I heard that the minimum width of the cavity in a masonry cavity wall should be 2 inches. If the cavity is insulated, is the insulation thickness considered a part of this 2 inches or in addition to it?
The Brick Institute of America (BIA), in its Technical Note 21A on insulated brick masonry cavity walls, allows rigid insulation to occupy 1/2 of the 2-inch minimum cavity width. Therefore, an insulated cavity wall would have a l-inch free-draining cavity. However, if the backup wall and insulation are installed before the brick veneer, I recommend a minimum 2-inch air space in addition to the insulation thickness. A 2-inch cavity is much easier to keep clean of mortar droppings than a 1-inch cavity.