Question: I am adding a masonry veneer wall to an existing building. Because of site constraints, I can't provide the full 2-inch air space recommended by the Brick Institute of America (BIA). What can I do to assure proper drainage in an air space smaller than 2 inches?

Photo Credit: Wiss, Janey,
Elstner Associates Inc.

BIA recommends the 2-inch air space so that the masonry contractor can keep it reasonably clear of mortar droppings. If site constraints don't permit this, you might try using a prefabricated drainage mat instead. These drainage mats typically are used against foundation walls in place of gravel backfilling to permit groundwater to drain to the drain tile at the footing. Using such a drainage mat in a masonry wall can provide a small cavity space that can't be bridged by mortar droppings. Face the filter fabric side of the drainage mat toward the new masonry veneer to prevent mortar from squeezing into the mat.