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Roofing Siding Insulation RSI "Infrared Scanning and Computers Take Care of Roofs Before They Leak"

Infrared roof moisture scanning finds trapped wet insulation before leaks show. What the camera reads, the conditions it needs, and why cores confirm it.

Article by Dick Phillips

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Background on this topic from Inspec

A roof is usually wet long before it drips

By the time water shows up on a ceiling tile, the insulation above it has often been holding moisture for a long time. Water enters at a failed seam, flashing or penetration, spreads sideways through the insulation layer, and only reaches the interior where it finds a path through the deck. The stain on the ceiling and the breach in the membrane are frequently nowhere near each other.

That lag is the reason a moisture survey is worth doing on a roof that has not yet leaked. Wet insulation loses thermal value, adds dead load, corrodes steel deck and fasteners, and steadily undermines the membrane above it. Finding it while it is still confined to a few areas is the difference between a targeted repair and a tear-off.

What the camera is actually reading

An infrared camera does not see water. It reads surface temperature. Wet insulation stores more heat than dry insulation and releases it more slowly, so after a day of solar gain the saturated areas stay warmer at the roof surface into the evening while the dry field cools. The scan captures that difference as a thermal pattern, and the pattern is interpreted against what is known about the roof assembly.

Interpretation is the part that matters. Warm anomalies also come from mechanical equipment, hot piping below the deck, ponded water on the surface, standing debris, patches of different insulation thickness and areas of dissimilar surfacing. A thermal image on its own is not a moisture map; it is a set of anomalies that someone has to explain.

Conditions and access

A valid scan depends on the roof having taken in enough solar energy during the day and on a clear, dry, low-wind evening so the stored heat is released rather than stripped away. Surface water, snow, heavy dew and recent rain all suppress the pattern. Wind flattens the differential quickly. Roofs with a highly reflective surface, a ballast layer or an overburden such as pavers or a vegetated assembly may not produce a readable image at all, and a different survey method should be considered.

Scanning is done by walking the roof so anomalies can be marked in place while they are visible, with photographs and thermal images tied to a roof plan. Nothing about the survey interrupts the tenants below.

Verification by core sample

Anomalies are confirmed by taking test cuts through the assembly at representative locations. A core shows the actual condition of the insulation, the number and type of layers, the deck material, and whether the moisture is confined to the top layer or has reached the deck. Cores also establish what the roof is made of, which the thermal image cannot tell you.

The cuts are patched, and the confirmed conditions are used to calibrate the reading of the rest of the anomalies. A scan without verification produces a picture; a scan with verification produces a defensible quantity of wet area.

Turning the survey into a decision

The deliverable that owners use is a roof plan with the wet areas outlined and measured, keyed to the core locations and to the photographs. From there the questions become answerable: is the wet area small and localized enough to cut out and replace, is the leak source repairable, or has enough of the field been compromised that replacement is the sounder investment?

Recording the survey rather than filing it away is what makes the second scan valuable. Comparing today's wet-area map against an earlier one shows whether a condition is stable or spreading, which is a far better basis for capital planning than an annual visual walk alone. That record is the backbone of a building envelope management system and of the longer-term facility asset management programs owners build around their roof inventory.

Where scanning fits, and where it does not

A moisture survey answers one question well: where is the insulation wet. It does not tell you why. Determining the entry point still takes a physical commercial roof inspection of seams, flashings, terminations, curbs and drains, and sometimes a forensic roof investigation when the failure has already caused damage or is in dispute. The two work together: the scan tells you where to look hardest, and the inspection tells you what to fix.

Inspec inspects, tests and reports. We do not perform the repair or replacement work we recommend, so the extent of wet insulation reported is the extent we found. If you want a scan considered for a specific roof, contact us and we will tell you whether the assembly and the season make it worthwhile.

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Common questions

How does an infrared scan find moisture if the camera cannot see water?

The camera reads surface temperature, not water. Wet insulation stores more heat during the day than dry insulation and releases it more slowly after sunset. During that cool-down window, saturated areas read warmer than the surrounding roof and show as anomalies. Those anomalies are then verified by core sampling before anyone calls them wet.

What weather conditions are needed for a valid roof scan?

The roof needs enough solar loading during the day to build a temperature differential, a dry surface free of standing water, snow, ice and heavy dew, and low wind so the thermal signature is not stripped away. Scanning usually happens after sunset while the differential remains readable. Poor conditions mean the survey should be rescheduled, not forced.

Are test cuts really necessary if the scan already shows the wet areas?

Yes. Thermal anomalies can also be caused by conduit, mechanical equipment, interior heat sources, patches or varying insulation thickness. Cores at representative anomalies, plus a control core in an area that scanned dry, confirm whether moisture is present, identify which layer is wet and document the actual assembly. Cores are patched the same day.

Which roofs are poor candidates for infrared scanning?

Ballasted roofs, paver and protected-membrane assemblies, and some reflective or wet-applied surfacings mask the thermal signal, as do assemblies whose insulation does not retain water in a way that produces contrast. In those cases other nondestructive methods or direct investigation give better answers, and a survey should not be sold where it cannot perform.

How is an infrared scan different from a nuclear or capacitance moisture survey?

Infrared reads surface temperature patterns across the whole roof quickly. Nuclear meters measure hydrogen content on a grid, and capacitance meters read electrical properties near the surface. Grid methods sample points rather than the full field but are not defeated by wind, dew or a reflective surface. The assembly and the conditions decide which method suits a given roof.

Will wet roof insulation dry out on its own?

Generally no. Once water is trapped between a membrane above and a deck below, there is no meaningful path for it to escape, and it migrates laterally instead. It continues to degrade the insulation's thermal value and to hold moisture against the deck and fasteners. Wet insulation identified in a survey should be treated as a permanent condition until removed.

Can the survey be flown with a drone or aircraft instead of walked?

Aerial thermography can cover large roof areas or multiple buildings quickly and is useful for screening. It still needs the same weather window, and anomalies still have to be walked, marked and cored to be confirmed. Aerial imagery narrows where to look; it does not replace the on-roof verification that makes the results usable for budgeting.

What do we receive at the end of a moisture survey?

A written report with a roof plan showing the outlined wet areas, the core locations and what each core revealed about the insulation and deck, supported by thermal and visual photographs. The report describes the conditions during the scan and the limits of the survey, so the findings can be handed to a designer or used in capital planning.