What leads to pipes bursting when exposed to freezing temperatures?

Presidents Grant, Nixon, and Carter stayed here, along with President George H. W. Bush, several governors, and various celebrities [source: Thayers Inn]. However, the buzz surrounding their visits to the historic Thayers Inn in Littleton, N.H., likely didn't compare to a more recent event that brought the inn into the spotlight.

On a cold Friday in January 2014, a waterfall cascaded from the top of the inn's grand staircase, flooding hallways throughout the 1843 building and turning the first floor parlors and restaurant into lakes.

A streak of freezing temperatures had caused a water pipe to burst in the attic, sending an estimated 500 gallons (1,900 liters) rushing out every minute until the leak was finally stopped. It took 10 to 15 minutes to shut off the water, resulting in enough flooding to fill a residential swimming pool. Ceilings collapsed, wood floors buckled, and antique furniture was warped [source: Sullivan].

Burst pipe incidents like these are made worse by lingering (and potentially costly) issues such as significant structural damage and the growth of mold. Even a small crack in a water pipe can release up to 250 gallons (950 liters) of water daily.

So how can you tell if your pipes are frozen and setting the stage for a potential disaster? The answer is simpler than you might think: If turning on the faucet yields no water, or if flushing the toilet doesn't refill the bowl, your pipes are likely frozen. Similarly, if you turn on a faucet to full flow and only a small stream of water trickles out, ice may be blocking the pipes. If you suspect freezing, it's time to call a plumber and shut off the water supply at the main line entrance [source: House Logic].

Naturally, this advice is most relevant in areas where temperatures have dropped to or below freezing (32°F or 0°C). As a general guideline, temperatures under 20°F (minus 7°C) put water in pipes at risk of freezing. However, wind chill can cause water to freeze even when temperatures are above 20°F [source: The Weather Channel].

Bursting at the Seams

As water's hydrogen and oxygen molecules transfer heat to the surrounding freezing air, they draw closer together. If the arrangement of these molecules stayed the same, all this compression would result in solid frozen matter that occupies less space than its liquid form. But water is different. Instead, the molecular arrangement changes during freezing, causing the substance to expand and take up more space as it turns to ice [source: The Physics Van].

When it comes to the water pipes in your home, this expansion of water as it freezes creates significant stress on rigid metal and plastic pipes, as well as pipe joints. Inventors take note: If pipes were made from a flexible material, the expansion of freezing water wouldn't cause damage and would save thousands of homes from disaster each year.

So, does water expanding into ice directly cause pipes to burst? Not exactly. The real issue arises when a pipe becomes blocked by ice in multiple spots. These blockages—found between the water source and a closed faucet—lead to a buildup of water pressure. Water can retreat from the ice blockage without pressure increasing on the upstream side, but downstream, the trapped water has nowhere to go, and the pipe eventually bursts. Joints are especially vulnerable to leaks, but cracks can appear anywhere along the pipe [sources: The Weather Channel, The Physics Van].

That's one reason it's wise to leave a faucet slightly open if you're concerned your pipes might freeze. Some believe that the constant drip prevents water from freezing, but in reality, water can freeze even while flowing. The true benefit of leaving the faucet open is to alleviate pressure buildup [source: The Weather Channel].

Though pipes may burst or leak as they thaw, which leads some to assume the melting process is the problem, that's not quite the case. The damage actually occurs days earlier when the pipes froze; you won’t see the full extent of the damage until the thaw because the ice blockage was temporarily preventing any leaks.

Prevent a 'Pipe'tastrophe

In colder parts of the U.S., homes are typically built with measures to shield water pipes from the harsh elements. Insulated pipes are usually placed in warm, interior sections of the house, avoiding unheated spaces like attics, crawl spaces, and exterior walls. In warmer regions, however, freezing temperatures are rare, and as a result, there’s less focus on properly insulating or placing pipes during construction. When a cold snap hits, this lack of preparation can lead to frozen pipes—and eventually, a watery disaster [source: The Weather Channel].

How can you prevent your water pipes from freezing, no matter where you live?

If you're in the midst of a cold snap, there are some additional precautions you can take to minimize the risk of frozen pipes.