I had just walked back up to the house this morning, for a second cup of coffee, when the phone rang. Neighbor has a roof leak. Great; 20 degrees here this morning, with a fresh light coating of snow, so where else would I want to be than on a roof?!?! So, he shows me a wall with a bathroom on each side, and water literally running down both sides. We walk outside, and sure enough, the vent stack is right where the leak is. Well, it looks okay at a distance, so let's look in the attic. Hmmm, no evidence of a flashing leak, but what's this? The insulation was all rolled out nice and straight, but I could shine my light through the gaps around the vent stack into the wall cavity. Pack the insulation around the pipe, and head back down. Put my infrared thermometer on the wall, and as I expected, a 15-20 degree drop in that particular cavity. A cup of coffee and some idle chat later, the differential was decreasing, so his assignment for this afternoon is to pick up a can of red Great Stuff, and head back up to the attic.