Accessory Dwelling Unit Guide for Ventura County – Essential New Regulations For 2023

 Ventura County ADU and Garage Conversion Guide

An ADU, otherwise known as an accessory dwelling unit or additional dwelling unit, is defined as a second structure on a residential lot in addition to the main house. These ‘dwelling units’ have been getting a lot of attention in California & Ventura County, as both the cities and state have drastically relaxed the restrictions and rules around building ADUs. This has created a boom of interest in homeowners building such units in their backyards or converting their garages into living spaces. Learn more about the specific ADU definition here

Ventura County Accessory Dwelling Unit

Here at GreatBuildz, a free service that connects homeowners in Los Angeles, Orange County, Ventura & San Diego with reliable ADU contractors, we get inquiries every day about accessory dwelling unit projects – here are some key points you need to know.

Let’s start with a discussion of the rules and guidelines which have recently changed to make accessory dwelling units much more viable for many homeowners. As one method to help assuage the housing crisis, the state of California has eased many previous restrictions for building these structures. The below guidelines have been passed at the state level, so please keep in mind that Ventura County cities will have their own specific set of rules, which are discussed further down.  

California State Accessory Dwelling Unit Changes

  • Increase in maximum accessory dwelling unit size allowed
  • Allowed on all single-family properties, with no minimum lot size requirement
  • Allowed on multi-family properties, including duplex, triplex, fourplex, and apartments
  • Greater variety of types of accessory dwelling units allowed
  • Reduced setbacks from rear/side property lines
  • Impact fees (sewer fees, school fees, etc) are being waived in some cases
  • Allows accessory dwelling units to be rented to a tenant without owner-occupancy requirements (in most cases)
  • HOA/CC&Rs cannot restrict building accessory dwelling units
  • Parking –The guideline now allows zero parking in many cases for the accessory dwelling unit, as long as it’s near transit.
  • City approvals – Accessory dwelling units now, in many cases, don’t require any ‘discretionary’ approval, meaning that you don’t need approvals from the city planning department, neighbors, planning boards, etc, as long as you meet the established guidelines. So, getting the right to build an accessory dwelling unit is just a matter of submitting plans to the building department and going through the plancheck process to obtain a building permit. But, start by speaking with the staff at your Planning Department to confirm there are no constraints to building an ADU in your city.

Ventura County ADU Guidelines

Each city in Ventura County is enacting its own guidelines that generally follow the lead of the state rules but may have its own specific differences. Below are resources on Ventura County and various city’s accessory dwelling unit guidelines:

County of Ventura Accessory Dwelling Unit Guidelines

Thousand Oaks ADU Regulations

Simi Valley Accessory Dwelling Unit Guidelines

Moorpark Accessory Dwelling Unit Process and Submittal Checklist

Camarillo ADU and Garage Conversion Rules

Oxnard ADU Regulations

Ventura City ADU Laws

What kind of Accessory Dwelling Units Are There?

The two primary options are either building a new, free-standing unit in the backyard or converting an existing garage to an accessory dwelling unit. A garage conversion is the most cost-effective option because the basic structure already exists. The downside is the limitation in size – most 2-car garages are only 300-400 square feet. This is still enough space for a ‘studio’ unit or a small 1-bedroom, with both a kitchen and a bathroom.

A newly built accessory dwelling unit can take many forms. It can be attached to the existing family home, attached to a garage in the back of your property, or detached completely. It can be one or two stories, with a maximum height of 25 feet.

In most cases, it must be in the backyard and not in front of your main house. A new detached accessory unit can be a maximum of 1,200sf, while an addition attached to an existing home is limited to the lesser of either 1,200sf or 50% of the size of the current home. A 400-600sf accessory dwelling unit is ideal for a one-bedroom plan and a 600-1200sf structure is enough to be one or two stories, with up to three bedrooms and two or three baths.

Why build an ADU on your property?

Many homeowners are excited about the modified guidelines and are now exploring the possibility of building an ADU or ‘granny flat’ on their property, but why? It comes down to two things: their ability to add living space to their property in a simplified manner and the tremendous variety of potential uses of an accessory dwelling unit.

Adding space to an existing house in the past meant building an ‘addition’ or second story, which was challenging. Not only was it often costly, time-consuming, and usually required considerable changes to the existing layout of the home, but it also meant living through the dust and mess of construction in your home. A second-story addition is an even more significant project, which will invariably require the home occupants to move out during construction.

An accessory dwelling unit solves many of these problems and allows for a lot of flexibility. Some homeowners are building them as extra space (an office or guest house), a music or yoga studio, a mancave or she-shed, or a dwelling for their retired parents or grown children. Beyond that, it’s also possible for homeowners to use them as a rental unit for additional income. I’ve also heard from several retired homeowners planning to build an accessory dwelling unit so they can move into it (as a way to downsize) and rent their primary home as a source for retirement income. That’s an impressive idea.

Ventura County Accessory Dwelling Unit Floor Plan

How much does an accessory dwelling unit cost?

An accessory dwelling unit will vary in cost depending on the options and size you choose. As I discussed, the most cost-effective option is to convert an existing detached garage to an accessory dwelling unit.

Since the major components already exist in a garage, this build-out requires items such as constructing the fourth wall (where the garage door is currently), adding interior walls, a kitchen, bathroom, flooring, etc; adding doors and windows, plumbing, electrical, HVAC, insulation, and a new sewer line that connects to the sewer lateral on the property.

The construction cost for an ADU garage conversion usually ranges $90,000-$120,000 depending on location and the homeowner’s requirements. Costs will go up if the garage has a lot of deferred maintenance such as a cracked floor or leaky roof. Costs to construct a brand new ADU will vary considerably based on size, the number of stories, location, access, etc, but will generally range from $100,000-$400,000. A good rule of thumb is to assume $300-$400 per square foot – the bigger the space, the lower cost per square foot. If you’re considering ‘building up’ with a 2-story (or second story) accessory dwelling unit, costs will go up as well. Check out our ADU scope checklist to determine what items need to be included in your ADU project budget,

See More: 5 Best ADU Cost-Saving Tips

How do I pay for an accessory dwelling unit?

There are multiple ways to finance an accessory dwelling unit project. Obviously, homeowners can pay for it from their own savings. Or they can finance this project by taking out a home equity line of credit, getting a construction loan from their bank, or using a home renovation loan that offers a quick processing timeline, but does come with a higher interest rate, from a company like RenoFi, Lightstream or SoFi.

What is the process of building an accessory dwelling unit?

This process begins with the homeowner meeting one or more experienced ADU contractors, who will come to the home to discuss the project and provide some guidance about the constraints, size, design, estimated costs, etc. Once the owner and contractor decide on the basic parameters, either one can bring in an architect or a plan designer to start the architectural plans. Garage conversion or ADU plans should cost between $7000 – $20,000 depending on complexity.

Local building codes continue to change over the years, so make sure your architect or designer has experience with ADUs in your specific city or area. Ask them if there are any newer building requirements in your area such as solar panels, fire sprinklers or other energy efficient guidelines.

Once the plans are complete and approved by the owner, contractors can prepare a detailed estimate/bid. Next, the owner will choose their desired contractor and sign an agreement for the work. Either the architect or contractor can submit the plan set to the building department for plan check and coordinate the process until a building permit is issued. Finally, construction can start.

How long does it take to build an ADU?

The timing depends on whether you are doing a garage conversion versus a new construction project. For a garage conversion, expect the entire process to take 3-6 months, which includes the timing to design the plans, the turnaround time for the city to do the plan check, and finally, the construction process – which often takes about 2-3 months. A new ADU will take longer for the construction process, so you can expect the whole process to take 6-9 months, with the construction phase taking 3-6 months.

Finding The Right Team – How do I hire a good ADU contractor?

When looking to build an ADU or even starting to research the idea, I suggest looking for only local, licensed general contractors. No other contractors are qualified to do this sort of major construction and using an unlicensed contractor or handyman would be a big risk. Any qualified contractor should have both General Liability and Workers’ Compensation insurance as well as a bond.

Any contractors you speak with, always confirm they have experience with ADU projects. It is best to hire a contractor who’s built additions and garage conversions and knows the potential problems and solutions. There are several other criteria you should use in choosing a contractor, not including their price.

Watch More: GreatBuildz Co-Founder Paul Dashevsky discusses what to look for in a good general contractor

Ventura County Accessory Dwelling Unit

What to look for in a reliable contractor

    • Valid and current contractor’s license

It’s extremely important to check a license on the Contractors State License Board website to verify it’s active, there are no disciplinary issues, and it has Workers’ Compensation insurance associated with it (assuming the GC has employees).

    • Insurance

Always get a copy of the Contractor’s insurance certificate and make sure that it isn’t expired. It could be a good idea to call the insurance broker, just to be sure. There have been cases where uninsured contractors have ‘Photoshopped’ their insurance papers to trick homeowners, so you can never be too careful. All quality, reputable ADU contractors will carry both Liability and Workers Compensation Insurance. Hiring a contractor with sufficient insurance will alleviate you from the financial stress of any potential issues that arise during the project.

Pro-tip: Contact your own homeowner’s insurance agent before you start your project to confirm if your existing coverage is sufficient during and after the ADU’s construction. If you plan to rent the ADU to tenants, you may need a supplemental ‘landlord policy’.

    • Excellent references

Ask all contractors for at least three references you can call. It’s important to call and ask these people about their experience and satisfaction with the quality of the contractor’s work. If you can even get some pictures of the work, even better.

    • Glowing online reviews

It’s a good idea to do a Google/Yelp/Social Media search of the contractor to check for any major red flags. Read all reviews you can find about their business, and don’t be afraid to address what you found with the contractor if there is anything surprising. Bear in mind that just because they have hundreds of positive reviews, it may not necessarily mean they are the best, as there are more and more fake reviews out there. Additionally, some of the best contractors work primarily off personal referrals and thus haven’t had much of a need to develop a website or bolster their online presence.

I’ve written a detailed article specifically on the topic of hiring an ADU contractor. If you’re currently in the process, take a look at it here: 


At GreatBuildz, we take contractor screening seriously. We take all the steps above, in addition to running a background/financial check and requiring contractors to sign our 20-point Code of Conduct. Feel free to call our free service and our friendly staff will match you with several fully vetted, honest contractors in Los Angeles, Orange County, Ventura & San Diego who are experienced with ADUs. For more info, visit or call 818.317.3567 today.

Hi, we're Paul and Jon - Co-Founders of GreatBuildz. We believe everyone deserves to find a great contractor, have a stress-free renovation, and enjoy their beautiful new space. There are so many contractors out there and it's often hard to tell the good from the bad... until it's too late. We started our company to help simplify your contractor search and help you have a stress-free renovation experience. We're always available to help, no matter where you are in the process. Click here to learn more about our story.

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