Will your property taxes get reassessed if you build an ADU?

Yes, building an ADU will affect your assessed value for property taxes. However, it will only affect the marginal value of the ADU. The existing home will not be reassessed.

For Example the Santa Clara County Assessor's Office will determine the assessed value of your ADU by considering the following factors:

  • The size and square footage of the ADU
  • The quality and condition of the ADU
  • The location of the ADU on your property
  • The comparable sales of other ADUs in your area

Once the assessed value of your ADU has been determined, it will be added to the assessed value of your existing home to calculate your total assessed value for property taxes.

Here is an example of how building an ADU could affect your property taxes:

Existing home:

  • Assessed value: $3,000,000
  • Property tax rate: 1%


  • Size: 500 square feet
  • Assessed value: $200,000

Total assessed value:

  • $3,200,000

Property taxes:

  • $32,000 (1% x $3,200,000)

In this example, the homeowner's property taxes would increase by $2,000 per year after building an ADU.

It is important to note that the actual impact of building an ADU on your property taxes will vary depending on the specific factors mentioned above. If you have any questions or concerns, you should contact your County Assessor's Office.


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