Over the years I have seen lots of moisture issues on fireplace and chimneys, behind walls and above doors and windows. It causes mold where mortar builds up between back of brick wall and the exterior sheeting at the base of the wall first 2 feet. This has gotten to be a problem with newer houses because they have foam board for exterior sheeting not plywood or OSB. NOTE: Flashing can be a stainless 22 gauge sheet metal bent fabricated and lead soldered. Also flashing can be made of 40 mil. rubber membrane with a liquid primer you paint on first. These 3 pictures show installing a 4x6x ½ inch lintel bolted to framing installing a through the wall stainless steel flashing rubber flashing on a cantilever balcony that has leaked for many years.