Is there a good way to find a small leak when visual inspection fails? My house is from the 60s and has a second layer of shingles over the first. There is a leak somewhere in the part of the roof over the sun porch but the water seems to be running down to the lower edge underneath the top layer of shingles. It drips out inside and outside the wall at the low end of the roof. I don't know if it is runing down on top of the first layer of shingles or on top of the paper underneath. But it is not getting through both layers of shingles plus paper and dripping down onto the ceiling. It takes about 20 minutes after the start of a rain storm for water to seap down to the lower edge and start to drip. I have sucessfully patched some other visually obvious holes with roof patch. But I can't find this one. I know I need a new roof, but I want to postpone it a while longer until I am better able to afford it.