Roof thermography uses an infrared camera to identify—without drilling any holes—areas where the insulation is wet and heat is escaping. When done properly, it turns a complete roof replacement into a targeted repair covering just a few square meters.
Key Takeaways
- The camera does not “see” water: it measures surface temperature variations caused by the thermal inertia of the damp insulation.
- The ASTM C1153 standard governs the detection of wet insulation in roofs and requires an inspection to be conducted at night, following a sunny day.
- A useful reading requires a dry roof , free of snow and strong winds; otherwise, the image is unreadable.
- In an attic, hot spots almost always indicate a problem with insulation or ventilation, not a leak.
- The Quebec Building Code currently requires approximately R-41 (RSI 7.22) for attic ceilings, whereas many homes built between the 1960s and 1990s have ceilings with a maximum insulation value of R-20 or R-28.
- Any thermal anomaly must be verified through a physical inspection before anything is demolished.
The measurement is taken after sunset, when the roof cools down faster than damp areas.
What the thermal camera actually sees on a roof
An infrared camera does not detect moisture, holes, or cracks. It detects the thermal radiation emitted by the surface and converts it into a temperature image. It is the contrasts in this image—known as thermal anomalies—that indicate a problem beneath the membrane or shingles.
Three types of defects are clearly visible under infrared light:
- Water-saturated insulation beneath a flat roof membrane, which retains daytime heat longer than dry insulation;
- Heat loss and thermal bridges around skylights, access hatches, drains, and changes in level;
- Attic insulation defects: insulation that is compacted, displaced by the wind, or missing above the gable walls.
What thermal imaging does not show, however, is the exact thickness of the insulation, the actual age of the membrane, or the precise source of the water. It pinpoints the location; it does not provide a diagnosis on its own.
The physical principle: the thermal inertia of water
Water stores much more energy than mineral wool, polyisocyanurate, or air trapped within dry insulation. On a flat roof, this difference results in a measurable disparity: after a sunny day, the sun heats the entire surface, and then the roof cools rapidly at sunset. Areas where the insulation is saturated remain warmer for longer and appear as very distinct light spots.
In winter, the process is reversed on a sloped roof: it’s the heat escaping from inside that creates the pattern. A poorly insulated attic warms the roof deck, causing snow to melt midway down the slope, and the water then refreezes at the roof edge. This is exactly how ice dams form—a phenomenon for which CAA-Québec recommends a zero-tolerance policy, given how costly the associated water damage can be.
Weather conditions determine the quality of the survey—long before the equipment does.
When to Perform a Thermal Imaging Inspection: Ideal Conditions
Even the best equipment on the market cannot compensate for poor weather conditions. The ASTM C1153 standard , “Location of Wet Insulation in Roofing Systems Using Infrared Imaging,” devotes an entire section to weather criteria and mandates that surveys be conducted at night.
| Condition | Target | Why |
|---|---|---|
| Time of Day | After sunset, until a few hours into the night | The roof cools down, damp areas remain warm, and the contrast becomes apparent |
| Sun exposure beforehand | Several hours of sunlight on the same day | The roof must be “charged” with energy to harness the thermal inertia of the water |
| Surface | Dry, with no snow or puddles | A thin layer of water evens out temperatures and hides everything |
| Wind | Light | The wind cools the surface randomly and evens out the differences |
| Interior-Exterior Temperature Difference (Attic) | As large as possible, typically in winter | If there is no temperature difference, no heat loss is visible |
Specifically, in Quebec, there are two ideal times: clear evenings in late summer and fall for flat roofs, and cold winter days for attic insulation and ventilation.
In winter, the difference between indoor and outdoor temperatures reveals problems with attic insulation.
Flat Roof or Sloped Roof: Two Different Inspections
On a flat roof with an elastomeric membrane—such as TPO or EPDM—the insulation is located above the roof deck, in contact with the waterproofing: this is the typical scenario covered by the standard and the one in which infrared imaging is most reliable. Moisture pockets are mapped, marked off with tape, and repairs are often limited to these sections.
On a sloped roof, the insulation is located in the attic, beneath a ventilated air space. The camera is primarily used to assess the insulation and ventilation, two parameters regulated by the Code: the free ventilation area must be at least 1/300 of the insulated ceiling area in typical cases, as noted by Écohabitation in its guide on attic ventilation. A thermal scan combined with a thorough visual inspection of the roof makes it possible to distinguish between a lack of insulation and an actual water leak.
Camera on the ground, on the roof, or mounted on a drone
The ASTM standard covers both ground-based and aerial surveys. Each approach has its place.
| Method | Strengths | Limitations |
|---|---|---|
| Handheld camera, on the roof | Maximum resolution, immediate marking of areas, on-site spot-check validation | Work at height; slow over large areas |
| Ground-level camera, from outside | Quick view of walls, cornices, and roof edges | Low-angle view; the roof surface remains barely visible |
| Thermal Drone | Complete mapping in just a few minutes—ideal for commercial roofs and hard-to-reach roofs | Requires a certified pilot and a registered drone; flight is prohibited in wind and rain |
In Canada, operating a drone weighing between 250 g and 25 kg requires the aircraft to be registered and the pilot to hold a certificate, according to Transport Canada’s drone safety regulations. This is no minor detail: an aerial thermal survey conducted outside the regulatory framework is of no value should a dispute arise. Our team ensures compliance with these requirements as part of our roof and attic thermography service.
How Does a Thermographic Inspection Work?
- Gathering background information: age and type of roof, history of leaks, blueprints, recent work.
- Selecting the right weather window: a dry, calm evening following a sunny day.
- Reference data: a few images of areas known to be sound, to calibrate the analysis.
- Complete scan: thermal image and visible-light photo for each sector, taken from the same vantage point.
- Marking of anomalies directly on the roof, with measurement of dimensions.
- Minimal destructive validation: core sample or moisture test in an anomaly and in a sound area, for confirmation.
- Report: annotated map, affected areas, repair priorities.
Step 6 is the one that is too often skipped. The standard itself specifies that infrared data must be verified using invasive methods: without this validation, a hot spot may simply be a change in material or a pipe beneath the bridge.
What You Do with the Results
A thermographic report helps you make three concrete decisions. First, carry out targeted repairs: replace 20 m² of wet insulation rather than re-roofing 200 m². Second, address the root cause: if heat loss is the primary issue, the problem lies in the attic, and the real work involvesinsulating the roof and attic, not the roof covering itself. Finally, document the work: dated before-and-after images provide solid evidence for an insurer or a future buyer.
When it comes to energy, the issue is far from theoretical. The Quebec government ranks insulation among the most cost-effective measures for reducing a home’s energy consumption, as detailed in its fact sheet oninsulation, airtightness, and ventilation, and heating accounts for the lion’s share of residential energy bills, according to Hydro-Québec. An attic brought up to current energy-efficiency standards in the Building Code pays for itself over the course of a few heating seasons, not decades.
Things to Know Before Paying for a Statement
Thermography isn’t magic. It doesn’t work on a snow-covered roof, in the rain, or at noon during a heat wave. It cannot penetrate a membrane weighted down with thick gravel, nor a highly reflective metal roof, whose emissivity skews the measurements. Nor does it replace a hands-on inspection of flashings, seams, and drains.
Let’s add another common pitfall: condensation. Many issues attributed to a leak are actually moisture generated indoors that migrates into the attic. Before jumping to conclusions, you need to rule out this possibility, as we explain in our article on howto prevent condensation in the attic.
Frequently Asked Questions About Roof Heating Cables
Can roof thermography detect an active leak?
It pinpoints moisture trapped in the insulation, not the exact point where water is entering. The ASTM C1153 standard makes this clear: the method does not determine either the cause or the point of entry. It is used to identify the areas that need to be opened up.
How often should a thermographic inspection be performed?
For a commercial flat roof, an inspection should be conducted every three to five years, and after any major event (hail, storm, roof work). For a single-family home, an inspection is generally reserved for specific concerns: stains on the ceiling, unusually high heating bills, or recurring ice dams.
Does it need snow or cold weather to work?
No. A snow-covered roof is actually the worst-case scenario. Cold weather is only helpful for analyzing attic insulation because it creates a significant temperature difference between the inside and outside.
Is a drone inspection as reliable as an on-site inspection from the roof?
To quickly map a large area, yes, and it’s often safer. But final confirmation requires an on-site inspection of the roof and a moisture survey of the marked areas.
Does my insurance cover the damage that was discovered?
It depends on the cause and your policy. Sudden damage resulting from a covered event and gradual wear and tear are not treated the same way. Dated thermal images, along with the report, remain the best supporting documentation to include with a claim.
Have concerns about your roof?
A properly conducted thermal inspection costs a fraction of what a roof replacement would, and it prevents you from having to open up your roof unnecessarily. If you notice a stain on the ceiling, a damp attic, or recurring ice dams, talk to our team: we’ll first verify what the camera reveals, then provide a quote only for the work that’s actually needed. Contact us to schedule an inspection.
