Section 18A. A savings bank or co-operative bank incorporated in this commonwealth, subject to such regulations as the commissioner of banks deems necessary or advisable, may, either alone or in conjunction with one or more other savings banks, co-operative banks, or savings banks and co-operative banks undertake one or more projects under this chapter or acquire projects or any severable portion thereof from corporations authorized to undertake projects under this chapter. The provisions of section eighteen and section eighteen B shall, so far as apt, be applicable to such bank or banks, except that the board of investment of a savings bank and the security committee of a co-operative bank shall have the powers and duties granted to or imposed upon directors of an insurance company under said section.

No investment shall be made by a savings bank or co-operative bank under this section if thereby the total amount invested by such bank pursuant to this section would exceed three per cent of the deposits of such bank. In addition to any other investment authorized by this section, any bank undertaking such a project, alone or in conjunction with one or more other banks, may make, or participate with one or more institutions in the making of a loan or loans secured by a first mortgage upon real estate located within such project. For the purposes of this section a loan by any such bank secured by a leasehold under a lease of any portion of any such project, including air rights, which does not expire for at least ten years beyond the maturity date of the loan, shall be deemed a loan secured by a first mortgage upon real estate. Any loan authorized under this section shall otherwise be subject to the applicable provisions of chapter one hundred and sixty-seven E, except that in the case of a loan secured by a leasehold interest, any provisions of said chapter inconsistent with the nature of such loan shall not apply. Mortgage loans shall not be subject to, nor the amount thereof included in determining compliance with, the foregoing limitation of the amount which may be invested under this section; however, the aggregate amount invested by a bank in mortgage loans described in this section shall not exceed ten per cent of the deposits of the bank.

After a project proposed to be undertaken by a bank or banks under this section has been authorized and approved, such bank or banks may associate to form a corporation, unincorporated association, joint venture, partnership, limited partnership or trust, for the purpose of undertaking and carrying out the project, or any portion thereof, on behalf of such bank or banks and any such entity so formed shall be deemed to be an instrumentality of the commonwealth, to be exempt from taxation, betterments, excises and special assessments and to have all the powers granted and be subject to all the obligations and duties imposed under this chapter to the same extent as provided for a bank or banks undertaking a project under this section.