What should be done before a cold snap to lower the risk?
Heat and insulate the lines that run through cold spaces, let a faucet drip on the coldest nights where the line is exposed, and know where the main valve is before the first freeze.
A pipe that runs through an exterior wall or an unheated space is the one most at risk. Insulating the line with a foam sleeve and sealing the gap where the pipe enters the wall are inexpensive steps, and the homeowner can do them without a contractor. Opening the cabinet doors under the sink on a cold night lets room heat reach the supply line behind them.
Find the main shut-off and the branch valves before the cold comes. A valve that has not been turned in years may not close, and a stuck valve found during a leak is a bad time to learn that. The shut-off should be marked and the handle should turn freely.
Why do pipes split on the thaw and not during the freeze?
The water is trapped in the frozen section until the ice melts, and the pressure builds behind the ice. The split often opens when the line warms and water begins to move through the damaged section.
A frozen line may show no leak at all while the ice holds, and the homeowner may see nothing until the thaw. Once the water moves again, the split releases the water that was trapped behind the ice, and the flow can be strong enough to soak a room within minutes.
This is why a cold snap followed by a warm day is a common time for calls. The thaw releases the water, and the homeowner hears it running in a wall or sees a stain on the ceiling for the first time.
Who repairs the pipe, and who dries the house?
The repair of the line is done by a licensed plumber. The drying of the wall, the floor and the framing is done by the water-damage company, and the two work in sequence on the same job.
The plumber is the person who should decide how the broken section is replaced, and that work should be done with the water shut off. The water-damage crew can advise on where the line runs, using the moisture readings, but it does not repair the line itself.
Ask the plumber for the permit, the work order and the invoice, and keep them with the water-damage record. The permit questions for a repair are answered by the local building department, which is the office to call if the work involves a new run of pipe.
What should a homeowner do after a burst pipe is dry?
Check the repaired section after several days, watch the floor and the wall at the repair, and keep a note of the temperatures during the next cold snap.
Look at the repaired wall and the floor at the bottom plate for a week or two. A new stain, a soft patch or a musty smell at the repair means moisture remains, and the drying should be checked again.
Note which lines froze during the cold snap. Those are the lines to insulate or heat before the next winter, and the homeowner can use the same list each year.