I have always enjoyed a treasure hunt which, if you are successful, there is a prize at the end. Finding the source of water damage is a lot like a treasure hunt and, at the end I have helped my customer protect his asset.
Water and gravity will always work together. Sometimes it feels like they like to play tricks on us. Rule of thumb: water can and will go anywhere gravity might take it so your roof must be water tight.
A nice lady once called to get our help on a leak she kept having the north side of the garage. She had the garage roof checked but could find no problems. The shingles looked good but still it would leak — mostly when it was cold out and it snowed.
So we first checked the roof shingles...nothing
Then the flashing...nothing
Thirdly, we checked the venting....nothing
Next a water test for the garage roof....no water leaked.
Well what could it be?
What's behind the wall? Electrical cords, ducks and pipes.
The pipes go over to the south a little...
then up to the first floor...
going into the closet...
second floor now, in this wall...
follow them over and up some more...
Wow clear up to the third floor and then where?
can't find them ...
oh there they are...
going up into the attic...
The pipes go out of the roof.
We look at the water stains on the elbows of the pipes.
The third floor south side of the home roof is leaking, all the way down three stories to the north side of the garage wall.
Well we can fix that.
Gravity works in strange ways.