R.I. Gen. Laws § 45-24.1-7
The commission shall file with the building official or other duly delegated authority its certificate of appropriateness or rejection of all plans submitted to it for review. No work shall begin until the certificate has been filed, but, in the case of rejection the certificate is binding upon the building official or other duly delegated authority and no permit shall be issued in such a case. The failure of the commission to act within forty-five (45) days from the date of an application filed with it, unless an extension is agreed upon mutually by the applicant and the commission, is deemed to constitute approval. In the event, however, that the historic district commission makes a finding of fact that the circumstances of a particular application require further time for additional study and information than can be obtained within the period of forty-five (45) days, then the commission has a period of up to ninety (90) days within which to act upon the application.
R.I. Gen. Laws § 45-24.1-7