Section 11. Meetings of a commission shall be held at the call of the chairman and shall be called at the request of two members of the commission and in such other manner as the commission shall determine in its rules. A majority of the members of a commission shall constitute a quorum. The concurring vote of a majority of the members of the commission shall be necessary to issue a certificate of appropriateness, a certificate of non-applicability or a certificate of hardship.

A commission shall determine promptly, and in all events within fourteen days after the filing of an application for a certificate of appropriateness, a certificate of non-applicability or a certificate of hardship, as the case may be, whether the application involves any exterior architectural features which are subject to approval by the commission. If a commission determines that such application involves any such features which are subject to approval by the commission the commission shall hold a public hearing on such application unless such hearing is dispensed with as hereinafter provided.

The commission shall fix a reasonable time for the hearing on any application and shall give public notice of the time, place and purposes thereof at least fourteen days before said hearing in such manner as it may determine, and by mailing, postage prepaid, a copy of said notice to the applicant, to the owners of all adjoining property and other property deemed by the commission to be materially affected thereby as they appear on the most recent real estate tax list of the board of assessors, to the planning board of the city or town, to any person filing written request for notice of hearings, such request to be renewed yearly in December, and to such other persons as the commission shall deem entitled to notice.

As soon as convenient after such public hearing but in any event within sixty days after the filing of the application, or such lesser period as the ordinance or by-law may provide, or within such further time as the applicant may allow in writing, the commission shall make a determination on the application. If the commission shall fail to make a determination within such period of time the commission shall thereupon issue a certificate of hardship.

A public hearing on an application need not be held if such hearing is waived in writing by all persons entitled to notice thereof. In addition, a public hearing on an application may be waived by the commission if the commission determines that the exterior architectural feature involved or its category or color, as the case may be, is so insubstantial in its effect on the historic district that it may be reviewed by the commission without public hearing on the application, provided, however, that if the commission dispenses with a public hearing on an application notice of the application shall be given to the owners of all adjoining property and other property deemed by the commission to be materially affected thereby as above provided and ten days shall elapse after the mailing of such notice before the commission may act upon such application.