I live in an apartment building that has 24 units which all the bathrooms vent into the hollow walls or their neighbors bathrooms upstairs. (so in their ceiling, the smell and moisture comes out through my floor). All the units vent to the interior. There are four dryers in the building which also vent to the interior. Nothing vents to outside. It has been this way for at least the past five years. You can remove parts of ceilings and see the mold on the backside of the sheetrock or sticking to the framing. You can also see the mold in all the corners of rooms down by the floor. It looks like a really fuzzy black caterpillar coming out of the corners.