| The study seeks to help resolve the costly problem of rain penetration of walls that plagues the building industry. An experimental study was undertaken to increase the understanding of two primary external factors affecting the design of cladding against wind-driven rain. The first is the deposition of rain on a building face; the second is the spatial nonuniformity of exterior pressures on the face.; A new method for simulating wind-driven rain was achieved using an array of nozzles in a boundary layer wind tunnel and Froude scaling. Rain impact patterns on simple buildings were simulated using a water-sensitive paper that changed colour on contact with water. This allowed a visual picture of the impact pattern and quantification of local intensity factors. The approach permits an approximate simple solution to a complex problem. The “classic” full-scale wetting pattern was obtained on windward faces whereby the edges are the wettest. Changes in wind speed, direction, aspect ratio and architectural features were examined. Local intensity factors increase significantly with wind speed. Glancing winds still result in significant impact at some edges.; A pressure-equalized rainscreen wall relies on cavity space compartmentalization to limit the external pressure change across the cavity. The intent is to reduce the differential pressure across the rainscreen to a level acceptable against water entry. However, recommendations for compartmentalization are few. To this end, a wind tunnel study of pressure gradients was conducted using a rectangular building form pressure model. Normalized mean horizontal and vertical components of spatial pressure gradients of up to 16 near side edges and 34 near the top edge, respectively, were obtained (96 and 136 Pa/m for a 40m wide, 60m high face with wind speed 20 m/s). Unsteady gradients were studied using proper orthogonal decomposition and quasi-steady analysis. Results indicate differential pressures cannot be adequately reduced at building edges using practical compartment sizes. The coincidence at building edges of maximum rain impact with high pressure gradients gives rise to a new idea, the “partially-pressurized” rainscreen, whereby an outward-acting mean pressure differential is created to oppose water infiltration everywhere. A new venting and compartmentalization scheme is suggested. |
