False positives

One of my biggest problems are the false positives I get from insulation issues. In cathedral ceilings, there are areas around the trusses that are hard to seal off with fiberglass batts only. These areas are frustrating as they show all over the ceiling. Prior water damage is another as the fiberglass never returns to the pre-wet condition. Did a house that near every lower chord, gusset and diagonal brace it showed cold, like it was wet. None were wet, the roof was new and when asking the owner, the ridge vent had been leaking. I determined that the water was running along the upper chord, hitting diagonal braces, soaking the insulation that would compress it to allow heat to escape. Of course I could not see it to verify. Would this be likely or is there something I am missing. I hate to assume things, but would not even had a reason to think about it without the camera. I would not even know there was anything to worry about!:shock:

Got any pictures Ralph?

Linas, sorry about the delay. These pics have a small span to get the result. The clarity is poor when yougo from 648KB to 28KB.




Not always false. Remember, the camera shows HEAT, not WATER.

Cold areas CAN be water intrusion or leaks, but not always. Back it up with a deep probing water meter, ALWAYS.

Cold is not always a defect, just an indication.

Check this out. Exterior wall. What is the cause of the two cold spots?

Answer to follow once some guess.

On second thought, seems that my label gave this away.

Light fixture interior normal.jpg

light fixture interior IR.jpg

Could it possibly be air infiltration around the exterior light and light switch???:stuck_out_tongue:

You got it. Bottom was the interior light switch. The top one was an exterior light box. Cold air infiltration but no moisture.

Remember, cold means cold. If you suspect moisture. use a moisture meter.

Hope this helps;

Will is absolutely correct. Potential “false positives” are part of almost every inspection. As Will said, they are not really false positives, they are thermal anomalies that could be moisture, or could be other things. It is worse in the winter with regard to temperature anomalies that COULD be moisture. I end up carrying a moisture meter around with me through the whole house to double check all the air infiltration anomalies that are questionable. It is a little easier in the summer with regard to finding moisture, but you can still get cold spots from HVAC ductwork leaking. With experience you will get a feel for the way moisture looks and the “normal” places that you find air infiltration, but it still requires a lot of double checking.

And then we can make things more complicated by bringing in “Condensation” issues, which can be both moisture and air infiltration (cold causes high moisture readings as a result of condensation).

A “False Positive”; An incorrect result of a test which erroneously detects something when in fact it is not present.
You are not seeing a false positive because it is in fact there.

I don’t really care for the term “false positive” as David has stated but it looks like in one of those photos you’re possibly looking at t-bridging from drywall fasteners close to the surface and a tie plate on a truss.

My best advice is to get used to picking these things out or you’re going to be chasing your tail on every inspection. What your seeing most of the time with your camera is normal stuff…you have to learn what normal looks like. I’d also advise against using different palettes or excessive image manipulation to highlight anything. Most of the time, moisture will stick out like a sore thumb.

When dealing with insulation, especially fiberglass, some of the delta-T’s are simply the result of improper installation by installers. Many times its air pockets or simply compressed, under insulated areas or simply where insulation has fallen away from the wall cavity, especially in cathedral ceilings.

Having a keen knowledge of building principles and common practices will go along way in helping one understand what they are truly looking at, especially when dealing with insulation and framing applications.


The diffuse edges around these areas are not typical of moisture. Moisture will typically give you fairly sharp, well defined, edges like what you see below.

Thanks for the feedback folks. This is a real learning process. People think you just look and report what it shows! How wrong that is!