Frozen Pipes Dilemmas: The Hard Cold Facts of Insulation Effectiveness and Building Tightness

When the air temperature inside the heated space is cold enough to freeze plumbing, clearly there's a problem.

January 01, 2001

Every winter, just after the first cold snap, I always get a wave of calls from panicking homeowners with frozen pipes. Surprisingly, many of these frustrated homeowners do not live in drafty antique buildings, but in newly constructed homes. How can a fully insulated home with double pane windows and tight doors have frozen pipes-especially when those pipes are located in the middle of the heated space?

Just the Tip of the Iceberg

When the air temperature inside the heated space is cold enough to freeze plumbing, clearly there's a problem. Inspections of these homes confirm that, while frozen pipes may be the most obvious symptom, they are just the tip of the iceberg. Most pipes freeze up as a result of cold air getting inside the building. Once this cold air penetrates a building cavity it will disperse in a widespread fashion, moving without restriction inside the heated space. Many homes actually have similar problems with freezing air entering the structure, but for a variety of reasons the cold air has not yet reached the plumbing. While a frozen or burst pipe presents an immediate problem, the real issues are the efficiency and comfort problems created by poorly installed or inadequate insulation and building shell details that don't work.

As specialists in diagnosing and treating comfort and efficiency problems in buildings, our company has seen more than its share of cold homes and frozen pipes. We know that these problems are much more common than expected. But how is all this cold air sneaking into a home? While homeowners are often aware of cold drafts entering through windows, what may not be as obvious are the much larger amounts of heated air that are rising and exiting through the ceiling. Homeowners and even many builders do not know that an insulated ceiling may be full of holes and heat loss areas. Today's amenity-packed homes often contain hidden pathways interconnecting cables, wiring, mechanical runs, and duct work. These pathways can covertly lead to unheated spaces, attics, or even to the outside. In cold, windy conditions these open paths allow cold air to migrate unobstructed inside the heated space.

Using specialized diagnostic tools, such as an infrared imager and a blower door fan, we can reveal the otherwise invisible dynamics of a home's air leakage and heat loss problems. An infrared inspection measures surface temperatures, helping to make heat loss areas visible. Testing with a blower door fan can assist in measuring the draftiness of a building. In diagnosing frozen pipe and cold house complaints, these tools can pinpoint the exact locations where cold air is entering a home from outside and heated air is escaping.

Testing homes using this type of diagnostics is changing some of the ideas we have about building efficiency and comfort in some surprising ways. Consider the following:

  • Interior partitions and ceilings located inside the heated space can be just as cold as an outside wall.
  • The real culprit for drafts and comfort problems are not the windows but the ceilings and concealed framing details.
  • In some homes these concealed air leakage areas can add up to twenty square feet. That size of a leakage area is like leaving a door wide open all winter long!
  • Adding insulation to a home does not necessarily result in a tighter home.
  • Insulation in many homes is performing well below the promised effectiveness or R-value label because of air movement inside walls and ceilings.
  • By understanding and controlling air movement, we can improve the comfort and efficiency of many, if not most, residential buildings and improve the occupants' health.

Start by Identifying the Leaks

Occupants are often not aware of the heated air leaving at the top of the house. These "attic" air leakage locations, which are referred to as exfiltration, can be just as responsible for comfort and efficiency problems as the air being sucked in the windows on the lower level. In fact, sealing a hole that allows air to escape at the ceiling level will result in less drafts infiltrating from below. Therefore we always advise homeowners to start at the top level when looking for opportunities to tighten and insulate the building shell. Gaps around ceiling fixtures and registers should be caulked. Pull down attic stairs, attic hatches, and kneewall doors should be insulated and weather-stripped. Large air leaks in the ceiling are often hidden by attic insulation. Air movement will often result in black streaks on the insulation, making them easy to locate and seal with caulking or foam sealants.

On cold windy nights check recessed can lights in the ceiling for signs of cold air. Likewise cold air coming out of electric outlets and switches on interior walls is a sure sign of widespread infiltration. One enterprising homeowner we encountered placed the sensor of her indoor/outdoor thermometer into a problem ceiling cavity between two heated floors. The temperature in the "heated" cavity was twenty degrees colder than the air temperature in the kitchen below. Further investigation revealed that the open web type ceiling trusses were exposed to the adjacent unheated garage.

(All too) Common Frozen Pipe Scenarios

One of the easiest frozen pipe situations to diagnose and repair involves the open plumbing chase. During construction, framers often provide an extra deep wall cavity adjacent to the shower unit. This detail, sometimes referred to in the industry as the "wet wall," could be more appropriately named the "ice wall." This wall contains the shower pipes and valves, while conveniently hiding the large penetration through the ceiling and roof line needed to accommodate the vent stack. Since this topless partition is open to the unheated attic or roof cavity, cold air can move down into the partition containing the plumbing. The rest is just a matter of temperature and time. (Click here for an illustration)

What may appear to be an obvious solution to this problem leads to another misconception that is all too common in the construction industry today. Why not just add some insulation to this critical area? Unfortunately many of the common insulating materials used today do a poor job of stopping air movement. Loose blown fiberglass and batt insulation can effectively slow conductive heat loss, but are susceptible to air moving around and through them. In fact most of the frozen pipe chases we encounter are already "covered" with insulation.

Compounding the problem, laboratory testing has revealed that air moving through fiberglass can degrade the insulation's performance to well below its rated R-value. Building scientists and researchers have concluded that adding insulation is not enough. Insulation only works when it is installed in an air tight configuration.

Another common problem is outside air infiltrating ceiling cavities between heated floors via the eave. This is most evident in homes with one story and a half. (Click here for and illustration) As is shown here, this kneewall floor and wall are insulated. However outside air can easily bypass at the critical juncture and penetrate the heated cavity beyond.

One frustrated homeowner had just moved into her newly built home when the bathroom plumbing, which was located next to a kneewall, froze. Unfortunately the homeowner called us only after hiring a number of different insulation contractors to address the problem. By the time these various contractors had attempted to fix the problem, they had managed to completely fill the whole kneewall cavity with a variety of different types of insulation. (Click here for a photograph) Despite the four foot high "superinsulation" attempt, infrared scans taken directly below clearly showed that cold outside air was still penetrating the heated space. What was missing was an airtight barrier that would isolate the cold outside eave space from the heated cavity that contains the plumbing.

Another common problem starts with placing a tub or shower unit adjacent to an unheated attic or kneewall. During the construction process the tub or shower unit is fastened to the bare studs prior to installing the wall board. While some contractors are now more careful about installing insulation behind the tub or shower, it is still not air tight. Even if the cold air from the adjacent space does not freeze the pipes, you can bet the unsuspecting occupant is in for a real cold shower. (Click here for a photograph)

What's the Fix?

The good news is that there are effective solutions for these problems. A well designed retrofit can prevent refreezing and improve a home's overall efficiency and comfort. The real cure involves sealing attic air leaks and stopping outside air infiltration. This strategy, which is often referred to as air sealing, is not meant to replace the insulation, but to supplement it by providing an air tight interface between heated and unheated spaces.

Defining the best location to install this new air tight interface can be tricky in some cases. Problem typically arise when the interior wall board or ceiling is not continuous. Details, such as ceiling height changes, kneewall floor transitions, and other framing offsets, can hide noncontinuous framing. These critical junctures may be covered with plaster board on the heated side but are still indirectly exposed to the outside air.

Depending on the existing conditions and access, there are a number of viable air tight materials available to address these situations. The goal is to construct an air tight barrier or envelope that effectively isolates the insulation from unheated space. This air barrier must be contiguous and aligned with the thermal barrier, as defined by the insulation. The critical point is to make both envelopes continuous.

Even the smallest gap or crack is susceptible to air movement. Penetrations for wires and plumbing should be sealed with caulk. Gaps around windows should be sealed with materials other than fiberglass. Joints, gaps, and seams between framing members and plaster board should be sealed or gasketed.

When selecting an air tight material to seal the inevitable gaps in wood framed homes, keep in mind that durability is an issue. Consider blocking and sealing large holes with rigid materials such as insulation board, plywood, or sheet rock. Make sure that these materials are carefully sealed into place with caulk or insulating foam. (Click here for a photograph) For less accessible areas, we have had success with more aggressive air sealing techniques such as super expanding foams (Click here for a photograph) and dense packed cellulose treatments. For large surface areas such as the cold back side of a shower it is important to have an air tight seal but make sure the retrofit does not trap water vapor. For this situation we use an air tight, yet moisture-permeable, housewrap (Click here for a photograph)

Call in the Expert

Many homes could benefit from air sealing repairs. Studies show that in an insulated home, air leakage can account for up to 40% of the heat loss. Unfortunately, many drafts in buildings are left untreated because of the elusive nature of air movement. Building performance contractors and house doctors with a background in building science, and using the right diagnostic equipment, can help you locate air leakage locations and thermal problems. Consider using one to help you prioritize a retrofit strategy that will eliminate air leakage and help the existing insulation to do its job. The only things you have to lose are annoying drafts, cold showers, high fuel bills, and frozen pipes.

Bruce Torrey is a Certified Infrared Thermographer and consultant with the Massachusetts based company, Building Diagnostics. As specialists in health, comfort and efficiency improvements they service both new construction and existing buildings. He can be reached at

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