What's the #1 myth regarding mold avoidance?
1. Avoid mold problems by living in a home or working in a building on a slab foundation.
Regarding slab foundations...know that in most parts of the country and the world, slab foundations have foundation walls going down to undisturbed soil and going below the local frost line. This is basically the same as a basement, except that builders fill holes created to pour the foundation walls back up with dirt. So, a slab foundation consists of a very short basement, filled with dirt.
Some parts of the country that are very warm use perimeter 'grade beams'. But these are just even shallower 'basements' with dirt inside. Water settling against a structure can get through slab foundation walls and wick up through the slab itself very easily. The phenomenon actually has a name called 'rising damp'. Concrete is very porous and acts like a sponge to wick water into itself, and often into walls sitting on it. Toilets seals and other drains that go through slabs can leak just the same as anywhere else. Ductwork in slabs is highly prone to mold due to condensation.
Know that slab foundation systems can have the same water condensation/seepage/drainage/water accumulation problems that all foundation systems can have, including basements. Building owners just can see the water damage easily. So people mistakenly think there isn't a problem, just because they can 't see it.
The difference in an unfinished basement, is that you can go down there and see or smell any possible moisture issues. You can also check plumbing pipes and connections to toilets above, from below. And in a basement it's easy to fix challenges or leaks when they do occur, hopefully in a timely way. Timely action in response to water damage incidents is the key to avoiding costly clean-up in addition to repair costs, and is key to avoiding health issues from long term water accumulation.
With slab foundations, the same leaks, water infiltration, even condensation can be occurring but you can't see the accumulation or check for it easily. Leaks and accumulation of water often goes unnoticed for a very long time as the problem grows unseen. Fixing water accumulation below slab foundations is very difficult and therefore very expensive too, as it often involves cutting up and removing pieces of concrete slab.
It seems some doctors and other health advocates have perpetuated the myth that slab foundations are mold resistant. As an architect myself, who has dealt with complicated health issues, I know lots about health remedies but I'm not the one to answer questions about how various systems in the body work. I do not recommend getting information on building systems and how they work best, from a medical doctor.
Attached is a picture of 'rising damp' in a solid masonry wall. There is no basement or crawl space, only a 'slab' foundation. Note that there are no gutters to carry water away. The very large roof of this building is dumping gallons of water against the foundation, where it is wicking up into the wall. I had a mold reaction myself while visiting this building (a church) recently...
The second picture is a university classroom building. Look around and you will see this often, especially after a rain event. Over time, the damage is evident even without the rain.