It is necessary to understand how modern building materials perform relative to older building materials for some of this to have impact. Old building materials (old growth lumber, lime mortar, common brick) can absorb a certain amount of moisture and still perform adequately. Old growth lumber is full of toxic saps and resins that inhibit decay and rot. Lime mortar and common brick “breath” absorbed moisture back into the atmosphere when conditions change. It’s the reason old structures have withstood time so well.
Modern building materials are largely tree farm lumber (grown at highly accelerated growth rates) with the result being punky/soft wood that absorbs water and rots quickly, various panels and sheet goods that are made of sawdust, wood fibers, and glue, plastic foams and wraps, waterproof paints and finishes, and materials that, in general, tend to absorb moisture and retain it, and that are not designed to withstand any amount of water.
The result is buildings that are improperly constructed (lacking correct waterproofing details) with modern materials tend to retain water caused by leaks, the “plastic” materials and wraps all tend to inhibit evaporation, with the result being the retained moisture causing mold growth, rot, and structural damage.
If buildings are built “wrong”, the result isn’t just staining and nuisance; the moisture can cause building failure. We are now starting to see the a growing number of these failures on houses that were built improperly during the boom period of 1996-2006.
If I haven’t made it clear by the preceding explanations, let me state it simply. This is serious business, not just pickiness about details that weren’t finished properly. These are the underlying causes of the growing problems with mold, rot, and sick building syndrome in new construction.