What to Expect When a Thermographic Professional Arrives to Check for Leaks
Sept. 4, 2012 — A thermographer begins a 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 that day, the thermographer waits anywhere from 15 minutes to an hour after the sun leaves the roof to perform 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.
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
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In addition to the roof, façades 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 façade 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.
With 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.
Watch for our next article, on the effectiveness of thermographic quality.
Stephen Varone, AIA, and Peter Varsalona, PE, are principals at Rand Engineering & Architecture.
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