Green Guard DC14 Drainage Board (PDF) is a secondary weather barrier designed with large channels that allow water trapped behind exterior walls to escape. Made of extruded polystyrene, the material's closed-cell structure doesn't absorb water and has an R-value of 1. DC14 works most effectively behind claddings that fasten tightly to the sheathing, such as fiber cement, wood, or foam-backed vinyl. 888-828-2850.