California Code, Revenue and Taxation Code - RTC § 5812

(a) The base year value of a manufactured home which is purchased or which changed ownership shall be entered on the roll for the lien date next succeeding the date of the purchase or change in ownership. The value of any new construction shall be entered on the roll for the lien date next succeeding the date of completion of the new construction. The value of new construction in progress on the lien date shall be entered on the roll as of the lien date.

(b) Except as provided in subdivisions (c) and (d) of Section 5802, a manufactured home that has changed ownership or had new construction completed is subject to supplemental assessment as provided in Section 75.5.