Understanding freezing and bursting pipes

How pipes freeze and burst, and what to do to prevent damage

When water freezes, it expands. That’s why a can of soda explodes if it’s put into a freezer to chill quickly and forgotten. When water freezes in a pipe, it expands the same way. If it expands enough, the pipe bursts, water escapes, and serious damage results.

Why pipes burst

Surprisingly, ice forming in a pipe does not typically cause a break where the ice blockage occurs. It’s not the radial expansion of ice against the wall of the pipe that causes the break. Rather, following a complete ice blockage in a pipe, continued freezing and expansion inside the pipe causes

water pressure to increase downstream between the ice blockage and a closed valve or closed faucet at the end. It’s this increase in water pressure that leads to pipe failure. Usually, the pipe bursts where little or no ice has formed. Upstream from the ice blockage, the water can always retreat back towards its source, so there is no pressure buildup to cause a break.

Note: Water must freeze for ice blockages to occur, so pipes that are adequately protected along their entire length—by placement within the building’s insulation, by insulation on the pipe itself, or by heating— are safe.

Regional differences


Generally, commercial properties in northern climates are built with the water pipes located on the inside of the building insulation, which protects the pipes from subfreezing weather.

However, extremely cold weather and penetrations in the building that allow a flow of cold air to meet pipes can lead to freezing and bursting.



Water pipes in commercial buildings in southern climates often are more vulnerable to winter cold spells.

The pipes are more likely to be located in unprotected areas outside of the building insulation, and business owners tend to be less aware of freezing problems, which may occur only once or twice a season.

Pipes in attics, crawl spaces, and outside walls are all vulnerable to freezing, especially if there are cracks or openings that allow cold, outside air to flow across the pipes.

Unsealed penetrations in an outside wall can provide access for the cold air to reach pipes. The size of pipes, their composition (e.g., copper or PVC), the absence of heat, lack of pipe insulation, and exposure to a flow of subfreezing air all influence the potential for a pipe to burst.


When is it cold enough to freeze?

When should business owners be alert to the danger of freezing pipes? That depends, but in southern states and other areas where freezing weather is the exception rather than the rule (and where businesses often do not provide adequate built-in protection), the outside temperature alert threshold is 20°F. When interior pipes are left unused and exposed to this temperature for approximately 4 hours, they can freeze.

Note: Exterior pipes can freeze at higher temperatures (less than 32°F) because they are directly exposed.


Tips to prepare your business


  1. Seal exterior: Seal all cracks, holes, windows, doors, and other openings on exterior walls with caulk or insulation to prevent cold air from penetrating wall cavity.
  2. Seal interior: Insulate and seal attic penetrations such as partition walls, vents, plumbing stacks, and electric and mechanical chases.
  3. Relieve pipe pressure: For small commercial properties, let all faucets drip during extreme cold weather to prevent freezing of the water inside the pipe, and if freezing does occur, to relieve pressure buildup in the pipes between the ice blockage and the faucet.
  4. Keep the building warm: Install a monitoring system that provides notifications if the building’s temperature dips below a pre-determined number.
  5. Insulate vulnerable pipes: Pipes in attics and crawl spaces should be protected with insulation or heat. Pipe insulation is available in fiberglass or foam sleeves. Home centers and hardware stores have sleeves providing ⅛ to ⅝ inches of insulation; specialty dealers have products that provide up to 2 inches of insulation.
  6. Heating cables and tapes are effective in freeze protection. Select a heating cable with the UL label and a built-in thermostat that turns the heat on when needed (without a thermostat, the cable must be plugged in each time and might be forgotten). Follow the manufacturer’s instructions closely.
  7. Exterior pipes should be drained or enclosed in 2-inch fiberglass insulation sleeves.
  8. Pipes leading to the exterior should be shut off and drained at the start of the winter. If these exterior faucets do not have a shut-off valve inside the building, have one installed by a plumber.
  9. Install early detection system: Install an automatic excess flow valve on the main incoming domestic water line to monitor and provide early detection of a broken pipe or valve. Excessive flow valves automatically shut and stop the flow of water when preset normal flow settings are exceeded.
  10. Use wireless sensors to monitor leaks near water sources such as water tanks, commercial appliances, and the like.
  11. Install UL-approved gas or electric unit heaters in unheated sprinkler control valve/fire pump rooms.

When temporarily closing your business during the winter, be careful how much you lower the heat. A lower temperature may save on the heating bill, but there could be a disaster if a cold spell strikes and pipes that normally would be safe, freeze and burst.


  1. Adjust the temperature to a minimum of 55°F and monitor to ensure the internal temperature does not go below 40°F. Insulate pipes that enter through exterior walls to help prevent pipes from freezing and possibly rupturing.
  2. Shut off the domestic water and drain the water lines. The domestic water lines are separate from the fire protection lines. This will prevent the potential for water leaks that could result in extensive interior water damage. In cold climates, this will prevent the pipes from freezing and possibly rupturing if building heat is lost.
  3. If the domestic water lines are not shut off, inspect for leaks, and turn off the water supply line to individual fixtures such as sinks and toilets. Consider installing a monitored electronic leak detection system for the main domestic water line.
  4. Monitor fire protection sprinkler systems. Monitor sprinkler systems using a central station to provide early detection of a pipe failure and heat unheated sprinkler control rooms.


Material from the Insurance Institute for Business and Home Safety, 2021.

Insurance institute for business and home safety






The recommendation(s), advice and contents of this material are provided for informational purposes only and do not purport to address every possible legal obligation, hazard, code violation, loss potential or exception to good practice. The Hanover Insurance Company and its affiliates and subsidiaries (“The Hanover”) specifically disclaim any warranty or representation that acceptance of any recommendations or advice contained herein will make any premises, property or operation safe or in compliance with any law or regulation. Under no circumstances should this material or your acceptance of any recommendations or advice contained herein be construed as establishing the existence or availability of any insurance coverage with The Hanover. By providing this information to you, The Hanover does not assume (and specifically disclaims) any duty, undertaking or responsibility to you. The decision to accept or implement any recommendation(s) or advice contained in this material must be made by you.

LC 2021-359