Yesterday for the 1st time ever I had a call in regards to a project we did. We ran a roof drain with overflow system, horizontally about 30 feet in ABS plastic material above a tee bar ceiling in a strip center. The contractor told me that during the rain it is dry, then a couple of days later it's dripping wet, while the overflow system is dry inside and out. It has been colder than usual, but we have numerous installations similar to this one with no problems, at least they don't call. I guess we will be insulating this one, normally we only insulate the first 8 feet inlet and outlet to water heaters, and all hot piping when a circulating system is installed.