Requirements for chimney exterior

[Craig Hartwick]

I'm selling a rental property we've owned for over 20 years.   We have a a signed purchase agreement, but the bank is asking for sheathing on the exterior of the chimney.  The exterior of the chimney is concrete block.  Anyone know if siding, brick or stucco is required on the exterior of a chimney in Indiana?   If so, what's the cheapest exterior, stucco?

Thank you!