Lets get it on

Ok guys flat roof ice standing 10:00 AM clear no wind why is this temp reading 7 degrees on the ice E-setting 70

Reflection from the sun.

Colder areas are shaded from the sun.

Reflection of the sky.

All reflective surfaces will read the surrounding temps (at some point on them depending on their shape) rather than their temp.

Example: Watch out for breaker panel terminal lugs, they look hot because of your body heat.

Yup, and most will look hotter than others but you must actually go by the actual temperature of the area in question. If you see a thermal image of a breaker reading a temperature of 110 degrees, it may not be a problem verses seeing a breaker hot spot at 210 degrees.

Your e-setting for this application is too low.


New shiny conduit looks hot too. It fooled me the other day when I was showing a builder my cam.

Reflection of the sky.

All reflective surfaces will read the surrounding temps (at some point on them depending on their shape) rather than their temp.


Exactly!! That’s why roof (inspections)scans should be conducted in the evening.

Attic door, colder in the attic than in the house.
Where is the hot spot coming from?

My reflection. :slight_smile:

Why is that?
The sky is the same temp, day or night (if it is clear and low humidity)?

You tell me Dave. If you are conducting a roof moisture survey why would you do it in the daylight.
Would it not be better to do it after sunset? This will eliminate reflections,shadows and allow you to detect roof moisture. But you already know this stuff you are Level 3!!

The thermal window is open the widest in the early morning or late afternoon/early evening. It is typically at its most narrow margin at high noon. As water has a high thermal capacitance, the chance to observe moisture on a flat roof is at its greatest potential in the mornings and evenings especially with a less sensitive camera.

I am seriously asking you.

There are many good reasons to do roof scans at night. As you posted.

My question is why in this case would the ice show up differently at night?

Thank you Mr. Warner.

I was taught a method of determining the maximum Delta T by monitoring the temperature of the roof and the temperature of water in a container. In the morning you’ll receive the greatest temperature difference as the roof begins to warm more rapidly than the water. At some point around midday, it is likely that the water temperature will match that of the roof temperature. Later in the evening the roof will cool more rapidly than the water. At some time late at night, just like at high noon the temperature of the roof and the water will equalize.

Guys this was not a test I was surprised my self when the low temp showed up I was not actually scanning the roof was the wrong time of day especially with the water frozen. And yes my instructor did say the night time after radiation cooling takes place never scan a roof in the heat of the day. you are looking for evaporation of the water beneath the roof covering; water holds the heat longer and will show up.

Yes I did have the wrong E setting I just happen to have the camera in my hand when I went on the roof as I had been called to check an interior wall which I will post later I just wanted to view the roof before I went inside. Just forgot to change the E-setting for the roof. The outside ambient was in the low 30’s when I snapped that IR pic. But that still does not explain 7 degrees as nothing in the area was that cold. When I am just playing with the camera I will often change the E-setting just to see the variances in the temps.

As for the breaker temp being discussed my instructor stated the allen set screw hole will create a reflection or cause the actual temp to be off and has to be adjusted for. There is a specific name for this and I can not recall the name without going back to my books. I was not jacking with any one don’t have a clue why the temp in the pic was so low. I am open for serious discussion.

Great discussion .
Brings back what we where taught and gets us all thinking ,
Thanks to all… Cookie
The instructor said to me less then 2 % of those who buy a camera take classes .
Now some I expect have Plant instruction as in our class 22 only 4 where Home Inspectors.
I wonder have all Home inspectors taken classes or Just the NACHI members ?

I suppose monitoring a container of water would help but seems a bit extreme than just understanding the thermal window. I was trained that flat roof inspections and EIFS inspections should be conducted in early morning or evening for the same reasons (thermal window). You are precisely correct about the thermal differences at the times of day. Water signatures will appear as a cool spot in the mornings and a warm spot in the evenings but may become “invisible” to the camera midday or late at night.

I suspect part of it is indeed reflection from the sky and space but your image indicates a temp range from -12 to 28. There’s some awfully cold objects up there on that roof. You don’t indicate ambient temp or the lowest temp of the night before. The low temp is probably due to the thermal capacitance of water and also due to latent heat of fusion. Also understand that air movement at 10MPH a surface will lose 50% of its actual temp. The slightest breeze will reduce surface temps.

Spend that much money on a piece of equipment and not know how to use it or at minimum the science behind the technology!

Dave, is that a reflection from the termination strip used on the carpeting?