[zbwmy]

Bath tub drain of second floor bathroom froze in our 1 deg. winter today.
Drain pipe travels down outside wall into basement. Is there a small clog somewhere that would allow water to pool so it could freeze? I cant't see running water freeze in a 2 in. pipe. What do you think about spraying GREAT STUFF into floor cavity where pipe enters wall in basement? Should I just wrap exposed pipe in fiberglass?

 

[PipeGuy]

Sometimes sealing around a pipe like that will worsen the situation - whatever heat was getting into the wall cavity is now sealed out. Same goes for insulation. You're right that it's unusual for a 2" drain pipe to freeze. There's probably a clog building that has been exacerbated by freezing. Liquid plumber might generate some heat and open it up. However you do it, it sounds like you have an obstruction that needs to be addressed.

 

[zbwmy]

Sometimes sealing around a pipe like that will worsen the situation - whatever heat was getting into the wall cavity is now sealed out. Same goes for insulation. You're right that it's unusual for a 2" drain pipe to freeze. There's probably a clog building that has been exacerbated by freezing. Liquid plumber might generate some heat and open it up. However you do it, it sounds like you have an obstruction that needs to be addressed.

I should have mentioned that applying hair drier heat to that basement elbow drained the tub.