I was visiting Knoxville TN in early Jan 85 when they broke their all time record low temp. It was something like 18 below.
That was the year my neighbor's pipes froze - they were away and left the thermostat at 60 - but the temp under the house was lower - I think it was in the low teens. No damage in the house, thankfully.
The plumbers were so busy that we just turned their water off until they were due home, and had the plumbers come the day before to fix the pipes.