Concerns about a pipe that keeps freezing

Question

I recently purchased my first home, so I’m new to home ownership, please bear with me.

I live in the Chicago area and this winter has been particularly cold. When the weather dips below 0 degrees F, one of the pipes freezes. This pipe must be somewhat insulated as it doesn’t freeze until well below freezing temperature. It’s strange because the toilet, which I’d assume feeds off of the same water line keeps working, but the cold water line on the sink faucet stops (the hot water line is also fine). As soon as the weather heats up to about 10 degrees F the pipe thaws and everything goes back to normal.

I understand that I eventually need to track down the root cause of this issue, which I plan on doing when it’s a little warmer, but my immediate concern is regarding the best way to deal with the frozen pipe. I’m not particularly worried about not having cold water, I can temporarily use the other bathroom in the house, but I’m seeking advice on how to ensure the pipe doesn’t break and other miscellaneous concerns.

I have been keeping the cold water line open to drip, but it seems to freeze even when I do that.

A few general questions:

1. Should I keep the cold water line open to at least reduce pressure in the pipes, even if this doesn’t prevent freezing?

2. When I leave for work for the day, should I shut main water line off to prevent flooding if the pipe does break? Anything I should know about turning off the main water supply somewhat frequently until I get this resolved? Is this a bad thing to do? Do I need to do anything with the water heater when I shut the main line off? Any other advice here?

3. Regarding a more long term solution, any advice on tracking down the problematic pipe? The pipe must be in a wall that’s facing the outside of the house with little insulation. Am I going to have to rip off drywall to find the pipe?

A side note. I recently removed the sink to replace with a new one, so I currently can’t keep the cold water line open, as it has no where to drain. Any advice given this twist?

Edit: I have copper pipes. This house was built in 1978. The sink in on an interior wall but that wall backs up to an attic.

Thanks!

Answer 1

A simple way avoid freezing is keeping the tap little open (I'd say gallon per hour), because moving water won't freeze.

Another way is to use a 'heated' insulator, so if the temperature drops beyond a threshold, electric heater kicks in keeping the water few degree above freezing point.

Closing the main valve when you go it's not a good thing to do (if you don't empty the cold water piping) because you remove a secondary 'pressure relief'.

Good thing can be emptying only that trunk of pipe that freezes and preventing water passing through it.

Answer 2

An option is to find the cold-vulnerable pipe (hint: attic) and wrap it with quality heat tape, then wrap that with pipe insulation.

By "quality" I mean not the dreck sold in overpriced kits at the hardware store. I mean the good stuff, which is self-regulating heat cable sold at industrial supply like McMaster-Carr. This stuff has a resistive material whose resistance goes up quite a lot with temperature, so it reduces power when your pipe is out of the danger zone. This is not to save money but to keep the water in your pipe from overheating. Nonethless it is not made to run all year and should be shut off during the off season. Believe me, it's expensive enough, but it's the right stuff for the job.