Our client faced a significant challenge: managing 5.2 hectares of flat bitumen felt roof. To put the scale into perspective, an average housing estate in Ireland spans between one and three hectares. This asset was huge, and any undetected issues like leakage and moisture could easily lead to major malfunctions and exorbitant costs.
The question they brought to Engineers With Drones was simple: could we provide a fast, low-cost solution using drone and thermal technology? They needed to find and eliminate water damage and moisture intrusion beneath the felt without walking the entire surface and relying on the naked eye - which simply cannot detect these hidden problems.
As Bob Foley, founder of Engineers With Drones, put it: "They were asking if drone technology coupled with thermal technology could be a solution to that problem."
A thermal drone survey of a 5.2-hectare flat bitumen commercial roof, combining drone technology, thermography, and orthophotography to map surface heat variations and identify hidden moisture intrusion beneath the felt.
The total flat roof area surveyed safely and efficiently. Comparable in size to two or three average Irish housing estates.
RGB orthophoto, daytime thermal orthophoto, and nighttime thermal orthophoto - captured across two sessions on the same day for total transparency.
In-house developed GCPs, compatible with both RGB and thermal sensors, deployed across the full roof area to ensure precise geospatial data.
A plain-English PDF report, a marked-up thermal orthophoto, an unmarked thermal orthophoto, and an RGB orthophoto - all instantly actionable in the field on an iPad.
A quick, reliable, and cost-effective solution using our latest thermal-imaging technology.
The expensive, time-consuming traditional approach.
To provide the client with clear-cut conclusions, Engineers With Drones used three advanced technologies: precision drone flight, thermography, and orthophotography.
Orthophotography is a highly precise surveying technique. An orthophoto is a precisely stitched collection of photographs where each image is orthorectified - meaning every pixel is viewed from directly overhead. The result is a single, geometrically accurate top-down image of the entire asset that can be measured and navigated without needing to step foot on the roof.
A thermal orthophoto applies this exact principle to thermal imagery. Instead of a standard visual map, we deliver a thermographic map of the entire surface, precisely stitched and georeferenced. By combining an RGB orthophoto with daytime and nighttime thermal orthophotos, our engineers delivered a complete, instantly actionable picture of the asset that no single technology could achieve alone.
Due to the colossal scale of the roof, we deployed custom ground control points across the entire area. Developed in-house, these GCPs are compatible with both RGB and thermal sensors, ensuring the highest level of photogrammetric accuracy across all datasets.
Once the nighttime dataset was processed, we created a precise thermographic map of the 5.2-hectare roof. In this thermal orthophoto, blue represents cold, red represents hot, and yellow sits in the middle.
We are more than just drone pilots; our primary qualifications are in engineering, and correctly interpreting a thermal orthophoto requires that technical expertise. A commercial roof of this size has numerous legitimate heat sources: vents discharging warm air, rain gutters, and downpipes. These all appear in the thermal imagery and must be accurately identified to prevent false defect reporting.
Vents naturally appear in large numbers across a roof like this. They present as discrete, defined heat sources and are easily identified by their shape and pattern. Rain gutters and downpipes present as repeating linear or point features along the edge; the heat radiating up from internal pipes makes them visible. These are expected, safe heat sources, not malfunctions.
Moisture intrusion presents entirely differently. The critical indicator is what we refer to as the inkblot pattern: an irregular, diffuse area of retained heat with no logical external heat source. While a vent has a strict, defined shape, water damage spreads organically, as thermal energy radiates outward from the hidden moisture.
As Bob puts it: "the inkblot pattern is one of the key elements that really demonstrate water ingress issues in any location."
Water damage also frequently tracks along linear features, such as seams and overlaps in the felt where a breach has occurred. Distinguishing this structural failure from a standard building feature like a lightning conductor is exactly where our engineering backgrounds add the most value.
Total transparency: if there is standing water on the roof at the time of the survey, the inspection cannot yield actionable results. Surface water generates its own thermal signature, completely masking the signature of the moisture trapped beneath the felt. In such cases, we prioritise reliable data over a quick finish; we will pause operations and return when the conditions are right.
We know what we're looking for, and we know how to find it - which means understanding that thermography behaves differently depending on the time of day. On a sunny afternoon, the solar heat absorbed by the roof overwhelms the thermal signature of any moisture intrusion underneath. The daytime dataset we captured confirmed this: it showed a building with no apparent defects because the sun's heat dominated the data. We captured this deliberately to demonstrate exactly what bad data looks like.
Actionable data is captured after dark. During the day, the matte black felt roof absorbs intense solar heat, and any water trapped beneath it does the same. After sunset, the dry areas of the roof cool rapidly. The wet areas, however, retain their heat longer because the trapped water stores more thermal energy. The optimal window for our engineers to detect this variation is roughly two to three hours after sunset on a cold day - after the dry roof has cooled, but before the wet areas have cold-soaked to the surrounding temperature.
Wait too long, and the hidden problems disappear again. A pre-dawn survey on this same roof would reveal nothing, as the water would have cold-soaked overnight to match the temperature of the dry areas.
Whenever anybody says that they can see through something with thermal, what they're actually saying is they can see the heat register of the properties of that object, not that they can see through it. So our drone cannot see through a roof, it can see the difference in heat degradation in the various structures of the roof, which is a very, very big difference.
See the thermal orthophoto data and our expert defect identification process in action. Watch exactly how three distinct datasets - RGB, daytime thermal, and nighttime thermal - combine to reveal hidden moisture intrusion and deliver a complete, instantly actionable picture of the roof.
We understand that you need answers fast. The client received a plain-English PDF report alongside three distinct deliverables: a thermal orthophoto with every issue clearly marked, an unmarked thermal orthophoto, and an RGB orthophoto showing each location in real colour. Using just an iPad, anyone in the client's team could zoom into the maps and walk straight to the precise location of the hidden moisture.
When managing 5.2 hectares of flat roof, the difference between blindly walking the surface hoping to spot an invisible problem, versus navigating directly to verified targets, is monumental. It transforms a needle-in-a-haystack guess into a rapid, targeted, and cost-effective remediation plan.
As Bob Foley put it: "The client was very happy with the work, said it was very useful and I believe they were able to then go about fixing a lot of the issues that we identified or more importantly verifying that they were issues and once verified then fixing them."
You can find out more about our roof inspections or our building inspections, or read our guide on how to inspect a roof with a drone. Alternatively, you can contact us here to ask what we can do for you.
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