Current Roof Trends Point To Cellular Foams and White Membranes
For more than a decade, the use of single-ply roofs has been on the rise. These roofs feature white reflective membranes and use cellular foam for insulation. The main reason for this trend is cost, as these roof systems are cheaper to install than a conventional roof, especially with government incentives to build roofs that are more reflective and better insulated.
Cellular foams made of high density material won’t absorb water until the UV compromises the foam (about 5-7 years). Any water entering the roof via a membrane breach will go directly into the building, which is definitely the worst case scenario.
Because the water goes directly past the non-absorbent insulation and into the structure, there is no reason to check for entrained moisture. This is also true for assessments on storm damaged roofs that are new, but explaining this to a contractor looking to check off a box on a form can be difficult, if not impossible.
If roofs with non-absorbent foam insulation had a thin layer of absorbent insulation installed just below the membrane, this problem would be rectified. The small added initial cost would be more than offset by the ability of a professional thermographer to pinpoint the location where water has breached the roof. In essence, the absorbent insulation is merely a sacrificial layer to the roof, not unlike the roof is to the building below.
Which Infrared Imaging System is The Best?
When selecting which imaging system to use, certain factors must be considered, such as:
- Software Compatibility
- Technical Support
- Speed of Image Data Acquisition
There are three specifications that should be considered, which will ultimately determine the success of a job, especially when infrared is used.
Thermal Sensitivity describes whether the detector is capable of reading temperature differences minute enough to complete the job. The camera’s sensitivity may be thoroughly tested during the night as the roof changes thermally, to the point where the subtle differences between dry and wet areas is no longer apparent. As a point of reference, the minimum specs for roofs should be as low as 50mk for thermal sensitivity.
Spatial Resolution refers to the detector’s ability to render a picture that clearly defines the area you need to resolve. A more powerful lens can make up for a smaller pixel array, but the area of coverage will then be limited. Additionally, every lens has some signal degradation, and the further you get from a subject of infrared imaging, the more useful the data becomes. It is still possible to adjust the distance to a roof target, and this spatial resolution can be very important, especially when aerial imaging is utilized. However, it can also be limiting.
While spatial resolution minimums ultimately depend on the distance to the target, 320×240 pixels is the minimum resolution required for under-roof and on-roof imaging. When using the elevated method, this resolution may be sufficient, but 640×480 pixels is recommended. For aerial imaging, 1024×1024 pixels is required.
Detector Wavelength isn’t an issue for roof thermography. However, midwave arrays are better than longwave arrays because they handle reflections better. This is especially true when conditions are cold. It is important to have good sensitivity and spatial resolution if you’re using a microbolometer.
Longwave microbolometers are very popular and highly used imagers because they are less expensive and require less maintenance than midwave imagers, and they will almost always do the job required of them.
When scanning roofs, all three of these specifications should be accounted for, especially when conditions are poor. If you’re a roof thermographer you should never pinch pennies when selecting an infrared imager for roof thermography, as the applications are some of the most demanding in the field of thermography.