Wetting, in particular rain wetting, of walls with a masonry veneer is an important performance consideration for reasons of aesthetics, durability, and utility. Over the past four years, a variety of full-scale clay brick veneer wall systems have been tested in the BEGHUT field test facility. These long-term investigations of the response of wall systems to the southwestern Ontario climate have involved observation of both the exterior and interior environments as well as the performance of the brick veneer. Standard and non-standard air and rain penetration testing has been conducted. Temperature, vapor pressure, air pressures, and brickwork moisture content have been measured. The contribution of vents of various kinds and the flow characteristics (both air and water) of the region behind the screen has been studied. In the latest project, two weather stations are used to monitor the sun, wind, rain, and driving rain. There are also 14 driving rain gauges mounted on the walls of the facility. The objective of this paper is to propose a probabilistic model relating the wind, rain, and rain penetration. Driving rain, wetting, and surface drainage are discussed in some detail. Some of the more significant preliminary results of this research and its application to wall performance and rain penetration testing, especially for brick veneers, are presented and discussed.