There Are Dark Mold On My Window Sill, Is That Bad Condensation Problem In House?

Condensation problem in house? - there are dark mold on my window sill, is that bad

my friend just renovated a separate annex Tennant. everything went well for 3 months before transferring to the company after 1 month, if the flat wet with condensation that form increasingly seagrass rug from under the bed, behind the couch and everything was always the air. not all the windows during his time, has a small bathroom a fume hood. I went in and could not believe the amount of water (pools) in each of the window (he SECONDARY double glazing) on the ground, but the worst of all is the sea of grass is like a thick layer of fine white fur around under the bed under the sofa, etc., is very dark, after the vacuum cleaner and is very moist. My friend is devastated because he can not afford to lose TennaNT can be as kind, goes without Tennent? I began by selecting all the windows and the command of a fume hood for swimming. This hot greenhouse effect on the tubular wall under the bed, etc.