In addition to what was already said, there definitely is and has been many moisture issues on walls and exteriors in new construction. A condo building near me had to have its exterior completely torn off, and lots of sheathing, insulation, cladding, etc replaced due to a botched install of EIFS. Google for “EIFS failures.” This was a big problem in the 80s/90s or so but apparently it’s still happening, at least with subpar builders.

Because they use a dual layer construction with an air gap between the inner an outer walls. This gives space for condensation to occur and evaporate again without effecting the living space.

In old buildings with solid walls you can get condensation on the walls that will evaporate because the living space is heated and we'll ventilated. If you clad that wall in insulation you can prevent the evaporation which leads to damp problems.

> Interesting, why isn't the moisture on walls behind insulation ever an issue on new construction?

Newer building codes have started to mandate more external insulation:

* https://www.buildingscience.com/documents/insights/bsi-001-t...

Depending on the climate zone, up to half the insulation may be mandated to be on the outside (behind some kind of cladding (brick, stucco, siding) to protect it from UV and bulk water).

Per the above article, by having the outside be insulation, your interior structure is kept warmer, and so condensation is less likely to occur.

Do a search for "Joseph Lstiburek" and "Matt Risinger", who have lots of articles and videos on building science.

* https://en.wikipedia.org/wiki/Building_science

Old constructions are diffusion open, meaning moisture can move freely in and out of it. New constructions are diffusion closed, meaning you have a steam barrier on the inside which blocks the moist indoors air from traveling into the walls. This however requires an airtight house and mechanical ventilation.