If you live someplace that is dry enough (like say Arizona) then it is actually OK to vent the bathroom fan into the attic.QUOTE]
I live in Las Vegas and we have practically zip humidity year round. That said, mold is a HUGE issue in homes here. I briefly worked for a law firm, and I have seen horrific photos of mold growing in the walls and ceilings of homes in this arid part of the country.
People get really sick and don’t even know mold has been the cause.
Good for the lawyers, bad for the schmucks who didn’t think mold grews in low humidty areas.
If I ever build or remodel my own house, I want to insulate the bathroom walls just for that reason, particularly if it’s one of those powder rooms just off the living room or foyer. And when I visit friends, I usually try to use the upstairs bathrooms just for that reason. I had one friend who had a powder room adjacent to the kitchen with a louvered door. There was no way that I wanted to use that for anything that would make noises.
I can’t speak for other climates, but here in the midwest, venting to the attic is baaaaad and I think even against building code. Even a low number of roof vents can literally destroy a roof from moisture/condensation. I agree that 4 months shouldn’t make a big difference but remember, this is a new fan. If the old fan was indeed 30 years old, it may not have been venting that much anyway. So now you have a new fan that is actually working properly and you have much more moisture going into the attic space.
ETA: Insulation in interior walls is an amazing invention to me. My son used to host computer parties with 10+ 14-year-old boys and with the doors closed we could barely hear them in the next room.
I tried to move the vent to the roof but a government agent said it would kill of an endangered species of mold so I was forbidden to do it.
Seriously, 80 year old house, Vented bathroom fan into a poorly insulated attic and no mold. And I have side gable vents that should make it worse. I have the ultimate mold factory looking for clients.
I suspect it’s because there aren’t enough people using the bathroom to create the problem. Frankly, it’s really easy to add a roof vent although this isn’t the best time of year to do it.
If I were in your shoes I’d wait until spring, since another four months of venting to the attic seems minor compared to the trouble I could get into trying to cut a hole in the roof in the middle of winter. Knowing my luck, I’d install something wrong, and then be trying to fix a leaky roof during the winter…
there are insulation materials that claim to be optimized for sound deadening in interior walls if that is a purpose. i haven’t used or priced or compared to thermal insulation.