My home is about 50 years old, and the insulation along the underside of the roof in the attic has pulled away from the staples holding it to the rafters and fallen down in several places. I had been replacing the insulation between the rafters where it has fallen with new insulation, until I came upon a wet spot on the underside of the roof. It was frozen when I first noticed it, as this was during the winter and I had snow on my roof at the time. My first thought was that I have a leak in the roof and might have to replace my whole roof. I stopped the insulation project to monitor this wet area. The spot dried as spring came and melted the snow from the roof. I continued to monitor the area through heavy rain storms, and it remained dry thoughout last summer. When the first snow and ice storm struck late last autumn/early winter, I noticed that this same area about the size of a small football and 3 feet up from the eaves had returned, much to my dismay. It again dried up within days and the snow melted from the roof. The wet spot did not return the rest of the winter, even though we had additional snow and rain. My dilemma is this; I am left to wonder whether or not I do need to replace my roofing shingles, since the area is not consistently wet. With the exception of these 2 instances spaced 6 months or so apart, it remains dry for extended periods of time during the course of heavy rain and snow. This gives me hope that there may not be a leak, and that on the 2 occasions I have noticed moisture, I am wondering whether it was not just condensation forming from warmer air in the attic meeting the colder surface of the snow laden roof. Should I resume installing new insulation over the previously wet area now that it is dry and summer is here,(figuring that insulation will form a vapor barrier to prevent moisture from again forming), or do you suspect a much greater problem that may require new roofing shingles be installed? I have been hesitant to continue with the insulation project, not wanting to mask a bigger problem. What should I do??? The current roof is only about 15 years old and appears to be in good condition from the outside.