We are tearing out lots of mold in a house in which two bathrooms were installed by incompetent amateurs. And the more we tear things down, the more mold we find.
What I would like to know is; is their any way to keep studs and beams covered with mold in place? There are lots of chemicals that supposedly kill mold, but most of them only kill the surface, not the hypha which have grown into the surface. In other words, they would only work really well on concrete, stone, etc.
Also, are there any natural products which can effectively deep kill mold? Or am I stuck using some sort of toxic chemical? (Or should I just tear everything out?)
Bleach is by far the best mold killer. It works a lot better than hydrogen peroxide and it's a lot less expensive. Repeated application to wood so that it soaks in will kill hyphae that are burrowing into the structure of the wood.
And after bleach has done its work and decomposed, it doesn't leave a toxic residue. Bleach is sodium hypochlorite, NaClO, and its killing power comes from the powerful oxidizing effect of the ClO- ion. Once it is done oxidizing something and the oxygen is gone, all you are left with is NaCl -- regular salt.
The trick with using it is to protect yourself so that none of that powerful oxidizing effect takes place on your skin, eyes, nasal passages, etc. Most commercially sold bleach preparations are around 5%, which is more concentrated than necessary to kill fungi. If you dilute it up, 1 part in 10 parts of water, it will still be efficacious and much easier to work with. Most of the bad reputation bleach has as a chemical to be avoided is because people use it carelessly at concentrations larger than are necessary.
If you give your studs and beams a thorough bleach treatment and then, as Michael says, keep it properly dry, your problems should be solved.