W. Va. Code § 13-1-15

Bonds shall be made payable in annual or semiannual installments beginning not more than three years after the date thereof and the amount payable in each year may be so fixed that when the annual interest is added to the principal amount to be paid, the total amount payable in each year in which part of the principal is payable shall be as nearly equal as practicable. Once principal payments commence, it shall be an immaterial variance if the difference between the largest and smallest amounts of principal and interest payable annually or semiannually during the term of the bonds shall not exceed five percent of the total authorized issue. Bonds may be payable in annual or semiannual installments beginning not more than three years after the date thereof, each installment being as nearly equal in principal amount as practicable.