Water Infiltration through Openings in a Vertical Plane Under Static and Dynamic Pressure Conditions

Moisture is the cause of many building deterioration problems, and rain is the prevalent source of moisture to building envelopes. Little information has to date been published on the mechanisms of water infiltration through openings in facades that also includes quantitative information to help demonstrate infiltration phenomena. A better understanding of the mechanisms that govern water entry through openings present on vertical surfaces such as cladding will lead to improvement in watertightness performance of building components, provide enhanced knowledge of boundary conditions needed to complete hygrothermal simulations, and render a more scientific approach to the design watertightness test protocols. In this paper, a quantification of the driving forces is offered and qualitative analyses of interacting phenomena is presented that help characterize water ingress through openings in facades. Experimental research was done on two types of openings in a vertical polycarbonate plate similar in configuration to deficiencies on exterior cladding: round holes (1 mm, 4 mm and 8 mm diameter), and three slits (2 mm wide, under different angles). These deficiencies made in the plate had dimensions calculated to cover a range of capillary pressures and these were subjected to a simulated wind driven rain by means of pressure differences and water spray. Pressure differences of 0, 200, 400, 600 and 800 Pa were applied, in combination with typical water spray rates used in test protocols (2.0 L/min.-m² and 3.4 L/min.-m²).

The driving forces for water ingress are gravity, pressure differences, kinetic energy of film flow, capillary action and the surface tension of the meniscus. The capillary pressure at a specific temperature is mainly determined by the dimensions of the deficiencies and the contact angle of water on the substrate. The results of the experiments clearly indicated that the capillary pressure introduced a threshold for water ingress: water entry rates were predominantly defined by the geometry of the deficiencies in relation to the contact angle. Furthermore, the surface tension of the meniscus on the interior side of the front plate defines a pressure threshold that strongly affects the way water may infiltrate through openings; and it offers interesting insights in the effect of static and dynamic boundary conditions on infiltration rates.