You can't rely on the professionals anymore.
In my S&B house, I had a water leak in the attic that was sporadic. It took me forever to track it down.
When the house was built, the plumber who put in the plumbing vents failed to glue one of the vent connections. When it rained, rain would fall in the 1.5" vent and run down to the unglued connection, where it would drip out. However, it did not do that EVERY time it rained. It only did it when it rained REAL HARD. A moderate rain didn't put enough water in the vent. When I finally found the problem, I glued the joint, but I also put vent covers over all of the roof vents on the house. I can't trust any of the vents to be properly glued. Since putting vent caps on, no more problems.