Yes, but only on the ADU itself. Under California law, the county assessor sets a new assessed value for the part of a property that is newly built, and the rest of the property, including your existing house, is not reassessed and keeps its base year value. The Los Angeles County Assessor lists adding an ADU or a junior ADU, attached or detached, as assessable new construction, and says the existing land and structures not involved in the new construction are not included in the reassessment.
The same rule decides whether a remodel or an addition raises your assessment, and the Assessor publishes which kinds of work count. Here is how it works, in the law’s own terms and the Assessor’s.
What the law says
Two sections of California’s Revenue and Taxation Code set this out. Section 71 says the assessor determines a new base year value for the portion of the property that was newly constructed, and that the base year value of the remainder, which did not undergo new construction, shall not be changed. Section 75.10 says that when new construction is completed, the assessor appraises it at its full value on the completion date, and that value becomes its new base year value.
So a finished ADU adds its own value to your assessment, while your house keeps its existing base year value.
What the Assessor counts as new construction
The Los Angeles County Assessor’s Office reviews the permits it receives from local building departments one by one to decide whether the work is assessable. Its published examples:
| Project | Assessable? |
|---|---|
| Adding an ADU or junior ADU, attached or detached | Yes |
| Room additions, garage additions, or additional living space | Yes |
| Adding a floor or level, including below ground | Yes |
| Converting an unfinished attic or basement into living space | Yes |
| Adding a bathroom, a garage or an elevator | Yes |
| Re-roofing | No |
| Dry rot or termite repairs | No |
| Replacing or repairing doors, windows, fences or decks | No |
Kitchen and bathroom remodels: it depends on the scope
The Assessor draws the line between maintenance and work that raises a home’s quality or extends its useful life:
| Assessable | Not assessable |
|---|---|
| Structural changes, a changed floor plan or a larger room | Replacing cabinets, countertops, flooring, fixtures or built-in appliances with items of similar quality |
| Upgrading the plumbing or electrical systems | Normal maintenance and repair, and primarily cosmetic work |
| Replacing cabinets, countertops, flooring or fixtures with upgraded materials and finishes | |
| Renovating a property or a significant portion of it down to the studs |
The Assessor notes that every project and property is different and that each permit is reviewed individually, so the table is a guide rather than a ruling on your project.
Junior ADUs
According to the Assessor, a junior ADU is created from part of a single-family home, such as a bedroom or an attached garage, and is no larger than 500 square feet. It is on the Assessor’s list of assessable new construction. When existing space is converted, the Assessor adds the increase in market value from the conversion to your current assessed value; the rest of the house is not reassessed.
Planning for it
The practical point is to budget for the added assessment on the new work when you plan an ADU, an addition or a major remodel, and to ask the Assessor’s Office about your specific project if the amount matters to the decision. The Assessor works from the permit record, which is one more reason the work should be permitted; see what an ADU is under California law for the permit side. This is general information, not tax advice.
How we handle it
We design, permit and build ADUs, including in the City of Los Angeles through ADU construction in Los Angeles, as well as room additions, kitchen remodels and bathroom remodels, with the permits each one needs.
