Considerable work has focused on the deterioration of jointing compounds used to seal building joints; less emphasis has been placed on understanding the consequences of seal failure, particularly in respect to watertightness. Jointing products are subjected to different climate effects; some induce aging in the sealant that in time leads to deficiencies. Deficiencies may also come about from design faults or improper installation. Water entry at deficiencies may lead to a number of different deteriorating effects on the building fabric that may induce failure of other envelope components or premature failure of the joint sealant. Joints are also subjected to substantial wind driven rain loads, in particular atop multi-story buildings. The approach taken in this study focuses on determining the fault tolerance of joint systems of a simulated wall panel when subjected to watertightness tests that emulate heightened wind-driven rain loads. Vertical and horizontal joints of 20 mm width and sealed with a one-component polyurethane product were subjected to water spray rates ranging between 1.6 and 6 L/(min-m²) and pressures of up to 2 kPa. Faults introduced to the sealed joint and representative of deficiencies through which water could penetrate consisted of cracks of 2 to 16 mm long introduced along the sealant to substrate interface. For specific crack lengths, the crack size related to the degree of joint extension, the extension reaching a maximum of 10 % of joint width. Rates of water entry across the joint were determined for cracks of different lengths and size and the nature of water entry at deficient joints in which cracks were introduced was also examined. Results on vertical joints indicated that water readily enters open cracks in relation to the crack size, quantity of water present at the crack, and pressure across the opening. Water may also penetrate cracks of nonextended “closed” joints.