Is this because of no ventilation?

I did a Thermal scan for this client, and when I got to her attic space I found there to be about 16"-20" of blown in insulation in places. She had it installed because she has a hard time keeping the 2nd floor cool in summer and warm in winter.

So the insulation installers came in and blew in gobs of insulation to try and help this. I noticed what looked like moisture on the roof rafters and decided to look at them with the TI. Hard to get a good shot because it was 120+ in the space and nowhere to go.

So, long story short, there is no venting in the attic, the roof is a gambrel style, there are vents at the bottom of the bottom roof, but with all the insulation that was blown in, if the soffit vents were working prior, they are not now. Even if they did, there is not place for it to exhaust.

Now my question, the moisture noted in the rafter, is this due to condensation because the insulation is packed in there, she said her roof is new (I don’t know how new) so I am assuming it is not leaking. If you notice, the one to the right is the same way, but not as severe.

Everybody’s thoughts are welcome.



Do you have digital images to share?

How was the moisture verified?

Digital image is not of much use, but here it is.

I did not get inside to confirm with MM, but visually it looked like a problem which is why I decided to IR it.

I am assuming it is moisture based on the thermal signature. I know, I shouldn’t assume, but there really was no safe way to get to the spot.


Had AC been running?

Yes, ducting is a minimum of 3’ away from this point and the register would have no effect on it.


I was not there to see what you saw, but from the pictures I can’t really make out anything significant. First, it looks like you adjusted your IR image before uploading, correct?

If you have the original image (without post processing), then upload so I can take a look at it.

The dark blob in the middle of the IR image (I believe this is what you think is moisture), could be just a cooler pocket near the rafter.

Did you have your camera in auto or manual mode?


Hi Kevin,

I do not have the original. If I make adjustments, I change the level and span and delete the target and save the image. I use it primarily for relative temperature and heat signature. The dark spot in the middle is just about 6 degrees cooler than the substrate which would most likely be moisture given the pattern (as they tought us in class). It was in manual mode and the dark spot is actually on the rafter and goes up on the roof sheathing as well. (bad digital photos or lack there of, lesson learned here)

For arguements sake, if this is moisture, is this a good example of what happens when the insulation is in contact with the roof sheathing?


At 120 degrees you are not going to have any condensing moisture in the attic. Dark colors in the wood can be the wood density, not moisture. The big blob looks like air exfiltration from indoors. Really not much to go on. Get the dew point for that date/time from the national weather service. I am sure it was not 120. You could have a water leak, need weather info, but condensation is not likely without air exfiltration.

This is where I was headed…cooler pocket, potentially.

Thanks David,

I understand there will not be condensation at 120, however, it was only about 50 the night before and we just came out of winter not too long ago. We had all winter for condensation to build up and saturate the rafter and sheathing (isn’t this one of the things we look for in attics? the IR doesn’t change the building characteristics, just what we can see) which may not dry by 11am even at 120, could that have been caused by the insulation being in contact with the sheathing? or can somebody tell me that condensation does not occur in a situation like this.

FYI-I am fairly certain it is moisture because the rafter and sheathing had some visible deterioration.


Originally Posted by dandersen
*At 120 degrees you are not going to have any condensing moisture in the attic. Dark colors in the wood can be the wood density, not moisture. The big blob looks like air exfiltration from indoors. Really not much to go on. *

Point understood.


The dark colors in the wood from moisture can be from winter.

Right now you have A/C air going into the attic, in the winter it will be humid interior air condensing on the cold roof.

You will not have moisture hanging around for more than a few minutes in 120 degree.

You have had some serious heat up there, you have nothing left over from winter.

Insulation prevents air movement.
Insulation against the wood is not going to cause problems.

My former life was about psycrometric evaluation of air properties.
Give me the date and time and I will tell you for sure if it could happen.

Air infiltration/exfiltration is the greatest source of heat loss/gain from the interior of the house. Being cold in winter and hot in the summer, plus the attic ventilation issue along with this cold spot (which looks like air) would sum it all up.

This is what cool and hot air looks like through insulation.

OK David,

So, I understand the insulation and its purpose, in many circumstances when there is insulation against the roof decking, it gets called out as being a point of concern. Would this be the case ONLY when there is soffit venting involved and insulation is restricting the flow/venting and if I understand correctly what you are saying here is, becuase the insulation is against the wood it is stopping air flow so therefor there would not be condensation?

If my IR photo is showing exfiltration, would the pattern really be as smooth and consistant as it is? and why would it only be 6 deg. different, which is the maximum temp. diff. there would be with moisture vs. substrate?

Just questions and trying to learn.


Deep blue or black (on the iron palette) DOES NOT MEAN MOISTURE. It means (relatively) cooler. ALWAYS back up with a deep probing moisture meter.

In any case, the attic is not properly ventilated. Call that out.

I see many cold spots that are not moist.

Cold spots, that are also moist, in attics, are usually seen only in colder weather.

Hope this helps;l

Come on Will, why did I buy the dang camera then?:shock::mrgreen: anyway, if the dark did mean that, we would all be Hero’s to our clients.

I posed the question to find what you all think and have for thoughts on this because I could not get in there to put a MM on it to confirm.

I will keep watching for more.


Possibly?? I would at least call out the lack of baffles, but would not say that this is moisture just going off the discloration in the rafters.

Be careful when drawing conclusions that you cannot back up. I’m sure you know from your training that verifying suspected moisture is an absolute must.

At the very least, you could say something like this:

“Atypical thermal anomaly noted in a section of the _______ in the attic. The thermal patterns and the discoloration of the rafters are consistent with moisture or possible moisture intrusion. However, the moisture content of the insulation or the wood rafter could not be verified due to insulation that would make mobility hazardous. It is recommend that a QUALIFIED Contractor evaluate further.”

But, I try and stay away from calling out possible moisture related issues unless I have verified with a moisture meter or other means.

Terms like “is consistent with”, “increase the potential for”, or decrease the potential for" are effective ways to describe “uncertainty.”


Hi Kevin,

I was thinking along those terms myself, I certainly would not make such a statement without being able to back it up, however the lack of ventilation goes without saying.

I do like the descriptive paragraph though, thanks.

Agreed. It is better to say what you do know and what you do not know.

What I would tell my client in this case is that the highest probability is that this anomaly is a air exfiltration. However, I was not able to confirm that as fact due to the limitations, in accessing, the location. I recommend removal of this section of insulation and temporary flooring installed to provide safe access to the location to visually confirm findings/ and/or perform additional testing and observation.

Summary: you give your client an opinion that is worth something, you tell them the truth, give them some potentials, and tell them it requires additional action.

Good thread.

I had these this morning. No access. Moisture tested negative with meter. Just have no idea because I can’t get to it from here.

No reason to “make something up” or head down a road without supporting evidence. They can monitor it, and if something shows, we know where to look.

After all, no one else could tell them that it exists! It’s invisible! At least I tried.

I have my suspicions. The chair area “used to be” a garage. They added on several times to the house. Insulation (that is no longer needed because it is now an interior wall) was likely removed and the camera sees the “difference”!

I tried switching to heat to see if it turned hot. Suspecting an air duct leak. Nothing changed. I suspect cooler air from the basement is getting part way up the wall.