Written & reviewed by Marcus ReedIICRC WRT
Reviewed September 4, 2026· Next review Mar 2027
Quick answer
Pipes don't usually burst where the ice is — they burst from PRESSURE. As an ice plug grows, it traps water between itself and the closed faucet downstream; that trapped water has nowhere to go, pressure multiplies, and the pipe splits at its weakest point, often feet from the freeze. That's also why opening a faucet to a trickle protects a vulnerable line — it relieves the pressure — and why the actual flooding usually starts at THAW, when the ice plug melts and the split opens up. If your pipe froze: keep the faucet open, warm gently from the faucet side, and be ready at the main shut-off when it thaws.
Sound like your situation? Confirm it in one call instead of ten more minutes of reading — (888) 840-6512 · toll-free · no obligation
Ice expands ~9% — but that's not what splits the pipe. The burst comes from water pressure trapped between the ice plug and a closed faucet, and the flood arrives at thaw. Here's the mechanism and the fix.
The Short Answer
Pipes don't usually burst where the ice is — they burst from PRESSURE. As an ice plug grows, it traps water between itself and the closed faucet downstream; that trapped water has nowhere to go, pressure multiplies, and the pipe splits at its weakest point, often feet from the freeze. That's also why opening a faucet to a trickle protects a vulnerable line — it relieves the pressure — and why the actual flooding usually starts at THAW, when the ice plug melts and the split opens up. If your pipe froze: keep the faucet open, warm gently from the faucet side, and be ready at the main shut-off when it thaws.
What This Page Covers
The physics of a burst pipe: ice expansion, trapped pressure, and why the split usually happens AWAY from the ice plug — plus why the flooding starts hours later at thaw, and the checklist that prevents it.
Talk to a water damage pro now
Avg 45-min response · Free call · Your ZIP routes you to the nearest crew
(888) 840-6512- Describe the damage & give your ZIP
- You're routed to the on-call local crew
- They quote — you decide, no obligation
If Water Is Still Coming In
Stop the water at the fixture valve or the main, cut power to wet rooms at the breaker if you can reach the panel safely, move what you can out of the water, and photograph everything before it is touched. Water that has reached carpet pad, drywall or a subfloor is a same-day restoration call rather than a cleanup: mold can establish on wet materials within 24–48 hours, and every hour of delay moves materials from "dry it" to "replace it."
Before You Sign Anything
Ask for a written scope and the pricing basis, who is fixing the water source and when, and what the moisture readings are — a company that does not take readings is not drying. Sudden, accidental water damage (a burst pipe, a failed supply line, an appliance leak) is usually covered by homeowners insurance; long-term leaks, neglected maintenance and rising outside water usually are not. Document first, then call the restoration company, then the insurer.
Reading to confirm what you already suspect?
Confirm it in two minutes instead — the pro on this line answers questions about YOUR situation all day: what it is, what it should cost, whether you even need service. If you want, they'll set the appointment on the same call.
Toll-free · no obligation · asking costs nothing
Frequently Asked Questions
- 1open the served faucet fully
- 2warm the suspect run gently from the faucet side back toward the plug — hair dryer, heat lamp, warm towels, never an open flame
- 3check the run for frost, bulges or hairline splits as it thaws
- 4know where the main shut-off is before the thaw finishes. If you find any split or the line weeps: main off, and a certified water damage crew on the line before the walls soak.
- 1outdoor hose bibs and the lines feeding them
- 2supply lines in unheated crawl spaces, attics and garages
- 3runs inside exterior walls — especially under kitchen and bathroom sinks on outside walls
- 4anything that froze before, because it will again. Foam sleeves, heat cable on chronic offenders, and sealing the drafts that hit them cost a fraction of one drying job.
At what temperature do pipes actually burst?
Risk starts when the air AROUND the pipe holds at about 20°F (-6°C) or lower for several hours — the research threshold the insurance industry uses.
Pipes in exterior walls, crawl spaces, attics, garages and cabinets on outside walls freeze first, because the number that matters is the pipe's micro-climate, not the thermostat.
Why does the flooding start when the pipe thaws?
The ice plug itself often SEALS the split while everything is frozen — the crack is there, but nothing flows. When the plug melts, full line pressure returns and pushes water straight out of the split.
Many homeowners report the burst 'happened' mid-morning on the warm day AFTER the cold snap; it actually happened during the freeze and announced itself at thaw.
Does leaving a faucet dripping really help?
YesFor the right reason.
The drip barely slows freezing; what it does is relieve PRESSURE, so even if an ice plug forms, the trapped water between plug and faucet can escape instead of splitting the pipe. Prioritize faucets served by lines running through unheated or exterior spaces.
My pipe is frozen but hasn't burst — what now?
Act while you're lucky:
Will insurance cover a frozen-pipe burst?
Typically yes for the sudden water damage — with a condition: insurers expect you to have maintained heat in the home (and in some policies, to have shut off water when away). The claim runs on documentation: photos at discovery, quick mitigation, and the drying log from a certified crew.
Which pipes should I protect first?
In order of burst frequency:
Sources
Methodology: How we source and verify data · Report an error
Disclaimer: HearthDry is an independent educational resource. This article is for informational purposes only and does not constitute professional, legal, or insurance advice. Consult licensed professionals before making decisions about your property or insurance claims.
Recommended Equipment
Tools Water Damage Pros Use
Remove moisture fast — needed for drying walls, floors & crawlspaces
Shop on Amazon →Professional-grade air circulation speeds drying time by 3–5x
Shop on Amazon →Detect hidden moisture behind walls & under floors before mold starts
Shop on Amazon →Smart alarms alert you the moment a leak starts — prevent next time
Shop on Amazon →As an Amazon Associate, HearthDry earns from qualifying purchases. Prices and availability may vary.
