I assumed the leak was coming from the older portion of the roof and went to work stripping off the damaged roofing, removed the siding and step shingles and worked my way down toward the gutters. The roof had been installed over an older roof that was really in bad shape. It made it very difficult to see clearly where the roof was leaking. I removed a 3 ft. wide path of roofing and found some rot at the gutter and replaced a couple of boards.The owner told me he had purchased the house about a year ago and a roofer had done some repairs and given him a roof certification.
Next I glued down some 30 lb. felt with asphalt emulsion and started weaving in the new shingles and new step flashing working my way up the wall toward the valley. When I got to the valley, as added insurance against leaks, I put asphalt emulsion under every shingle. I felt pretty confident that the roof would be impervious to leaks; at least in this area. It was time to clean up, load up my ladders and tools and call it a day. It was perfect timing, because it was starting to sprinkle. It rained hard for two days and then my phone rang.
Bummer, the closet still had water coming in. I dropped what I was working on and jumped in my truck to go over and check it out. I really hate it when things like this happen. Sure enough the plywood under the carpet was wet.
I went up in the attic to see if I could see exactly where the leak was and it appeared to be coming in from the sidewall, just up from where I had done all of my repairs. I picked up some insulation to see how wet things might be and the whole area underneath, looked like a pile of sawdust or dirt. I poked at it and the pile began wiggling and moving. Ants swarmed out and began repairing the damage to their nest. I broke the bad news to the owner, and let him know I would return the next morning.
The next day I went up on the roof and made more repairs, this time replacing the roofing and flashing that I had assumed to be good. I found a missing piece of step flashing 6" above where I had stopped two days before. The lesson for me is to never assume that a previous repair was done correctly. Attending Hard Knocks University is never fun and a few hours of warranty work, doesn't help pay the bills.
I next removed the siding below the roof line to figure out where all of these ants were coming from. The siding was old and brittle, so it was tedious and careful work.