The external Research Program of Canada Mortgage and Housing Corporation accepted the proposal by MJM Acoustical Consultants INC. to conduct a study on the noise isolation provided by windows of residential projects. A total of eighteen tests were conducted: nine on stand-alone double glazing thermopanes and nine on different types of operational windows. The report is addressed to acousticians, builders and construction professionals; it discusses the sound isolation properties of three types of operable windows most commonly used in residential construction, and compared the performance of the windows to that of the stand-alone thermopanes tested.