Distribution of wind-driven rain deposition on low-rise buildings: Direct impinging raindrops versus surface runoff

• Test-based data of rain admittance factors and surface runoff coefficients were presented.
• Windward walls received higher concentration of direct impinging raindrops as compared to roofs.
• Leading edges of the building models received high volume impinging rain.
• The gable-end wall and the windward sloped ridge were exposed to high rate of impinging raindrops.
• Roof overhangs were ineffective in reducing direct impinging rain.

Wind-driven rain (WDR) effects on various components of a building facade are dependent on the total volume of rainwater deposition. The total volume of WDR deposition at a specific location on the building facade has contributions from both directly impinging raindrops and accumulated surface runoff. The distribution of WDR deposition over the building surface is dependent on the nature of the storm and on the aerodynamic shape of the building. This paper presents an experimental study conducted to investigate the distribution of WDR deposition on the external facade of low-rise buildings. Two parameters that quantify the distribution of direct impinging raindrops and surface runoff rainwater over the building surface—rain admittance factor (RAF) and surface runoff coefficient (SRC), respectively—were measured separately under simulated WDR conditions. Test-based RAF and SRC datasets were developed for three types of building models (gable, flat, and hip-roof buildings) tested for various wind directions. Test results indicated a higher concentration of direct impinging raindrop deposition on windward vertical surfaces of the building when compared to the horizontal roof components. The test results also demonstrated that the leading edge/corner regions of the buildings received less volume surface runoff rainwater, and the rainwater accumulation increases toward the leeward surfaces. The test-based RAF and SRC data developed in this work may be used for estimation of WDR deposition on façades of low-rise buildings as well as water intrusion through building envelope breaches, openings, and defects.