I live in a second floor condo with a neighboring unit underneath. Their dryer was vented through the roof...I could visibly see the vent from my upstairs window. Last year the entire building had a new roof installed and the vent is now gone (roofed over). Would this cause moisture in my upstairs unit? I am definitely having some moisture problems, mildew smell, etc.
Not sure about the code, but doesn’t sound acceptable by any means. I think there are some dryer “vents” systems that vent into some reservoir that you will empty but I doubt local/building codes will permit it and I don’t think it is permitted for gas dryers.
Bottom line - I think you need to vent outside somehow - hammer drilling and 6”-8” hole in a wall is not a fun day imo. Roofers shouldn’t have closed a vent - what were they thinking.
It's unlikely that you'll experience moisture buildup in your living space if the vent is in the attic, and not in a wall or other interior cavity. The humidity in the attic could cause mold and eventually rot, but the ceiling materials and insulation (if present) should adequately prevent significant moisture transfer to your rooms.