The bank is making a loan on 150 acres and there is a cabin on the property which is located in a flood zone. The bank completed an in-house evaluation which does not include the replacement cost only market value. So we are not sure how to determine how much flood insurance is needed.

I would always want a certified appraisal with a cost approach on our flooders. You can try an alternate method of ascertaining the RCV like a hazard insurance policy. I would be wanting to change some policies and procedures if your lenders are able to forego a certified appraisal on your properties in a special flood hazard area.

Well, that does leave you in sort of a dilemma.

AMOUNT 2. What is the “insurable value” of a building and how is it used to determine the required amount of flood insurance?

The insurable value of the building may generally be the same as 100 percent Replacement Cost Value (RCV), which is the cost to replace the building with the same kind of material and construction without deduction for depreciation. In calculating the amount of insurance to require, the lender and borrower (either by themselves or in consultation with the flood insurance provider or other appropriate professional) may choose from a variety of approaches or methods to establish the insurable value. They may use an appraisal based on a cost-value (not market-value) approach, a construction-cost calculation, the insurable value used on a hazard insurance policy (recognizing that the insurable value for flood insurance purposes may differ from the coverage provided by the hazard insurance and that adjustments may be necessary), the replacement cost value listed on the flood insurance policy declarations page, or any other reasonable approach, so long as it can be supported.
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Oh just found out this is not for a new loan its an existing loan. The cabin is now in a flood zone due the map changes made in July.

You should start your force placement procedures. See Randy's FAQ posted above for RCV determination.