FIGURE 1: Thermal imagers can provide a view of the roof surface and show insulation and moisture issues during inspection from a drone. This particular image is a blend of a color image (taken during daylight) and a thermal image shot after dark. Before sunset, we walked the roof with a handheld scanner and used spray paint to outline the areas with temperature anomalies. The light gray areas inside the orange marking on the roof illustrate how closely the drone thermal image compares with the results of walking the roof.
Inspecting large commercial flat roofs can be time consuming, expensive, and dangerous. Using drones to perform inspections of these roofs can make inspections faster, safer, and less expensive. In fact, the benefits of drone inspections have become so obvious that widespread adoption of this technology has radically increased during the last five years.
Thermal Roof Inspections: Why Not Just Walk The Roof?
Thermal (infrared) imaging uses specialized cameras to make still images and videos of the differing amounts of thermal energy being reflected from a surface. While this generally corresponds to the relative temperature of an object, meaning that things that appear to be giving off more thermal energy are hotter than the things around it, that’s not always the case. Different materials and surface finishes impact an object’s ability to show its heat energy. This natural phenomenon can cause a surface to be more reflective, causing it to look much hotter or colder than it really is. Understanding this concept and others point out how vital hiring a person who is not only a licensed drone pilot but also a Thermographer..
FIGURE 2: Thermal cameras can provide temperatures of a surface and show insulation and moisture issues during roof inspection from a drone.This particular image shows a 20+ year old roof in desperate need of attention. It also illustrates that thermnal drone roof inspections are not very concerned with actual temperatures, but rather with the “big picture” of which areas show anomalies that need to have destructive testing performed.
A Drone is An Efficient Piece of Equipment for Roof Inspection
Using handheld thermal cameras to inspect membrane covered roofs for potential moisture damage is nothing new and often the same standards and practices apply when using a drone. That said, there are potential dangers in interpreting data from a handheld device.
ASTM standard C1153 lays out the guidelines for cameras, environmental conditions, and moisture verification when doing thermal inspections of membrane roofs, and it applies to drone inspections as well as manual inspections. Basically, the requirements are as follows:
· Inspect after sundown. Thermal loading caused by direct sunlight on a roof can affect accuracy.
· Have at least a 10 degrees Celsius (50 degrees Fahrenheit) temperature difference between the underside of the deck and the roof surface. The greater the contrast, the easier it will be for operators to detect potential issues.
· Make sure there is no standing water, snow, or ice, and no debris on the roof. Those conditions on the surface can mask potential problems below the surface of the roof membrane.
· For best results, inspect when the roof has been exposed to moisture within a week, but not within 24 hours of the inspection.
· The ASTM Standard also addresses the danger of walking roofs at night, recommending at least 2 people for the operation. The standard does not address additional safety issues relating to rooftop access such as ladders and man-lifts.
During the day, the roof surface is exposed to sunlight and absorbs the energy of that solar radiation. After the sun goes down, the areas of the roof with dry insulation will cool off more rapidly than the wet areas. Because of the ability of water to hold heat, it will take longer to change temperature and will therefore present a different thermal signature than the dry areas.
It is important to note, however, that while these thermal anomalies may be indicative of possible moisture intrusion, they are not diagnostic. A roofing contractor will still need to get on the roof to verify through destructive testing whether there is moisture under the membrane. The advantage drones provide is to cover large roofs in a matter of minutes, capturing a series of overlapping images that are then stitched together into a large thermal orthomosaic of the entire roof. Inspection reports using hand held imagers cannot do this. Part of the report provided to the customer should be outlining the anomaly areas so the contractor will know exactly where to go to perform the testing.
Savings
We recently inspected a 675,000 square foot roof. Considering that a high-performing crew can walk about 10,000 to 20,000 square feet per hour at the best, the inspection of that roof would have taken from 35 to 65 hours to inspect. Since the roof areas will reach equilibrium in about 6 hours, that would require 6 to 11 nights to perform that same inspection that we performed in less than 2 hours. In addition, we were able to present the client with an orthomosaic showing the entire roof in one image.
Cautions
Buildings with overpressure interiors such as hospitals and medical laboratories can cause patterns that look like an image of the insulation panels. This illustrates why the thermographer must know the roof structure including membrane, insulation, fastening and decking. Each of those details can and will make a difference in how the anomalies are presented.
Drones give professionals the ability to inspect large areas of roofs quickly and safely without having to spend hours on potentially dangerous roofs to do their inspections. Sidebar note: 80% of all falls off of roofs are fatal. The latest advances in thermal imaging brings even more advantages to these drone inspections – from rapid moisture inspections to detailed examinations of roof mounted mechanical systems.
KEYWORDS: commercial roofing drones in roofing flat roofs FLIR Systems imaging inspections roofing technology
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