E: From more reading, it looks like some kind of mineral wool will be the best thing to place between the studs. I also feel content adding MLV to the bathroom-side since the waterproofing underlayment for the shower is also effectively a moisture barrier. That way, any moisture-allowing failures can still permeate out the exterior wall and to the adjoining rooms.
As the title suggests, I want to soundproof my bathroom. It is right next to the kitchen (top hangout space) AND my disabled (relevant bc this is the only accessible bedroom) uncle's bedroom. We want to hang out and be able to use the bathroom later than my uncle wants to stay up, but the noise is bothersome to him. There are demons in his colon, too, which do not complement breakfast.
We live in this huge, cheap, almost-down-to-the-studs house that I bought so the only practical limit to renovations is money. How can I soundproof the bathroom? Right now it's just old lathe between his room and the bathroom, and the bathroom and the kitchen. I'm already planning to put 5/8" thick drywall once we get there, but figuring out what else I can do. We putty'd the back of the outlets in the shared walls, and made sure the doors are real tight so there won't be a fit issue there.
Brain Genius or Setting Myself Up for Catastrophic Mold with MLV?
I was thinking to put mass-loaded vinyl on both sides of the walls, but since the bathroom obviously generates a lot of steam and moisture, I am worried that small failures will trap a lot of moisture in the internal walls and lead to mold and structural damage. Now neither of the walls to the bathroom are structural but I am so afraid of mold damage. When I rebuild the shower, I plan to make it curbless and waterproof the shit out of its enclosure, but I imagine there will still be some amount of moisture leakage outwards especially since I probably won't do tile to the ceiling.
Which Leads me to a Brain-Genius Solution
Why not load the area between the studs with a lot of drywall? I can further isolate my uncle's room with hangers or other gaps so there isn't a rigid member (the studs) directly behind the drywall. Now space in the bathroom-facing wall in the kitchen is very precious. Losing 1-2" inches to isolate it would mean I can't use off-the-shelf cabinets and makes building it nice sort of impossible for what I can afford. I am categorizing the worst bathroom noises to be "aerial" noises and not structural noises since footsteps do not bother us too much. I wonder if I can contain them well by mass-loading the walls with extra dry-wall offcuts and things. It will be very easy to reinforce the joists this walls rest on from the basement so I don't see any drawbacks but I don't know how super effective this strategy would be.
Any advice is good! Like I said, my main concern is the effectiveness of bootleg mass-loading and avoiding a moisture trap. Also if it is relevant the building is brick with 2x4 studs on the external walls faced by plaster (in the old sections) and drywall in the new sections. Uncle's bedroom, the bathroom, and the kitchen are all along the same external wall. The plumbing wall for the kitchen and the bathroom is the same one.
Thanks!