What is the Cheapest Way to Build an ADU in California?

If you are dreaming of creating an accessory dwelling unit (ADU), but are afraid of its price, you are not alone. Good news? You can make it economical, either if you know the cheapest way to make an ADU permit in San Diego, California, and at the same time, the permit process is easy, whether you are in Los Angeles, Riverside, or San Diego, achieving ADU permits in San Diego.

1. Go for a Garage Conversion

One of the fastest and affordable ADU options is to change your garage.

  • The foundation and walls already exist.

  • This reduces the time and cost of construction.

  • Extensive excavation work can often be avoided.

If you are in Southern California, you will still need a permit, so check your local needs, including the process of the ADU permit in San Diego, if it is your area.


2. Keep It Under 750 Square Feet

Small adu are very effective. By keeping your design less than 750 square feet, you can avoid some impact fees in California. This is immediate savings.


3. Choose a Simple, Smart Design

Detailed roof, custom size and luxurious finish look good until the bill comes. Keep it simple to save money.


4. Consider Prefab or Modular ADUs

Prefabs are already made in ADU factories and are sent to your site.

  • Low labor cost.

  • Fast construction time.

  • Many ADUs come with pre-eminent plans, making it easy to obtain an ADU permit in San Diego or other cities.



5. Do It Yourself (Partially)

You can do some work yourself to reduce the cost - painting, landscaping, and interior finishing. But electrical, plumbing and structural work should be handed over to licensed professionals so that they can pass inspection..


6. Pick Affordable Yet Durable Materials

Do not use imported marble. Choose Quartz Countertops, Vinyl Plank Floor and Affordable Cabinetry, which will look good but will not have heavy pockets.


7. Work With an ADU Specialist

An adu contractor, familiar with the Rules of California, can save your time, money and trouble - especially in areas such as San Diego, where information about the ADU permit process can save expensive delays.


Final Takeaway

The most economical ADU construction in California is the use of existing structures, keeping the size minimal and simplifying the design. Whether you are converting garages to the Rivaraside or getting your ADU permit in San Diego, an affordable ADU is possible with the right strategy.


FAQ – One-Line Answers

1. What’s the cheapest way to build an ADU in California?
A garage conversion is usually the most affordable.

2. How much does a garage conversion ADU cost?
Often $80,000–$120,000, depending on location and finishes.

3. Are prefab ADUs cheaper?
Yes, they can be 10–20% less than traditional builds.

4. Do small ADUs avoid fees?
Units under 750 sq. ft. often skip impact fees.

5. Do I need a permit for a cheap ADU in San Diego?
Yes — getting your ADU permit in San Diego is required before construction.