How soundproof is roxul / acoustical putty?

Question

I want to put Roxul and acoustical putty in the interior walls of the home my wife and I are renovating. She is worried that she won't be able to hear the kids (ages 5, 3, 0) in the next bedroom over if we do that. The home is 950 sq. ft. and has three bedrooms, all next to each other.

If I just put Roxul and use accoustical putty between the bedrooms (2x4 studs), how soundproof is it going to be? I understand that to get real good soundproofing, you have to use green glue, multiple layers of drywall, acoustical drywall, and RSI clips. I figured the Roxul and putty would just give us all a little bit of privacy without totally sealing off sound from one bedroom to the next.

Answer 1

It's impossible to say how soundproof an installation will be. We can make a reasonable estimate if we know all the details, including potential flanking paths. A wall of this type may give you an STC 45 or something (wild guess). But even if it were STC 300, you'll still hear a screaming child due to flanking paths. Just how much do you need to hear? You're not going to hear them plotting their first great escape, but if a child is in trouble, you'll hear about it, unless the stereo or TV is up fairly loud.