Section 21. Any public agency or limited dividend or nonprofit organization proposing to build low or moderate income housing may submit to the board of appeals, established under section twelve of chapter forty A, a single application to build such housing in lieu of separate applications to the applicable local boards. The board of appeals shall forthwith notify each such local board, as applicable, of the filing of such application by sending a copy thereof to such local boards for their recommendations and shall, within thirty days of the receipt of such application, hold a public hearing on the same. The board of appeals shall request the appearance at said hearing of such representatives of said local boards as are deemed necessary or helpful in making its decision upon such application and shall have the same power to issue permits or approvals as any local board or official who would otherwise act with respect to such application, including but not limited to the power to attach to said permit or approval conditions and requirements with respect to height, site plan, size or shape, or building materials as are consistent with the terms of this section. The board of appeals, in making its decision on said application, shall take into consideration the recommendations of the local boards and shall have the authority to use the testimony of consultants. The board of appeals shall adopt rules, not inconsistent with the purposes of this chapter, for the conduct of its business pursuant to this chapter and shall file a copy of said rules with the city or town clerk. The provisions of section eleven of chapter forty A shall apply to all such hearings. The board of appeals shall render a decision, based upon a majority vote of said board, within forty days after the termination of the public hearing and, if favorable to the applicant, shall forthwith issue a comprehensive permit or approval. If said hearing is not convened or a decision is not rendered within the time allowed, unless the time has been extended by mutual agreement between the board and the applicant, the application shall be deemed to have been allowed and the comprehensive permit or approval shall forthwith issue. Any person aggrieved by the issuance of a comprehensive permit or approval may appeal to the court as provided in section seventeen of chapter forty A.