Insulation of non-conditioned space

[sedesigner06]

I have a pre-engineered metal building that I am doing construction management on. The question was raised why the building was not insulated to prevent condensation. It is my understanding/belief that if the area is not heated or cooled the temperature difference between the interior and exterior should not be great enough to develop condensation. The building is located in Midwest (St. Louis, MO) as a reference.

Does anyone have any experience in the requirement of roof insulation in not conditioned spaces or any article that may help?

Thanks!

 

[Archie264]

To understand the topic this video is well worth the 75 minutes it takes to watch it. Link After watching it you'll never quite look at buildings the same way.

[Edit:] Per Lstiburek the keys to understanding the issue are:

1. Understanding that moisture moves from hot to cold.
2. Knowing that, put the insulation in a location that will not cause there to be a thermal break on the indoors side of the vapor barrier.
3. Knowing that, putting the insulation on the outside of the vapor barrier will always work.

But please watch the video and let him speak for himself. This is not my field and you would be ill-served relying on my understanding of what he said.

 

[XR250]

It really just comes down to the relative humidity of the air inside the building. The metal roof can radiate to the clear night sky and can get cold enough to condense the moisture. Is that going to be a problem?

 

[sedesigner06]

Condensation is not idea but also not the end of the world. My suggestion is that it is not worth it for our scenario, just wanted to see if could get some additional input/information.

 

[Archie264]

I would agree. If it's neither heated nor cooled then I imagine it has plenty of ventilation and with nothing to trap the condensation in place then it will find it's way out easily enough, same as with a car port, barn, etc.