Iowa Code § 419.7
The proceeds from the sale of any bonds, issued under authority of this chapter, shall be applied only for the purpose for which the bonds were issued and if, for any reason, any portion of such proceeds shall not be needed for the purpose for which the bonds were issued, such unneeded portion of said proceeds shall be applied to the payment of the principal or the interest on said bonds. The cost of any project shall be deemed to include the actual cost of acquiring a site or the cost of the construction of any part of a project which may be constructed including architects' and engineers' fees, the purchase price of any part of a project that may be acquired by purchase, all expenses in connection with the authorization, sale and issuance of the bonds to finance such acquisition, an amount to be held as a bond reserve fund, and the interest on such bonds for a reasonable time prior to construction, during construction and for not exceeding six months after completion of construction.
Iowa Code § 419.7