Will a second story raise my property taxes?

The State Board of Equalization's page on new construction, at boe.ca.gov (opens in a new tab), says that when construction is completed, "the Assessor must determine the new base year value for that portion of any newly constructed taxable real property." It then says: "The base year value of the remainder of the property, which has not undergone new construction, shall not be changed."

The same page defines new construction to include "any addition to real property, whether land or improvements, including fixtures, since the last lien date." A second story is an addition to the improvements, so it is new construction under that definition.

The new floor gets its own base year value when the work is complete. The house you already had, and the land under it, keep the base year value they have now; in the Board's words, that value "shall not be changed." Building a second story does not reopen the value of what was already there.

That is the plain reading of the Board's sentences. What it does to your bill, how the county applies it to your parcel, and when the bill arrives are the assessor's answers to give.

The Board's page also says: "New construction in progress on the lien date shall be appraised at its full value", and that at completion "the entire portion of newly constructed property shall be reappraised at its full value." A second story that runs across a lien date can be valued while it is unfinished and again when it is done. Ask the assessor's office how that timing works on a project of your length.

Four questions, to the Los Angeles County Assessor (opens in a new tab): how the newly built portion will be valued and when; how the existing base year value is carried forward on the rest of the parcel; whether a supplemental bill follows completion and when it arrives; and how a project that runs across a lien date is handled. Write the answers down with the date and the name of the person who gave them.

It is not tax advice, and it quotes one source: the State Board of Equalization's own page, read on 2026-10-29. The Board's page carries no stated update date of its own. The county assessor applies the rule to your parcel; your tax professional applies it to your return. What the page gives you is the rule in the state's words, so you walk into those conversations knowing what to ask.

The build itself, from the structural look to the day the roof comes off, is on the second-story additions page.