Shortly after the reroofing of the lower level of an office building I own, a rainstorm occurred.Water leaked into the offices below the roof. We hadn't had leakage before. An investigation of the roof membrane, which included a flood test and spray test of the membrane and base flashings showed that the new roof membrane was not at fault. The roofer said that the leaks were coming from the masonry. When we sprayed water on the masonry wall section that extends above the lower roof level, leaks did develop. Did the reroofing process damage the masonry walls, causing them to leak?
To determine the exact cause of the leak, testing would be needed and several questions would have to be answered. What type of counterflashing was used on the new roof? What type of counterflashing existed on the old roof and how was it removed? What was the condition of the wall beneath the existing base flashing? What was the position of the existing masonry through- wall flashing? Though I can't say what caused the leak without this information, here are some of the possible reasons: The new roof base flashing may have extended up the wall farther than the original roof base flashing. This could cause the new base flashing to cover up the weep holes along the masonry through-wall flashing. In this case, any water entering the masonry would be directed behind the new roof base flashing. The existing counterflashing for the previous roof may have been bent up to install the new roof base flashing and then bent down again to cover the top of the new flashing. This may have formed a small gutter along the top edge of the counterflashing which could collect water and create leaks. If a surface-mounted counterflashing or retaining bar was used above the top edge of the new base flashing, this may be leaking. Water running down the face of the masonry could enter behind the top edge of this retaining bar, then travel behind the roof base flashing. If the existing roof base finishing extended higher up the wall than the new roof base flashing, the newly exposed masonry could be leaking. These joints may not have been tooled but simply struck because the original contractor knew they would be convered by the old base flashing. Because the old base flashing covered this wall previously, there would be no through-wall flashing to carry water out of the wall at this point.