bill wrote:
whats the cause? just noticed my neighbor's roof. water is running
from the base of the chimney. outside temp is 30, its a hot air gas
fired furnace, in Maryland. i didnt notice this on other roofs.
ideas?

Rain or snow there recently? Perhaps there's a hollow spot someplace
trapping moisture that's now melting.

Sounds like something worth mentioning and investigating as could be
indicative of a chimney problem that might affect draft and hence
perhaps lead to high CO inside at worse end or roof or other structural
damage at the lesser....then again, it just might be from designed-in
weeps doing their job for external drainage if it's a masonry chimney.