Bonus/"attic" spaces and soundproofing questions
Brushing up a little on soundproofing concepts. I haven't had to deal with a space under the roofline before, read all the threads and articles on the subject I could find but had a few questions that weren't completely clear for me.
Most concepts are the same, DD+GG, +/- clips and channels, for walls and ceilings.
What is the preferred framing approach for the sloped part of the wall/ceiling made up by roof rafters? Specifically, should the knee wall be attached to rafters with isolation clips? Flat part of ceiling the same? Or OK to be rigidly attached since this is roof and not adjacent to any other room?
Or should I entertain the idea of a floating double rafter system akin to a double stud wall, where a non-structural set of rafters is nested between the actual structural rafters, and supported by the knee walls? These would probably have to extend to the floor, at least in some locations, even if the flat portion of the ceiling joists serves as collar ties, just to keep structurally stable. I suppose where this happens they might could ride on a footer that sits on a rubber mat to help with isolation. Has anything like that been done?
Or, a short segment of floating rafters that are suspended from the structural rafters by a relatively few isolation points?
I'm honestly not sure what effect this double rafter would have on insulating the space between rafters to satisfy code. I plan to have the structural rafters sized, if possible (I think they can be), to span the required horizontal distance without a structural knee wall or purlins (won't have load bearing wall aligned underneath). So there wouldn't be anything in the way I think of a second set of rafters. This would add load to the structural rafters though, so not sure how that effects sizing to code either.
Floor will largely be ceiling of 2 story high family room and entrance. Much of the span unsupported, I think 16" structural I flooring system will be adequate, but may investigate a few steel beams to reduce bounce. I can probably do hat/clip and DD+GG for the undersurface ceiling, and rubber mat floating floor in the theater room. Not sure I can do any better there.
Just in general, seems these roof rafters are going to short circuit a lot of effort to isolate framing. Best to just accept it, rigidly attach framing, and rely on clips and GG for isolation?