standards Code. ADUs must comply with fire separation distances, energy standards, and structural requirements. A homeowner may design a detached unit too close to the main dwelling, violating fire safety codes, or ignore solar panel installation mandates for new detached ADUs. These errors will delay approval or result in expensive retrofits.

JADU Permit Requirements: Modifications Restrictions

The JADU permit process is more restrictive in certain respects by virtue of its specific definition. Unlike ADUs, JADUs have to be cut from available space within the area of a single-family dwelling or attached building, without additional area allowance beyond 150 square feet for ingress/egress in some instances. This restriction catches homeowners off guard who wish to incorporate additional square footage. I had a client that moved to construct a JADU in their garage but wished to enclose the walls for an expanded bedroom," Torres recalls. "We needed to change the classification to an ADU, which changed the entire permitting landscape." 

JADUs also require owner-occupancy in most jurisdictions—either you live in the JADU or the main residence. This law, under state code (Government Code Section 65852.22), catches some investors off guard who anticipate renting out both units. Furthermore, while JADUs share a bathroom with the primary home, adding another one is likely to push the project into ADU territory. Less is needed of the kitchen—on a configuration featuring an efficiency of sink, tiny appliances, and counter space is sufficient—but codes in your area might discourage 220-volt appliances, limiting your design options.

Avoiding the Pitfalls: Tips

In order to stay clear of these pitfalls, first figure out what you want to do. Rental income is number one, or you're hosting relatives? That determines whether an ADU or a JADU is appropriate. Next, stake out your lot. Check setbacks, mark whether any structures exist, and confirm zoning online or with government representatives. In ADUs, consider pre-approved designs—many cities offer them to make the permitting process smoother—but ensure that they fit with your site restrictions.

For JADUs, remain with the existing footprint. A garage conversion is a pleasing alternative, though verify whether parking replacement isn't required in your area. Include professional help—a designer, permit expediter, or contractor can spot issues early on. "Permitting is where dreams meet reality," Ellis states. "A pro can bridge that gap."

Finally, include complete applications. Leaving out structural calculations, energy reports, or site plans can stall the ADU permit process by weeks. For JADUs, include a deed restriction if required—it's a simple mistake that leads to delays. The majority of cities have 60 days to answer, so an entire package keeps things on course.

Your Dream, Realized

Building your dream ADU or JADU is an act of balancing creativity and compliance. By understanding where design choices overlap with approval from the law, you can avoid the literal and metaphorical setbacks that undermined so many projects. Steer clear of pitfalls—failing to observe setback regulations, underestimating parking needs, or overcustomizing a JADU—and you'll be halfway to a tailored small home that increases the value of your property and your life. With careful planning and a nod to the rules, your vision can take root, one permit at a time.