Today during a heavy rain I disovered that we had a leak. We had a steady drip of water coming from the furrdown in the powder room. It only lasted about 20 minutes, but it continued to rain heavily for another hour which I thought was unusual. Not that I wanted more water in the house. We'd love some advice on how to repair/diagnose. Thank you!
Most leaks over bathrooms - even first floor bathrooms in two-story homes - are caused by one thing, and one thing only: Plumbing vent flashing.
Pipes extending through your roof are flashed using rubber gaskets, with shingles laid overtop to create a watertight seal. Constant sunlight exposure, though, can cause materials to deteriorate, allowing water to get in. Once inside, the water follows that pipe through the home, to wherever it ends - which in this case, I'd wager, is your first-floor bathroom.
Try repairing the plumbing vent flashing by sealing or replacing it and see whether the leaking stops.