If the library occupies a public building upon a site acquired therefor and the building and site are free from any bonded indebtedness, then an amount not to exceed 20% of any annual budget prepared, published and approved by the board may be allocated to a special accruing fund for the cost of erecting and equipping any addition to, or branch of, such library and for the acquisition of any additional site required for the erection of any such addition, branch or parking facility for use by the patrons of such library. Expenses for major capital improvements or major equipment purchases to cover such matters as, but not limited to, major roof repair, new computerized circulation or security systems and bookmobile replacement also may be paid with funds from the special accruing fund.