Key takeaways
- A thermal image records surface temperature, so it points to where heat or moisture may be moving through a wall, but it does not measure the insulation itself or prove the cause of a pattern.
- The conditions at the time of the scan decide whether the picture means anything, so a scan taken without a recorded temperature difference and recorded weather is an image that cannot be defended later.
- A cool band that follows the framing, or a warm patch at a gap, is a reason to investigate, and it should never be written up as proof of a defect on its own.
- A scan is most useful when it is paired with a physical check, such as opening a small inspection point, testing moisture or looking at the insulation as installed, and the two are recorded together.
- A scan with its conditions, its date, its interpretation and the follow-up checks recorded is evidence a certifier, an owner or an engineer can rely on, while an image saved without them is an argument waiting to happen.
A thermal camera is one of the more impressive tools a builder can carry. It turns the invisible into a picture, and a wall that looks finished can suddenly show bands, patches and stripes that the eye could not see. The temptation is to treat the picture as the answer. A cool band is missing insulation, a warm patch is an air leak, and the report is written and sent before anyone has checked the wall. That is the habit this article is written against.
The camera is useful because it finds places worth investigating. It is weak when it is asked to prove what is behind a surface. An infrared image records how warm or cool each surface is at the moment of the scan, and the surface temperature is affected by many things that are not the insulation or the moisture at all. The wall is only the start of the question, and the answer comes from the checks that follow it.
This article covers what an infrared image measures, why the conditions decide whether the picture means anything, what a scan can and cannot prove about insulation and moisture, and how to pair the scan with physical checks and dated records. It does not cover the general insulation gaps or the detailing of walls, which have their own articles, and it is written for the builder who wants to use the tool without over-reading it.
What an infrared image actually measures
A thermal camera measures the infrared energy coming off a surface and converts it into a temperature. The image is a map of surface temperatures, colour coded so that warmer and cooler areas stand out. It does not look through the plaster, the cladding or the insulation. It sees the face of the material, and the face is affected by what is behind it, by the air moving across it and by the sun, the wind and the material itself.
That is the first limit to hold in mind. Two walls with identical insulation can show different pictures on different days, and two walls with different insulation can show the same picture on the same day. The camera is recording the surface, and the surface is a product of many influences at once. The skill is in separating the influences, and the scan alone rarely does that.
Surface properties matter too. A shiny or reflective surface can reflect the temperature of something else in the room, and a wet or damp surface can cool through evaporation in a way that has nothing to do with the material behind it. The reading is only as reliable as the reading of the surface, and the operator has to think about what the surface is doing before deciding what the image means.
Why the conditions decide whether the picture means anything
A thermal scan depends on a temperature difference across the wall. Without a sustained difference between the inside and the outside, the wall does not show the heat flow that the scan is supposed to reveal. A scan taken on a mild day with the building in equilibrium will show very little, and a scan taken straight after a hot afternoon will show the sun rather than the insulation. The conditions have to be right for the picture to be informative.
The conditions also have to be recorded. The date, the time, the outside temperature, the wind, the sun on each face of the building and the inside temperature all change how the picture should be read. A scan without those details cannot be checked later, and an image that cannot be checked is an image that cannot be defended. A certifier or an engineer who receives a scan with no conditions will have no basis for accepting it, and the builder who produced it will have to explain a picture that cannot be explained.
Build the conditions into the routine. Keep a short form on the phone or the clipboard, fill it in before the first image, and attach it to the scan. The few minutes it takes are the difference between a useful record and a picture that is simply an opinion.
What a scan can show about insulation and air movement
Used under good conditions, a scan can show places where the wall is behaving differently from its neighbours. A cool band that follows the line of the framing may suggest that heat is passing through the framing where insulation was expected to stop it. A warm or cool patch at a joint, a corner or a penetration may suggest that air is moving through a gap. Patterns that repeat across the wall are worth investigating because they usually have a common cause.
These are useful clues, and they point the investigation at the right place. The insulation guidance from the Australian Government sets out why the insulation matters for the performance of the building, and the scan is a way of checking whether the insulation is doing what it was installed to do. It is a check on the performance of the wall rather than a count of what has been put in it.
What a thermal scan can show, and what it cannot prove
| What the image can show | What it cannot prove |
|---|---|
| A cool band that follows a stud line | The thickness or performance of the insulation behind it |
| A warm or cool patch at a gap or a joint | Where the air is coming from, without a physical check |
| A surface colder than its neighbours | Whether moisture is inside the material, or how much of it there is |
| A pattern that repeats across a wall | The cause of the pattern on its own |
| A hot spot at an electrical fitting | Whether the fault is safe to leave without a qualified inspection |
| A reading taken under recorded conditions | Anything about a wall scanned in conditions that were never recorded |
The table above is the one to keep in front of you. The image is good at showing where to look. It is weak at saying what is there, and it says nothing at all about the thing the builder is most often asked about, which is whether the work was done to the standard the client paid for. That question needs the physical checks, and the scan is only the reason to make them.
What a scan cannot prove
A scan cannot prove the thickness or the performance of the insulation. It records surface temperature, and it cannot tell whether the material behind the surface is the thickness specified, the product specified or installed without gaps. A cool band behind new plasterboard may mean the insulation is missing, compressed, displaced or simply cooled by a draught that is not related to the insulation at all. The picture does not say which.
A scan also cannot prove the cause of a pattern on its own. A cool band may be missing insulation, a thermal bridge, a draught, an air path behind the lining or a feature of the construction that the designer intended. Without a physical check, the cause is a guess, and a guess written up as a finding is the most dangerous output a scan can produce. The report that says the wall is uninsulated when the wall has insulation in place is a report that will be challenged, and it will be challenged successfully.
The scan cannot prove that a wall is compliant either. A wall can show a clean image and still have a defect that matters, and a wall can show a bad image and still meet the design. The image is evidence of a pattern, and compliance is a question about the work as built and the documents that describe it.
Moisture: why a cool patch is a question, not an answer
A cool patch is often treated as a sign of moisture, and sometimes it is. A wet area of a wall cools through evaporation and through the greater heat it takes to warm wet material, and a scan can show that. But a cool patch can also come from a draught, from a thermal bridge or from a surface that has been cooled by a heater on the other side. A dry patch can conceal moisture inside a material if the surface has dried while the core has not.
The reliable way to test moisture is a physical test. A moisture meter, an inspection point and a look at the material behind the surface will tell you more than the image will. Record the readings with the scan, so that a later reader can see both the pattern and what was found when the pattern was checked. A cool patch that turns out to be dry is still useful, because it shows the scan was investigated rather than acted on blind.
A worked example: the cool band behind new plasterboard
Consider a builder in the inner west who had finished the lining of an external wall in a renovated terrace. The owner asked for a thermal scan before painting, because the rooms felt cold in the evenings. The builder hired a camera for the day, scanned the wall and found a cool band running along the top of the wall, close to the ceiling line. The image was clear, and the builder wrote up a note that the insulation at the top of the wall appeared to be missing.
The owner passed the note to an engineer, who asked for the conditions at the time of the scan. The builder did not have them. The scan had been taken in the early morning after a cold night, with the wind up and the sun not yet on the wall, and no inside temperature had been recorded. The engineer would not accept the note as evidence of missing insulation, and asked for a physical check.
The builder opened a small inspection point at the top of the wall. The insulation was in place, but it had slipped and was compressed where it met the top plate, and a gap had been left at the junction with the ceiling. The air path through the gap explained the cool band better than missing insulation would have. The fix was to re-seat the insulation, seal the junction and re-scan the wall under recorded conditions. The second scan showed the band had gone, and the second report was accepted. The first report would have sent the builder to add insulation that was already there.
The mistake that costs the most. Writing a scan up as proof of a defect, or as a clean bill of health, without the conditions or a physical check. The image is an indicator, and the report that states it as a conclusion becomes the document that is challenged, usually at the point where the cost of the wrong conclusion is highest.
Recording the scan so it stands up later
A scan is only as good as its record. Each image should be saved with the conditions at the time, the camera settings, the area covered and the name of the person who took it. The interpretation should be written separately from the observation, so that a reader can see what was seen and what was concluded from it. The physical checks should be recorded in the same file, with dates and photographs.
Keep the scan with the other site records, not in a camera or a phone that might be replaced. Our article on site photo record keeping and evidence covers the wider question of how images should be kept, and the same principles apply to thermal images. A dated, labelled, consistent record is the thing that turns a picture into evidence.
Pairing the scan with the physical checks
The scan should be the first step in an investigation, not the last. The routine below is the one to follow whenever a scan shows a pattern worth looking at. It takes longer than writing up the image, and it is the only way to produce a finding that will hold up.
Pairing a scan with physical checks
- 1Record the conditions firstNote the date, the time, the outside temperature, the wind and the sun on the wall before the camera is switched on.
- 2Scan the whole areaPhotograph the wall from a set distance and angle so the readings can be compared with later scans.
- 3Mark the patterns, not the verdictsNote each pattern as a question, such as a cool band or a warm patch, and keep the interpretation separate from the observation.
- 4Check each pattern physicallyOpen a small inspection point, test the moisture or look at the insulation as installed, and record what was found.
- 5Record the result with the scanKeep the image, the conditions, the physical check and the conclusion together in the job file.
The physical checks are where the builder earns the scan. An inspection point, a moisture test, a look at the insulation as installed and a check of the junctions will usually tell you more than the image did. Record what was found, whether or not it matched the scan, because a scan that was not borne out by the physical check is still a useful record of what was investigated.
Digital tools and the work health and safety side
A camera, a phone app and a shared folder are digital tools, and they carry their own work health and safety considerations. Safe Work Australia’s guidance on digital technologies covers the work health and safety side of using tools like these. A builder who sends an operator up a ladder or onto a roof with a camera and a tablet in one hand has created a hazard that the scan was not meant to address.
Plan the scan as a task, not a side job. Decide who is doing it, how they will reach the area, how the equipment will be carried and how the record will be stored. The scan is only useful if it is done safely and recorded properly, and the planning takes less time than the rework that follows an injury or a lost image.
Using the scan with the client and the certifier
When a scan is shown to a client, it should be presented as a finding to be investigated, not as a verdict on the work. The client needs to understand what the image shows, what it cannot show and what the physical checks found. A client who is shown only the picture will draw their own conclusion, and that conclusion is often more alarming than the facts support.
The certifier or the engineer will want the same things. They will look at the conditions, the physical checks and the record, and they will ask why each pattern was investigated and what was done about it. Bring the whole file, not the single image. The image is the start of the conversation, and the file is what the conversation rests on.
Keeping the scan in its place in the job
A thermal camera is a good addition to a builder’s kit when it is used with discipline. It finds problems that would otherwise stay hidden, and it gives the builder a reason to check the work before the lining goes on or the paint is applied. It is a poor substitute for the physical check, and it should never be presented as one. The discipline is to record the conditions, to investigate each pattern and to keep the picture and the findings together.
The PointCPD home page lists the NSW builder courses we offer. The tool is only as good as the judgement of the person holding it, and that judgement is worth keeping current.
Questions builders ask
Can a thermal camera tell me whether a wall has insulation?
Not on its own. A scan records surface temperature under the conditions at the time, and a cool band can come from missing insulation, a thermal bridge, a draught or the conditions rather than the insulation itself. A physical check is needed to confirm what is behind the surface.
What conditions do I need for a useful thermal scan?
A sustained temperature difference between the inside and the outside is needed, and the conditions have to be recorded with the scan. Note the date, the time, the outside temperature, the wind, the sun on the wall and the inside temperature.
Can a thermal scan prove there is moisture in a wall?
It can show a pattern that may be moisture, but a cool patch can also come from draughts, thermal bridges or heating on the other side. Test the moisture physically and record the readings with the scan before drawing a conclusion.
Should I give a client the thermal image as the finding?
Present the image as a finding to be investigated, not a verdict. Explain what it shows, what it cannot show and what the physical checks found, so the client does not draw a conclusion the facts do not support.
What should go in the record with a thermal scan?
Keep the image with the conditions at the time, the camera settings, the area covered, the name of the operator, the interpretation written separately from the observation and the results of any physical checks, all dated.
Are there safety issues in using a thermal camera on site?
Yes. Plan the scan as a task, including who is doing it, how they will reach the area and how the equipment will be carried. Safe Work Australia’s guidance on digital technologies sets out the principles to follow when using digital tools on a work site.
Sources
- Insulation · Your Home (Australian Government)
- Survey shows serious defects down in newer apartment buildings · Building Commission NSW · 2023-12-15
- Building Defects Library · Building Commission NSW · 2025-06-25
- Digital technologies and AI · Safe Work Australia
Published 27 September 2026. General information for builders, not legal, financial or engineering advice for a specific job. Check current requirements with the relevant regulator or standard before relying on them.
