This depends on the nature of the property and market conditions. While many appraisers suggest an update every two to three years, you should ask for a recommendation during the initial valuation.
The most important appraisal is the first one. Once property is lost, stolen or destroyed, it is much more difficult to determine value. Insurance companies demand credible, professional appraisals before they will approve reimbursement—photos and memory are not enough. Generally, "updating" an appraisal requires a change only in the value conclusion of a report. A professional appraiser can provide an informed and helpful recommendation as to the necessity and frequency of appraisal "updates."