This article is the second in a two-part series looking at the causes of frozen residential pipes and ways to prevent the problem. Part one discussed the science of frozen pipes. Here, BUILDER contributor Leonard Morse-Fortier provides three case studies of frozen pipe situations and what went wrong.

In the International Building Code, responsibility to protect pipes from freezing falls to the plumber who installed them. However, depending upon the sequence of construction, plumbers may have no way of knowing what future conditions might adversely affect the vulnerability of their work.

Even with care taken, things still go wrong. Consider the following three cases, adapted versions of real failures, where conduction and convection likely served as the principal reason a pipe froze.

Example 1. A new house has been built with the intention of keeping plumbing out of the way. A copper water pipe runs around the top of the concrete foundation wall, just inside the timber sill, and supplies water to two outdoor faucets (see Figure 1 in slide show at left). The contractor insulated the first floor for acoustics and warmth. When finishing the basement, a contractor installed wood-stud walls to the inside of the basement perimeter, insulated the walls, and finished all walls on the inside. As a result, the water pipe was now outside the building’s thermal envelope, lying on top of the concrete wall (see Figure 2 in slide show at left). With no heat from the basement reaching the foundation, the concrete wall eventually cooled with the outdoor temperature. Because the pipe was in direct contact with the concrete, the pipe cooled rapidly as well. The pipe froze and burst at an elbow, resulting in water flooding the basement.  

SOLUTION: The pipe freeze resulted from excluding the water pipe from the thermal envelope. However, the pipe failure could be prevented, or at least minimized, with an interior shut-off and drainage system. If the pipes included an interior shut-off somewhere well within the thermal envelope, the air in the pipe would at least relieve pressure if water froze. Though, with a shut-off system, the two outdoor faucets should be drained for the full length of the exposed pipe.

Example 2. A contractor was building a new house with a master bedroom suite on the first floor and noticed the large attic space above the master suite. He decided he could improve the house's marketability by adding a bathroom there. Both the supply and drain pipes for the second-floor bath were included in the master bedroom ceiling—and the ceiling was insulated for acoustic as well as thermal reasons. The shower was plumbed to supply water through the interior wall, drains were vented through this wall, and the vent pipe exited the house above this interior wall (see Figure 3 in slide show). The interior wall was not insulated, so warm air within that wall could flow up through the attic and out through roof vents above. Cold air entered through the soffit vents that surround the master bedroom ceiling and was likely expected to flow up and over the second-floor bathroom. Unfortunately, this air was also pulled across the underside of the bathroom floor. The flow of cold air was strong enough to freeze the pipe supplying the shower, eventually causing that pipe to rupture. 

SOLUTION: This failure resulted from a poor understanding of how air could flow through the new construction. The master bedroom ceiling was properly insulated, the soffit vents were intended to allow air to flow into the attic, cool the underside of the roof, and flow out at the roof top.  Unfortunately, the details of construction allowed air to flow across the top of the ceiling insulation and up through the interior wall where it cooled the plumbing. Future problems were prevented by closing off the unintended air passage .

Example 3. A new condominium building included substantial balconies that cantilevered from the building structure. The building itself was wood-frame, but included wide-flange steel beams that cantilevered from inside to support the exterior balconies. The kitchen overlooked a portion of the balcony, and the water-supply pipes for the sink passed alongside the steel beam before turning upward to extend through the floor, into the cabinet, and to the sink. The pipe was above the first-floor insulation, which was installed to ensure the pipe was located on the warm side of the insulation (see Figure 4 in slide show—only one pipe is shown). However, the steel beam acted as a thermal bridge, as it extended from the warm side to the cool side of the insulated envelope. 

On a very cold night, the steel beam cooled to well below freezing and the pipe running alongside it froze and burst.  

SOLUTION: Here, the pipe froze because of two possible reasons: one, it was too close to the steel beam; and two, the steel beam extended through the insulation, providing a possible path through which heat could escape. The freezing steel beam, along with the cold air adjacent to the beam, drew enough heat from the pipe that the water eventually froze and burst the pipe. If the pipe itself had been insulated, that likely would have prevented heat loss through convection, and would have slowed the rate of conductive heat loss as well.   

There are likely countless other examples of unfortunate construction details that did not appear obvious at first, but which led to freezing and subsequent damage. A colleague of mine has a sign on his office that reads, “Think Thermally.”  While this may be easier said than done, the principles are straightforward enough. Pipes with water will freeze where winter temperatures can cool them. We can keep them warm by making sure they are always in warm places, we can be vigilant that we don’t inadvertently cut off their access to warm air, and we can stop and think about what might go wrong and try to prevent it.