The most common masonry wall system in residential construction is brick veneer. All brick veneer walls are drainage walls. Their design should be based on the premise that water is going to enter into the wall system. Therefore, to ensure the wall's successful performance, the wall design must incorporate a means for water egress. DRAINAGE SPACE The first requirement for a brick veneer wall is a functional drainage space. If possible, design the wall system with a 1 « -to 2-inch air space. One recent innovation that can promote effective drainage is an insulated polyisocyanurate board with an integral plastic drainage panel as its exterior face. This material can be used in lieu of an airspace and standard sheathing material. FLASHING Moisture that penetrates the brick veneer and flows down the drainage space must be collected and directed back to the exterior of the building. Flashing is a membrane installed in a drainage wall that facilitates this process. Three locations in a brick veneer wall must be designed with flashing: above openings, below openings, and at the base of the wall.