Frozen copper water line shows freeze stresses (C) Daniel FriedmanMechanics & Forces of Freezing Water
Effects of ice and freezing water on building plumbing systems

  • FREEZING FORCE of ICE - CONTENTS: at what temperatures do buiding pipes burst? What is the definition of the strength or force exerted by freezing water as it forms ice; how much expansion occurs as water freezes into ice & what are the effects on building plumbing systems; how can we predict where frozen pipes will burst?
  • POST a QUESTION or READ FAQs about the force of freezing water and ice expansion in or on buildings
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This article describes the expansive force of freezing water, or the force exerted by ice as it freezes and expands. The pressure exerted by freezing water depends on temperatures and other physical conditions, but it can be tremendous - enough to lift buildings, burst pipes & plumbing fixtures, and crush the hulls of ships trapped in ice.

Here we describe the typical effects of freezing water and ice on buildings and on or in building plumbing pipes & fixtures or in appliances such as water tanks or heating boilers.

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Water Supply or Drain Pipe Freezing Mechanics - The Forces of Freezing Water

Frozen pipe burst damage pattern by joint separation (C) Daniel Friedman Temperature at which pipes freeze vs when pipes will break

As we elaborate below, while water begins to crystallize into ice at 0°C (or 32°F), its expansive forces generally do not cause water pipes to burst until temperatures further fall to around 20°F.

The actual burst point for freezing pipes has more variables including the pipe material, thickness, and even possibly its overall diameter and shape. But 20°F is a good number for the freeze point of pipes.

Does Leaving a Faucet Open Prevent Freezing Pipes from Breaking?

We know that running water, by moving warmer water from some building locations to colder pipe locations that would otherwise freeze, we can defer or even prevent frozen water supply pipes.

Watch out: at DE-WINTERIZE a BUILDING we warn that while running water may prevent supply pipes from freezing you may cause the building drain to freeze, block and even burst. Some building experts advice that when faced with freezing pipes or already-frozen water pipes we open the faucets, reasoning that if pipes are frozen you might reduce the chances of freeze-burst piping or reduce its extent by opening faucets.

Allowing even a small amount of water (from the un-frozen pipe sections) to drain out of the building supply piping might reduce some of the in-pipe pressure even if no water is flowing from the faucet. - Building Research Council (1996)

Really? While there is no question about the tremendous force of freezing water it appears to be less clear the direction in which those forces work in plumbing systems. Let's look at the force exerted on building pipes along the length of the pipe vs. across the diameter of the pipe as ice freezes.

Horizontal freezing water-forces (ice pressure) along piping lengths

An exception to our horizontal split burst frozen pipe rule that describes what we have observed most often in buildings is the occasional separation of pipes at 90 degree elbow solder joint (photo at above left). In the photo above we show that clearly horizontal forces along the pipe pushed this pipe joint apart.

But look more closely at the solder joint and you will see that the original soldering job was poorly executed without proper cleaning and use of flux. The solder was not bonded to the copper and was not uniform in the joint - this was a weak point in the piping system so it's no surprise that the pipe failed here.

Lateral water freeze-forces (ice pressure) across building piping

Frozen pipe split pattern (C) Daniel FriedmanMore often, where I observed that pipe joint separation a plumbing elbow (a common freeze point in buildings), often the elbow of bronze rather than just thin-walled copper resisted splitting while nearby softer copper piping did not.

While expanding ice inside of water supply pipes may slightly increase pressure (as water is not compressible) our field experience and photos of frozen burst pipe such as the photographs at immediate left and again at below left suggest that most often frozen water pipes burst or split from the expanding ice pressure within a small section of pipe, creating first a bulge and then a split from forces across the diameter of the pipe rather than along its length.

It certainly appears from physical evidence that the water pipe shown in my photo bulged and then split by forces across the diameter of the pipe.

A rational view is that freezing water applies force in all directions rather uniformly. But the damage done by that force occurs where the force is confined. But freezing water appears to be immediately confined more by the circumference of a pipe than along its length. Why might this be? Perhaps because the expansive force of ice increases as the temperature of the freeing water drops. A plug of ice forms in the pipe, the continues to expand as temperatures drop.

Why then might forces across the pipe be more confined than forces along the water pipe? We are not sure we not agree with one building expert who opines that the fill valve on toilets allows water, pushed along by freezing ice, to enter toilet tanks.

Really? Building water pressure varies over a range all the time for a variety of reasons (faucets open and shut, pumps starting and stopping) without ever pushing water through a closed toilet tank fill valve.

But there are building components that can absorb increasing water pressure:

  • The water pressure tank in buildings served by a private well or by a water pressure booster pump and tank system includes a compressible air reservoir
  • Cyclic water-consuming building fixtures and appliances such as water heaters, boilers, steam boilers cyclically permit water to pass through water feed valves or pressure reducing valves into the appliance or fixture
  • Leaking, dripping faucets and running toilets constantly relieve building water pressure (but sadly these conditions can cause a freeze blockage in a building drain)

What is the Expansive Force of Freezing Water?

Frozen copper water line shows freeze stresses (C) Daniel FriedmanHow much does water expand or contract as a function of temperature and how much does ice expand? Various sources give different expansion forces for freezing ice.

Depending on its state, freezing water (or ice as temperatures continue to drop) can expand by as much as nine percent at a maximum force between about 25,000 and 114,000 psi.

Actually water reaches its maximum density above freezing, at about 4°C. It is the expansion of ice as it continues to freeze that explains why icebergs float - the iceberg displaces a volume of water that weighs more than the (expanded) ice itself. The tip of an iceberg seen above water usually represents about 8% of the iceberg's total volume.

Stated another way we can explain why ice is lighter than water by explaining its expansion as water changes from liquid to frozen state.

As ice freezes forming hexagonal crystals (comprised of two H molecules join with an O molecule at an angle of 104°) the water in this form takes up more space than liquid water.

But the crystals formed by freezing water take on varying forms (and affecting the pressures exerted by confined ice) as temperatures continue to fall. - Debenedetti (2003)

Before modern physicists and engineers began calculating the expansive force of freezing water, Florentine academics had measured the strength of freezing water by enclosing water in a brass globe of known thickness and strength, then allowing it to freeze. Those academics observed that a one-inch globe of water, when freezing, could exert a 27,000 pound force. - Platts (1880)

Luckily copper plumbing has some bending or flexing ability and does not break immediately. Copper water supply pipe strength varies by pipe type and wall thickness (K, L, or M copper) but break at around 3000 psi.

The thermal expansion of water is detailed

Expanding ice forces are very strong when confined. Entire building movement caused by freezing and ice are discussed at FOUNDATION DAMAGE by ICE LENSING


Watch out: while some experts advise leaving faucets open or dripping to avoid freezing pipes, this advice is risky if the building drains are exposed to freezing. In many areas the building main drain exits above the frost line and can be exposed to very cold conditions.

During normal plumbing use the surge of wastewater down the drain makes it past this cold spot without freezing. But a dripping faucet or running toilet, sending a small but continuous trickle of water down the drain can accumulate as ice until it expands, blocks the drain (leading to a sewage backup in the building) or until the drain line freezes and breaks.

Frost-Pushed-Up Sewer Piping - Cause & Prevention of Frost Heave Damage

Reader Question:

4/16/14 Anonymous said:

How do I prevent the frost from pushing my toilet drain pipe up through the floor and dislodging the toilet from the flange on the floor. This is at a cottage.


Anon, you ask an important question, for which, with apology, I have to speculate a bit to try to answer.

Normally the toilet waste line doesn't push up through a floor.

To fix your frost-heaved waste piping we need to know why it's happening. I speculate that

  • water is running beneath your cottage floor slab - which means we need to fix that cause outside by fixing roof drainage, surface drainage, subsurface drainage, foundation drainage - otherwise there is real risk of frost damage to the structure itself.
  • the slab is probably not below the frost line - which is something one might have to live with but to do so we need to keep water out.

A "band aid" approach that I don't like is chopping out a section of flooring and packing foam insulation around the drain line in the fantasy that we can protect it from frost heaves. We need to either install construction components below the frost line or keep water out from below the foundation and slab.

  • There could be a more subtle problem pushing up the waste pipe, such as ice lensing - a topic we explain
    at FOUNDATION DAMAGE by ICE LENSING but that's not where I'd start.

Instead, start outside looking at where and how water is saturating the ground under your foundation and slab. While you're at it, and since this is a cottage that perhaps is not occupied and heated all year, also take a look


Continue reading at HEAT SOURCES to AVOID FROZEN PIPES or select a topic from the More Reading links shown below.

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FREEZING FORCE of ICE at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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