Exclusions from Supplemental Assessment

Under Proposition 13 new construction, which can include actions such as demolition, is subject to reappraisal in almost all instances. The completion of construction triggers a supplemental assessment for the value added or subtracted from the prior value of the property. There are, however, times when new construction does not result in a supplemental assessment at the time of completion. 


The most common exclusion is available to owners of property who are building one or more residences for sale rather than their own use. The owner needs to file a claim form with the assessor prior to or within 30 days of commencement of construction stating that the property will not be occupied, rented or leased prior to sale to the ultimate buyer. With this claim on file, the assessor’s office enrolls construction in progress values if the construction period extends over one or more January 1 lien dates. The final supplemental for new construction is held until the property sells and is then combined with the supplemental for the purchase of the property. A person building one residence for sale, sometimes known as a speculative or “spec” house, can claim this builder’s exclusion as can a large corporation building 500 homes in a new subdivision.

Another common exclusion from supplemental assessment is the construction needed to restore a property after a calamity or other disaster. The property must be restored to the substantial equivalent of its pre-disaster condition to qualify for this exclusion. Additions or upgrades to the property beyond restoration would trigger a partial supplemental for the added value of those changes.

Other exclusions from supplemental assessment occur less frequently. Active solar systems are excluded from supplemental assessment, as are the addition of fire sprinklers and other fire suppression systems to an existing building. If a property owner is modifying an existing residence to provide accessibility for a disabled person, the accessibility construction is excluded from supplemental assessment. Finally, under certain circumstances, seismic retrofit work on an existing building can be excluded from supplemental assessment or postponed from supplemental assessment for a 15-year period.

More Information

Should you have any questions please contact Napa County Assessor John Tuteur at 707-253-4459 or by email John