Section 21. All cases in the housing court department, including motions and the like, whether interlocutory or final, shall be heard and determined by a justice of a division of the housing court department sitting without jury, except that in all cases where a jury trial is required by the constitution of the commonwealth or of the United States and the defendant has not waived his rights to a trial by jury, the cause shall be forthwith tried in a division of the housing court department before a jury selected in accordance with chapter two hundred and thirty-four. In the trial of any complaint or action in the housing court department, the report of any inspector serving in the housing inspection department of a city or the board of health of any city or town shall be prima facie evidence of the facts stated therein.