Hi, Angie, well, I've been in the construction business for well over 35 years, but have never ever heard of this problem with mold.? but to put your mind at rest, you can replace the foam with rockwool of fibreglass product, The Styrofoam is a very good insulation for the heat/cold but not so good for sound, Rockwool ( minerail fibre) is good for both also Fibreglass, ( not the best material to work with, from the fixers point of view,.) Styrofoam is a petrol by product but does not burn but gives of a black smoke, which can give you problems, and it melts like hot tar. People put this on kitchens ceilings, looks very nice and all that, but if/when theres a fire it can burn ( not in the sence of flames every where) but droplets of hot plastic drop down ( and if you get some on your arm.. boy, you know about it.
I myself would go for the mineral wool ( Rockwool) but have a chat with the builder, he/she will know about it than you and can advice you good luck.. John 2000