You have to see everything because a thermal image alone can fool you.
It wasn't a cold day out, about 45F. And it was cloudy.
Breaking out Mighty Mo to do the thermal image sweep of the insulation in the house, this is what the ceilings looked like on the upper level.
The roof rafter joists are visible as the purple lines, with the insulation filling the gap between.
The temperature difference between the insulated areas and the wood joist rafters is not very different.
Does this appear to be a well-insulated space?
To know for sure you have to look into the attic space!
Does that look like a good amount of insulation?
It is not.
This house was built in 1954 and the original insulation was a thin layer of mineral wool typical of the era.
While mineral wool is a very good insulator, this thin layer does not provide much of a thermal barrier, with little R-value.
The tops of the roof joist rafters can be seen.
On top of the mineral wool the homeowner at some point laid a layer of cardboard down, ostensibly to improve the insulation in the attic. When I don't know, but there was newspaper on top of the cardboard dated 1980, so apparently the cardboard preceded that.
However, from the thermal image alone one might think the insulation was plentiful and well placed.
Instead we found a consistent thin layer of mineral wool with cardboard on top.
What is the thermal R-value of cardboard? About .25.
My recommendation: thermal imaging requires that one look at the big picture. All of the facts must be investigated to help determine if the thermal image seen is the complete picture. Moisture cannot be determined without a moisture meter. Missing insulation cannot be determined unless one looks at what is happening on the other side. And so it is with this attic space. While the thermal image looks to be consistent and perhaps indicating good insulation, the fact is that the image is simply reporting a consistent layer of covering. I expect in very cold weather these rooms are cold and in very hot weather these rooms are uncomfortably warm because the insulation above is not very good!
Jay Markanich Real Estate Inspections, LLC
Based in Bristow, serving all of Northern Virginia.
Office (703) 330-6388 Cell (703) 585-7560