Thermography in Home Inspection: What It Reveals

A home can look flawless to the naked eye: fresh paint, smooth drywall, clean floors. Yet behind those surfaces, water can be building up, insulation can be missing and cold air can be leaking in with every gust of wind. At Boreon, infrared thermography is part of every inspection, no exceptions. Here is why, what it actually reveals in Greater Montreal buildings, and, just as importantly, what it cannot do.

Why the eye isn’t enough

A visual inspection relies on what can be seen: a water stain, a crack, a failed seal. The problem is that many building envelope defects leave no visible trace until they are advanced. A slow leak behind a freshly painted wall, settled insulation in an attic or an air leak around a new window go unnoticed during a walkthrough. By the time the stain finally appears, the damage is often done.

Thermography adds a layer of information: it shows how heat moves across the surface of walls, ceilings and floors. That information then guides our follow-up checks.

How it works, in plain language

Every object emits infrared radiation, invisible to the eye, whose intensity varies with its temperature. A thermal camera captures that radiation and turns it into an image in which each colour corresponds to a surface temperature.

Two concepts matter for reading these images correctly:

Emissivity: a surface’s ability to emit its radiation, on a scale from 0 to 1. Painted drywall emits well; shiny metal emits poorly and behaves more like an infrared mirror.
Apparent temperature: the camera receives both the radiation emitted by the surface and the radiation it reflects from its surroundings (a person, a lamp, the sky). The value displayed is therefore an “apparent” temperature that must be interpreted by someone trained. A reflection, for example, moves when you move; a real defect does not.

Above all, remember this: the camera does not see through walls. It measures the surface. What happens inside the wall (moisture, missing insulation, air leakage) only shows up if it changes the temperature of that surface.

What thermography reveals

Moisture and water infiltration

A wet material cools through evaporation and does not behave thermally like a dry one. A damp area often appears as a cooler patch with irregular edges, for example under a window, at the base of a foundation wall or on a ceiling below a bathroom.

Missing, settled or displaced insulation

In winter, a poorly insulated cavity shows up as a sharp cold area on the interior wall, often shaped like the bay between two studs. In a ceiling, loose-fill insulation that has settled or been pushed back along the attic perimeter creates cold zones along the exterior walls.

Air leaks

Air leaks leave characteristic streaks or tongue-shaped patterns around windows, doors, outlets on exterior walls, rim joists and wall-ceiling junctions.

Thermal bridges

More conductive elements that cross the insulation (studs, lintels, concrete balcony slabs, joists) appear as regular lines. This is not always a defect, but it is an energy loss and sometimes a cold spot where condensation can form.

Roofs, radiant floors and plumbing

On a flat roof, wet insulation holds heat longer than dry insulation and stands out after sunset. Indoors, the camera can also trace a radiant floor layout or locate a leaking hot-water line in a slab.

A bonus: electrical hot spots

An overheating breaker, connection or cable may stand out in the image. We report it when observed and recommend evaluation by a licensed electrician; this does not replace a specialized electrical inspection.

What we find in Montreal’s housing stock

A few typical situations that thermography helps bring to light:

Older plexes: masonry walls with little or no insulation, air leaks at the rim joists between floors, flat roofs with wet insulation after years of successive repairs, infiltration around replacement windows.
Condos: thermal bridges at balcony slabs and slab edges, air leaks around patio doors, signs of moisture under windows or on ceilings coming from a neighbouring unit.
Bungalows: insufficient or displaced attic insulation, ceiling air leaks (attic hatch, recessed lights), finished basements where foundation moisture is hidden behind drywall.

In every case, the thermal image does not make the diagnosis alone: it tells us where to look more closely.

Conditions for a reliable reading

Building envelope thermography relies on a temperature difference between inside and outside. Reference standards, including ASTM C1060 and ISO 6781, generally call for a difference of at least 10 °C across the envelope; Canada’s National Master Specification (NMS) even requires 15 °C for this type of work. That is why the Quebec winter is a natural ally.

Season: cold months produce the most telling images. In warm weather, the difference is smaller and we adapt the method (time of day, air conditioning, more cautious interpretation).
Sun: a sun-exposed facade stores heat that masks defects for hours. We favour shaded walls or readings outside direct sunlight.
Wind: it cools exterior surfaces and blurs exterior readings, but it also accentuates air leaks seen from inside.
Rain: a wet surface cools through evaporation and can distort exterior readings.

When these conditions are not met, we say so in the report rather than over-interpret an image.

Limits, and how we confirm

Thermography is a screening tool, not a verdict. A cold patch may be moisture, but it may also be an air leak, a reflection, a change in material or a recently moved piece of furniture. That is why every anomaly is verified:

Moisture meter: a moisture reading in the material confirms or rules out the presence of water.
Visual inspection: we look for the likely source (flashing, caulking, plumbing, grading).
Context: weather, wall orientation, building history.

To pinpoint air leaks, thermography can be combined with an airtightness (blower door) test: by depressurizing the house, outdoor air is drawn in through every opening, making leaks far more visible to the camera.

Roof thermography

For flat roofs and commercial buildings, the reference method is ASTM C1153, which covers locating wet insulation with infrared imaging at night, from the ground or from the air (drone). It identifies wet areas but does not, on its own, determine the cause or point of entry: on-site verification is still required. Learn more in our article on commercial roof thermography under ASTM C1153.

Why Boreon includes it in every inspection

Elsewhere, thermography is often sold as an add-on. At Boreon, it is built into every pre-purchase inspection at no extra cost. The reason is simple: our specialty is the building envelope, roofing and mechanical systems, and that is exactly where thermography is most useful. Our team brings together technicians, InterNACHI-certified inspectors and an engineer who is a member of the OIQ for expert assessment mandates. For a targeted need (energy efficiency, leak investigation, construction follow-up), thermography is also available as a dedicated mandate.

What you get in the report

Thermal images of the anomalies, paired with a standard photo of the same spot;
A clear explanation of what the image shows and its likely interpretation;
The results of confirmation checks (moisture meter, visual observations);
The survey conditions (outdoor temperature, sun exposure) and their limits;
Practical recommendations: monitor, have it corrected, or have it assessed by a specialist.

FAQ

Can a thermal camera see through walls?

No. It measures surface temperature. A problem inside the wall is only visible if it changes that temperature, which is why confirmation with a moisture meter and a visual inspection matters.

Can thermography be done in summer?

Yes, but the temperature difference is usually smaller and results are more limited. Standards aim for a difference of about 10 °C; winter offers the best conditions. We always state the survey conditions in the report.

Does a cold spot always mean moisture?

No. It may be an air leak, missing insulation, a thermal bridge or simply a reflection. A moisture meter reading is what confirms the presence of water.

Does thermography replace a blower door test?

No. A blower door test measures overall airtightness; thermography helps locate the leaks. The two complement each other very well.

Is thermography really included in your pre-purchase inspection?

Yes, in every inspection, at no extra cost. It is not an option at Boreon.

Buying a property? Request your pre-purchase inspection quote: thermography is included.

Case study

Real example: on an industrial flat roof, thermography tied leaks and rising energy bills to a single cause, wet insulation. Read the case study →

Thermography: what the camera reveals that the eye cannot see