According to the Insurance Institute for Business & Home Safety (IBHS), plumbing supply failures are the leading source of residential water losses-almost 50 percent greater than the second-leading source. Many of these are caused by broken pipes that result from water that gets trapped inside them and freezes.

When water freezes, it goes through a volumetric expansion of about nine percent. This is due to the hydrogen molecules bonding and forming an open hexagonal lattice structure that takes up more room than liquid water.

But it's not the ice itself that breaks the pipes. As noted by the IBHS, as the ice continues to freeze and increase in volume inside the pipe, it forces the water trapped between the ice blockage and valves (faucet) to increase in pressure to the point where the pipe fails. This is why it is often recommended to let faucets drip when freezing is anticipated-a slightly opened faucet can help dissipate excess pressure.

Ice-related pipe bursts usually are a supply line problem. Drain lines certainly can freeze but, in theory, they are supposed to be devoid of water unless they are in use. Even if they do contain water, they usually are not completely full, which means that the combination of running water and room for expansion keeps them relatively safe from freeze-related bursting. They are still susceptible to ice-related blockage and overflow, though.

Supply lines, however, usually are full. When not in use the water in these lines is static, making it susceptible to freezing. The lines also are under pressure; even a small break can mean thousands of gallons of water in places where it is not supposed to be, resulting in considerable damage.

Freezing pipes is a problem in northern portions of the U.S. during very cold weather. However, this phenomenon is not limited to a particular geographical location. In fact, houses in southern climates can be more vulnerable to frozen pipes during cold spells because of construction practices and unprepared homeowners.

Freezing pipes is a concern in southern states when temperatures begin to dip below 20 degrees Fahrenheit. Research from the IBHS indicates that this is when pipes in unconditioned attics begin to freeze. The threshold is lower in northern climates, where homes are more likely to be built with freezing temperatures in mind.

The root problem is not always freezing temperatures, however. In newer homes, the appearance of frozen pipes sometimes masks an installation defect. Construction-related defects with respect to the installation of supply lines tend to fade over time because these conditions usually make themselves apparent in the first few years of a house being built. Installation-related issues usually are found in the fittings, connections, and joints, whereas pipes can burst at any location on the pipe due to freezing. It is important for the claims investigator to answer this question: Did the pipe/fitting burst due to ice, or did it come apart due to poor installation? This might involve a closer examination of the fitting and fixtures to determine if there are workmanship issues or if a manufacturer's defect is present.

The actual cause of the event may be attributable to freezing temperatures, or a latent pre-existing condition may have been exacerbated by cold weather. A broken pipe might not always be readily visible, making the determination of the cause and age of the event less evident. Supply lines often are installed in or under concrete slab-on-grade foundations or inside walls. Detailed observations of the condition of the pipe would necessarily include removing finish materials to expose the pipe. Preferably this would be done in the presence of the claims investigator because what a contractor might discard could hold critical clues as to the age of the leak.

There are many conditions that the claims investigator might look for to determine cause. First is whether the leak is coming from a rupture in the pipe or from a pinhole leak. Rupture would be consistent with damage caused by freezing water. Pinhole leaks in a pipe, on the other hand, can result from a different mechanism and are formed in a couple ways, such as internal corrosion of the pipe due to age, hard water, or even galvanic exchange.

Further, copper pipes often are used to ground the electrical system. If a current is running through a pipe on a regular basis, pitting is a possibility as the current finds its way into the ground. Also, if the supply line runs through or in the slab and is in contact with rebar, the pipes can prematurely corrode and pit due to galvanic incompatibility.

Evidence of these conditions being ongoing and not that of a one-time, acute event would be in the form of green corrosive buildup inside the pipes (requiring destructive investigation to observe), and white or green discoloration around a pinhole. Distress to finishes and building materials that would be indicative of an ongoing issue would be discoloration of framing and finishes; blistering and delamination of finishes; recent repairs; and fungal growth in the vicinity of the leak.