Interview Suggestion: George P. Swanson
Dave absolutely has to interview George Swanson. He, and the people he works with, have solved the problem of mold in homes by extensively researching vapor permeable building techniques.
How long does mold need to grow on wet surfaces before it becomes unhealthy? Most experts say all it takes is 24-48 hours for mold to get to spore formation, which is considered the point of no return.
Studies show that up to 50% of modern walls with fiberglass insulation and plastic vapor barriers have water problems, meaning they have mold growing within them. That is a huge, and costly, problem and shows the failure of modern walls to keep us healthy. Unfortunately the paradigm of building tight may work on paper, but it is flawed when implemented in the field. This is because you never achieve the 100% air-tight and vapor-tight wall you designed in the first place. Plus, the tighter you make the wall, the greater the pressure exists for vapor pressure to equalize on both sides, driving more moisture into the wall. So you can exacerbate the problem. Ultimately you are left with the reality that when a "tight" wall fails, it fails in a big way.
We say instead, design a wall to be thermally insulating, meaning keep warm indoor air from leaking to the outside, but allow any moisture vapor or rainwater that seeps into the wall to move out. The wall can then dry out within the 48 hours needed for mold to grow.
Our motto is, make walls "waterproof but vapor permeable." We accomplish this with our envelope materials and the natural, "breathable" finishes we use.