Detecting Leaks with Infrared Thermography
By Stephen A. Varone, AIA and Peter Varsalona, PE, CEM, CBCP
Our recently converted condominium in Brooklyn has been experiencing major leakage issues in the top-floor apartments, along one apartment line, in a stairwell, and in the lobby. Contractors have made as-needed repairs to the roof over the past year, but eventually the leaks returned. Before we undertake a full-scale roof replacement, the boards wants to have a thorough leakage investigation conducted to determine the cause of the water penetration, which we fear may be more than just a defective roof. We’ve heard about a service in which an infrared camera is used to take photos of the roof and other areas of the building to locate leaks. How exactly does it work, and how effective is it?
Infrared thermography is a diagnostic tool used to detect potential building problems, including water penetration, heat or cooling loss, blockages in plumbing systems, malfunctioning mechanical systems, overloaded electrical circuits, structural defects, and sub-standard building construction. The main advantage of an infrared survey is that it gives a view of building conditions beyond what can be seen in a visual-only survey.
Another advantage of infrared thermography is that it is a non-destructive method of testing, so it does not disturb the area being investigated. When used on mechanical and electrical systems, it doesn’t interfere with the operation of equipment, so there’s no need to interrupt operations or plan for shutdowns. For leakage investigations, probes may still be needed to get a better look at underlying conditions of a roof or a facade, but an infrared survey can help pinpoint where the probes should be taken, minimizing the added cost and time.
How Does It Work?
The science behind infrared thermography is basic: Vibrating molecules generate electromagnetic energy. At higher temperatures, molecules move faster and emit more energy, This energy—infrared radiation—isn’t visible to the human eye, but it can be detected with a camera equipped with an infrared sensor.
Thermal differences appear as different colors in infrared light. By analyzing the color distribution in thermal images, it is possible to locate the areas of a building that are abnormally warm or cool, which may indicate potential defects such as water infiltration, missing insulation, drafty windows and doors, or an inefficient boiler.
Using Infrared to Detect Leaks
Once water has entered a building it can travel far and wide, making it difficult to find the sources of the leak and assess the extent of damage. Infrared thermography is particularly useful for detecting water in hard-to-see areas, such as underneath roofing membranes, behind walls, and inside shafts and conduits. Thermal surveys are also effective for detecting moisture that has worked its way deep below the surface of the roof and saturated the roofing insulation.
Because an infrared survey highlights the thermal differences in building components, it must be conducted under the right conditions. The ideal situation for a roof survey is a clear day, after the sun has heated up the roofing system and any trapped underlying water. As the sun goes down or as the roof is shaded by nearby buildings or structures, the roof cools (what is called radiational cooling), as does moisture under the membrane. But because water has a high thermal capacity—i.e., it retains heat longer than solids—the trapped water cools much more slowly than the roofing surface. Therefore in infrared photos taken of a roof that has been heated by the sun all day and then cooled off, thermal differences can be seen between the cooler areas of the roofing surface and the warmer ones where water is underneath the membrane.
An infrared survey highlights the thermal differences in building components.
The thermographer begins the roof survey by first conducting a visual observation, looking for obvious defects that could cause leaks, such as a torn or blistering roofing membrane, missing or defective flashing, cracked or spalling bricks in parapet walls, open coping joints, ponding, etc. The thermographer also notes the orientation of the roof to the sun, the position of surrounding buildings or structures that cast shadows on the roof, and any debris or other items that could skew the results of the infrared scan.
Depending on the air temperature, the type of roof construction, and the length of time the roof was exposed to the sun of that day, the thermographer waits anywhere from 15 minutes to an hour after the sun leaves the roof to performs a scan with the infrared camera. Analyzing the color distribution in the scan, the thermographer can see which areas along the roof are warmer (typically red in the infrared spectrum of colors). Warmer areas, which indicate the possible presence of water underneath the surface, are marked off with spray paint and photographed to capture the thermal differences, which can be as little as 2 degrees Fahrenheit to 20 degrees or more. The infrared camera also takes regular color photos of the same locations to compare side by side with the infrared images.
Evaporative Cooling
For roofs not directly exposed to the sun, the roof and any water trapped underneath the membrane do not heat up enough to show the thermal differences when cooling. In such cases, instead of relying on radiational cooling to reveal water infiltration, the scientific principle of evaporative cooling is applied. Without direct sunlight, the temperature of the roofing surface is close to the ambient temperature. The water beneath the roof surface, however, which has not been heated from the sun, cools as it evaporates. Therefore, in the thermal images the areas on the roof with water penetration display as cooler than dry areas, as opposed to warmer because of solar radiation.
Based on the areas of moisture beneath the roofing membrane as indicated in the infrared images, as well as the visually observed conditions, the thermographer can target the exact locations where investigative probes should be taken to confirm the presence of water, determine the extent of deterioration, and assess any structural damage to the underlying roof deck.
Exterior Walls
In addition to the roof, facades are a critical component in keeping water out of a building. Defects in exterior walls, such as cracked or spalling brick, loose masonry, and deteriorated pointing, allow water to penetrate the building, resulting in leaks and deterioration. In addition, a building that is not watertight also lets conditioned air escape, increasing a building’s energy costs.
A thermal survey of the building envelope can identify water that has entered behind walls, as well as missing insulation and otherwise faulty construction that allow water and air infiltration. As with an infrared roof survey, either the radiational cooling or evaporative cooling method can be used, depending on whether the facade is directly exposed to the sun.
Interiors
As part of the leakage evaluation, the thermographer also evaluates the areas inside the building where water damage is evident. Stains, discoloration, peeling or cracking paint, mold, etc. are telltale signs of water infiltration. But although the outward signs of a leak may show on a wall or ceiling, the source of the leak and the path it has taken are usually harder to track.
Using an infrared camera, the thermographer takes a series of photos of the leakage area. Using the evaporative cooling method (because inside walls are not typically exposed to the sun), the cooler areas in the infrared images indicate likely water penetration. Because water can travel extensively, the cooler areas may be hidden behind walls or in locations far away from the visible damage. Using the thermal images as a guide, the leaks can be pinpointed with much greater accuracy and followed back to the entry points along the exterior building envelope.
Thermographic Quality
The effectiveness of infrared thermography as a diagnostic tool depends heavily on proper use of the infrared camera and conducting the survey under the right conditions. An infrared roof survey conducted in the middle of a hot, sunny summer day, for example, typically produces images without appreciable thermal differences because all of the elements—roofing surface, water, brick walls—show the same high temperature. Only when the roof cools after hours of sun exposure will meaningful thermal differences be evident in an infrared image.
Similarly, an infrared survey taken on a cloudy day produces inconclusive thermal patterns in the infrared images. The cloud cover prevents the roof from heating up during the day, which reduces radiational cooling at night, minimizing significant temperature differences. Roofing surfaces must also be dry during an infrared survey because in thermal images the moisture underneath the membrane is indistinguishable from wet areas on top.
Infrared thermography
is most effective when used in conjunction with a visual evaluation.
While infrared thermography is an invaluable tool for investigating leaks and diagnosing other building problems, it is most effective when used in conjunction with a visual evaluation. Colors that indicate the presence of water in the infrared images must be confirmed by hands-on examination and possibly by using a moisture meter and/or opening investigative probes. Some spots that appear as warmer or cooler (depending where in the building the images were taken) may not be water; they could be cooler areas caused by drafts or missing insulation, for example. But even in those cases, the infrared survey helps pinpoint heat and energy losses that should be addressed.
Certified Inspectors
For best results, the person conducting an infrared survey should be a Certified Infrared Thermographer with professional training from a recognized infrared thermography organization that meets the standards of the American Society of Nondestructive Testing (ASNT). Certification also requires classroom and web-based education and hands-on field experience.
Properly evaluating a building’s conditions, however, requires more than just taking infrared photos, even by a certified thermographer. The images must be properly interpreted with an understanding of what conditions cause water penetration and heating/cooling loss in a building, and how they can be effectively addressed with a comprehensive repair program. The thermographer must have a thorough knowledge of building systems based upon training as an engineer, architect, or other building professional. Expect to pay anywhere from $3,000 to $6,000 for an infrared study, depending on the project scope.
Used properly by trained professionals, infrared thermography can certainly help you see your building in a new light.
Stephen Varone, AIA is president and Peter Varsalona, PE is principal of RAND Engineering & Architecture, DPC. This column was originally published in the September 2012 issue of Habitat Magazine.