I am designing a brick veneer wall with metal stud backup. The gypsum sheathing over the metal stud is covered with #15 building paper. I plan to lap the building paper over the top edge of the through-wall masonry flashing. Is it necessary to seal the flashing to the sheathing, or is covering the top edge with the building paper and lapping 3 inches sufficient?
It is not necessary to seal. The building paper will direct water onto the front surface of the flashing. Sealing the flashing, however, may provide extra protection. If the building paper is not installed properly or is torn during installation, water may get behind the building paper. Sealing the top edge would help protect against leakage should this occur. Lapping the building paper 3 inches, however, may not be enough in all cases. The Brick Institute of America in Technical Notes 28B recommends using a minimum 6-inch lap.