Yeah, intellectually I know that a roof collapse is unlikely, although the pitch on mine is shallow enough that I can't quite completely convince myself of that. But it had never occurred to me that I'd get an ice dam in that location, and indeed I don't know *why* it has dammed so badly there, but going out and looking, the damned thing's close to a foot thick, right at the corner of the house.

Useful food for thought on the roof; thanks. I'm probably due for re-roofing sometime in the next few years anyway, so I'll keep that in mind...