Optimum vent locations for partially-pressurised rainscreens

Wind tunnel measurements of pressures across a rainscreen wall are reported for a new venting scheme which seeks to achieve a “partially-pressurized” rainscreen. The concept is to vent the rainscreen compartment at the location of its maximum mean exterior pressure, thereby creating an outward-acting (negative) mean pressure across the rainscreen which opposes water infiltration everywhere. A pressure module comprising a variable number and size of vented compartments was inserted into the face of a rectangular building at the central top and side edges, corner and centre. The compartments were vented only at the edge furthest from the nearest building edge where the mean exterior pressure is most positive under most relevant situations. Mean exterior and cavity pressures were measured. The results are very promising. At the central edge locations (which receive intense wetting), the venting scheme results in all negative or near zero differential pressures on the rainscreen.