reply to alkizmo
Re: EXTREME freezing temperatures - What to worry about? Keep watch on that bathroom with the frozen pipe. What's frozen now could become a problem when the ice thaws... If the pipe has a split then you'll have a real mess when the water turns to liquid again.
I've always done the "open cabinet" trick for all sinks that are on outside walls and be sure to leave BOTH the cold and hot water trickling a bit so the water in both pipes is constantly moving. At those temps you may need to leave a fairly decent stream running to prevent freezing up.