In the past, if we were listing real estate in the aggregate collateral position, we've made sure that the appraisal/evaluation is less than 12 months old. This means we basically have to do an appraisal once every year, for every single mortgage we have. This requires a lot of extra employee time.
Do you mean collateral, as in collateral supporting the loan and available to liquidate if required, or do you mean aggregate asset position, as in a listing of the borrower's assets supporting the financial position?
If the first, Randy has laid out the requirements.
If the second, and the property isn't really part of the collateral supporting the loan, then it's a bank policy matter.