Testing rainscreen wall and window systems: the cavity excitation method.

The rainscreen principle is not new. It was proposed as early as the mid sixties by researchers of the Division of Building Research of the National Research Council of Canada and the basic principles were developed. It has been applied to certain exterior wall types but the performance of rainscreen walls remains largely unknown because of the absence of engineering data. It is only recently that interest has grown in the application of the rainscreen principle because face sealing and the drained cavity approach do not allow for the satisfactory control of moisture in construction cavities from rain or from condensation. The rainscreen principle is well developed qualitatively but not quantitatively. There are no technical or engineering criteria to assist designers and few established prescriptions for the builder. The actual field performance of the rainscreen with respect to rain control is unknown and the relation to pressure equalization is also unknown. The Canada Mortgage and Housing Corporation (CMHC) recognized the need to undertake further research into the engineering and technology of the rainscreen principle. This project was commissioned by CMHC and Public Works Government Services Canada (PWGSC) to further advance the application of the rainscreen principle to exterior wall design and construction of both residential and commercial buildings. This project included three distinct areas of interest. First, the development of a method to monitor the performance of existing rainscreen wall systems and to gain insight into the actual field pressure equalization performance. This work was also coupled to a laboratory investigation of the wetting and drying of a rainscreen cavity in a metal and glass curtain wall. Secondly, the development of a field performance and design compliance testing procedure. The procedure is termed the Cavity Excitation Method or CEM. It is a field test that does not require elaborate preparations and substantial mockup facilities. Third, the development of performance criteria for the design of rainscreen systems and the development of commissioning guidelines for rainscreen wall system. This is the 2nd report of this project on rainscreen performance research. It involves both laboratory development and field testing of a new rainscreen testing procedure termed the Cavity Excitation Method (CEM). The laboratory work was undertaken in the construction laboratory of the Engineering Department of Queens University. The field work involved a building in Montreal, Quebec, "Le Clos St-Andre".