New Construction
Building an Improvement: If you own a parcel of land and build a structure (a house, outbuilding or garage), this will usually increase the value of the property. California statutes refer to such structures as improvements. The Assessor is required to add the value of these improvements to the assessment roll. The land value will not usually be changed due to new construction of a structure.
Adding New Area: If you increase the living area of your home you have completed "new construction." Since new construction typically increase the value of a property, the Assessor must add the value of the addition, but only value associated with the new addition.
Maintenance
To maintain your property's current value, you might need to paint your home or make some repairs. Typically, normal maintenance (such as painting or a new roof) would not cause a reappraisal and there would be no new assessment added by the Assessor.
Rehabilitation: A complete rehabilitation of a property, which makes it substantially the equivalent of new or changes the use of the property, is considered new construction and does require reappraisal.