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The Cost of Building an ADU

The three main categories of cost for any ADU project are design, permit fees, and labor.


Housable can work with you to develop a custom design for your property, you can select a standard design from our library over over 200 models, or you can provide us with a design concept for drafting. Whichever direction you choose for your ADU design, starting with Housable is always free. We do not charge for preliminary reports or for an initial consultation. Get started by following the five free steps below.

Design with Housable

Step 1) Start by entering your address into our search tool on the Housable homepage and verify your email. Once you've verified your free account with Housable you can access your property report. This report contains the publicly available information about your property including ADU eligibility, other zoning information, and important details necessary for moving your project forward. In order to work with Housable you must have an account and login to our system, this is how we share files and feedback regarding your design process.

Step 2) Once you've started a free account and claimed your property report, you will need to specify your ADU preferences using our free online tool available on your account page. This tool helps us to understand what style of ADU you're looking for. If you don't know yet you can always change this later, but provide as much detail as possible.

Step 3) Book a consultation using the link in your property report. When you schedule your Zoom meeting keep in mind that we need your ADU preferences before we'll be able to provide you any specific information about pricing. Make sure you have the Zoom app downloaded and ready to go. No video camera? No problem! Zoom doesn't need you to turn your camera on to connect, you can join the consultation call with just your voice and the link should allow you to call in from your phone as well so long as you have a smart phone with the zoom app.

Step 4) Attend your free 15 minute consultation with a member of our team, they will go over all the details of your project to prepare a quote for you. Based on the information you provide, the quote should arrive within a few days.

Step 5) If you decide to move forward with your ADU design project with Housable you can either pay as you go in installments or you can use our design-bid-build process which will require you to connect us with your builder or to use a builder from our Marketplace.

The cost of your permit-set will depend on your design and the method you choose to pay; up front, installments, or design-bid-build. You will need to go through all the steps above to get specific price quote for your project.

ADU Design by Housable in Hayward California
ADU Design by Housable in Hayward, California


It is typical for architecture firms to charge upwards of $10,000-$15,000 for design and construction plans to permit an ADU project in California, excluding engineering fees and city permit fees. At Housable we have developed a process that allows you to get the customization and cost effectiveness that you need, without the high upfront design and engineering costs typically required to permit ADU projects.

Regardless of who builds your ADU or how it is built, city permit fees typically range from $2,500 to $10,000 in total, though these fees have been significantly reduced state wide in the past year. Here is a breakdown of what city fees typically cost depending on project size and scope. While many impact fees are waived for smaller ADUs, school fees are almost universal and range from $3-4 per square foot of the finished ADU which varies by municipality as well. Water and sewer connection fees vary but can cost as much as $2000 in some cities.

  • Planning Review Fees - $500-$1,000
  • Building Permit Fees - $1,500-$3,000
  • Plan inspection fees - $1,000-$3,000
  • Impact Fees - $1,500-3,500 (not applicable to ADUs under 750 sq. ft.)
  • School Fees - $1,000-2,500 (not applicable to ADUs under 500 sq. ft. of JADUs in most cases)
  • Certificate of occupancy (final building inspection sign off) - $250-$500
Other potential fees (vary widely by project and not applicable in every municipality or project):
  • Sewer hook up fee
  • New water connection 
  • Utility connection fee 
  • Driveway permit 
  • Easements
  • Land survey

Permit fees vary by municipality. If you're planning to build an ADU larger than 750 square feet, you can expect to pay some permit fees proportionate to the size of the primary home.

Zoning Permit Fee
The zoning permit is the first fee a homeowner will pay to the city. This ranges in California from a simple zoning verification letter ($25-$450) to a more complex zoning approval ($450-$4000). Sometimes zoning approval is not required or is included in the building permit. Your planning office will help you through the zoning permitting process.

Building Permit Fees
At minimum, in California, you need a building permit which includes permits for mechanical, electrical, and plumbing work in addition to individual costs attributed to each design element. Building permit costs vary and are either a fixed cost permit, sometimes inclusive of zoning approvals, or based on square footage. Building permits cost $450-$2500 (low end average) to $4500-$15,000 (high end average).

Impact Fees
If your ADU is less than 500 square feet impact fees will likely be significantly reduced or waived. If you're looking for something in the 500 to 750 square feet, expect to pay a school impact fee, connection fees for sewer and water, solar fees, and occasionally traffic impact fees. For ADUs larger than 750 square feet many of the aforementioned fees may apply. If you're in a coastal zone, you may be subject to some much larger fees, but nothing that prohibits an ADU.

Certificate of Occupancy

The last step before move-in is to obtain a certificate of occupancy. A city will either charge a fixed occupancy permit process fee or charge for the building inspector's time spent inspecting the house (2-4 hours, upwards of 8 or more). These permits typically cost $250-$500 on average.


Recent market rates for simple conversions projects or JADUs range from as low as $50,000 upwards of $150,000. Conversion projects, especially those in the primary home, are often the most affordable option because of access to electrical and plumbing, as well as loadbearing walls and the foundation.

Market rates for larger conversion projects, two story projects, new construction, or more complex designs can range anywhere from $100,000 upwards to $450,000. Most ADU projects will come in well under $300,000.

Keep in mind that the cost of materials fluctuates normally but that supply chain disruptions can cause spikes that double or even triple the cost of materials. Depending on your contract this may change the cost of your ADU. Some larger contractors purchase materials early for multiple projects ensuring they can meet their price quote, smaller contractors may need to adjust the contract to reflect changes in materials costs.

A typical project cost breakdown might look something like this:

    • ~75-85% toward construction materials and labor
    • ~10-20% toward permit fees
    • ~5-10% toward design costs

Permit fees vary significantly by municipality and the valuation of your project.