Now I am trying to find a perminant solution. I opened the attic bedroom's wall and found that the water pipes laying on the floor of the unheated trangular area behind the wall. Because of the ventilation required, I guess the area where pipes are can get very cold. Currently there are some tapes wrapped around the pipes but not completely.
I am thinking of buying more tapes and wrap the pipes more carefully and tightly. Also, put some extra insulation on top of the pipes. Is this enough? Last winder the lowest temp was -10F here.
If not, what's a good solution of the problem.