I also posted this in the Plumbing section because I wasn't sure of where this goes exactly. This was discovered while working on studs and subfloor so maybe it goes here. To sum up, we are replacing subfloor upstairs and applying BIN primer in an attempt to get rid of the smell of cat urine in our home. Upon opening up the floor, we noticed that there was a white duct line which seems to be the exhaust line for our downstairs bathroom. The duct line has a tear below it and we can see what appears to be new signs of water leakage on a piece of framing. There is also a tiny sliver of blackness (1/16'' to 1/8'') on the edge of an I-joist on the wall where the exhaust line exits the house. I have pictures below. I do not believe we did anything in particular to cause this as we only removed subfloor but this was visible soon after we removed the subfloor. Not sure if it is just a coincidence and we are lucky we happened to be opening the subfloor at this time. I was wondering if we need to call in a professional to fix this or this is something easy we can repair. What alarms me is that there appears to be mildew on the exhaust line as well and I have no idea how extensive it is. damage on board where exhaust exits house at the top of the picture mildew kinda hard to see but this the tear under the line exhaust exit Thanks.