Reduces Likelihood of Mold in Walls

Another benefit of spray foam insulation is that it reduces the likelihood of mold in your walls.

I've seen a number of renovations where the contractor opened the walls and found mold all over the batt insulation in the wall cavity.  The first question is "how did that get there?"  You would think it would be hard for mold to form in what you and I would consider a closed environment.

What ends up happening in a wall with batt insulation is what's called a "thermal loop" occurs.  A thermal loop is formed when air close to the outside of a wall heats up (due to higher exterior temps) and rises, transfers closer to the interior face of the wall assembly, cools off (from the interior conditioned temp), and falls within the wall.  It actually forms a loop of air transfer within the wall cavity.  Again, the air heats up and rises, cools off and falls. 

Warm air holds more moisture than cool air. And when that warm, moist air comes in contact with a cooler surface, the moisture in the warm air transfers to the cooler surface as condensation.  Condensation occurs, which contributes to the formation of mold within the wall.

Please google thermal looping to learn more about it.

What you come back to is that when you spray foam insulation in your wall cavity, not only do you keep air from moving around within your wall cavity (and thus, significantly reducing the probability of mold forming), but you also eliminate the temperature variances that cause thermal looping in the first place.  The transfer of heat from the outside of the wall assembly to the interior of the wall cavity never occurs to begin with.