Wind-driven rain (WDR) intrusion through building envelope defects and breaches is a major source of damage to building interior components and contents during hurricane landfall. The extent of total building interior damage (damage to building interior components, utility, and contents) is a function of the total volume of WDR intrusion which in turn is dependent on the size of openings, wind speed, and rain intensity. Currently, the volume of rainwater intrusion through a given opening on a building façade is estimated using a semiempirical model with use of parametric information based on engineering judgment. This paper presents a test-based WDR intrusion model which uses values of parameters developed through testing of building models under simulated WDR conditions. The model estimates the total volume of rainwater intrusion through an opening as a summation of WDR volume attributable to direct impinging raindrops and surface runoff rainwater from the undamaged envelope area. Test-based WDR intrusion data measured using a building model with simulated envelope defects and breaches were used to validate the applicability of the new WDR intrusion model to full-scale buildings. Comparison between model estimation results and WDR intrusion measurements through simulated window sill cracks and envelope breaches demonstrated reasonable agreement. The model presented herein can be used to predict the WDR intrusion and subsequent interior damage to low-rise buildings during tropical storms and hurricanes.