The assent of the electors shall be required in all school districts of the second, third and fourth class, to issue bonds which will incur any new debt or increase the indebtedness to an amount in excess of five (5) per centum of the assessed valuation of property taxable for school purposes therein. The assent of the electors shall be required in school districts of the first class and first class A to issue bonds which will incur any new debt or increase the indebtedness to an amount in excess of five (5) per centum of the assessed valuation of property taxable for school purposes therein. The board of school directors of any school district of the first, first class A, second, third, or fourth class shall have authority, without the assent of the electors, to issue bonds which will incur upon its own authority any amount of such indebtedness not in excess of five (5) per centum of the last assessed valuation of property taxable for school purposes therein.

If the amount of bonds of any bond issue maturing in any single year is in excess of five percent of the total amount of such bond issue, the amount in excess of five percent of such bond issue may be refunded by the board of school directors of any school district, upon its own authority, without submitting any such refunding bond issue to a vote of the electors.

Any school district which calls bonds for payment prior to the date of maturity may issue bonds for the purpose of paying any or all such bonds as may be called for payment. All bonds issued for the purpose of refunding bonds shall be issued as hereinbefore provided for the issuing of such bonds.