What causes this?

[n74tg]

While out driving around today I saw several houses in a subdivision that all had this problem.



This is a synthetic stucco siding; some call it EIFS I think.  On one house it looked a little
like mold growing in between the studs on the outside surface.

Anybody seen this before?

[MountainDon]

Never on a wall.


I see effects similar on roofs here on frosty cold mornings. The roof will have a frost all over. Those with less well insulated ceilings will have the frost melting off between the rafters.

I wonder if it's related to some similar heat transfer or conduction thing? 

[jb52761]

Think Don nailed it...It would be interesting if you were to drive by on a few other occasions, at different times and during different weather conditions, and see if things have changed...

[JRR]

Unfortunately, here in the hot southeast, I see it a number of times in subdivisions that are just a few years old.  Like already suggested, I've always attributed it to poorly assembled walls .... skimpy insulation, missing drain/vent planes, inadequate vapor retardents, etc.  I'm convinced if the walls were opened and inspected ... a triving mold culture would be found.