What problems would there be if the pipes were touching the backside of the first layer of rock?
IF the pipes went nowhere else (not to other areas needing to be isolated) the low end isolation wouldn't change with hard contact - this is almost entirely a function of the air gap between leaves. However, the midrange would suffer by about 12 dB in this case by NOT having resilient mounts.
Then there is the water noise and flanking problems; these DEMAND that you NOT let the pipes touch the back of the first layer of gypsum. If you can, post a sketch of what you intended for a method of dropping the ceiling at the pipe area, and I'll let you know whether it'll work.
Your earlier questions -
Insulation – As far as the amount of insulation in the cavities - from my findings here there should be enough so it is lightly compressed but not so stuffed to make it couple the other side. Should the insulation be flush with the studs, can it extend beyond the studs and if so by how much? I used R38 for the 2x10 (ceiling) and R19 for the 2x6 walls.
For 2x6 walls, up to about 1" of compression is fine for standard fiberglass building insulation; NOT for any of the higher compressed stuff such as rockwool, semi-rigid fiberglass, etc.
Also how important is that when handling / applying the insulation that you don’t compress it, bend it e.g. be “gentle” so to speak? The reason I ask is I had a friend help installing and he was whipping the stuff around like a rag doll. Weird question I know, but he was like “don’t worry about it, it’ll be fine”
Doing that will release more fibers into the air and make it even more necessary to wear masks and vacuum more often, but won't hurt the insulation in any measurable way (unless he's so vicious he destroys the batts
:?
Screws – I think I purchased 1in for the first layer and 1 5/8in for second layer (both fine threads). Is this correct? I used the coarse threads for hanging the channels and rock in other rooms etc, but thought the fine thread would be better for screwing the rock to the channels?
Coarse threads are for attaching to wood, fine threads for attaching to either light steel studs OR Resilient Channel. Going into wood, you want at least twice as long screws as the gypsum you're fastening. Into steel, it's useless to have more than enough screw length to engage all the steel thickness with screw threads so 1/2" extra is fine. Just make sure you don't put any screws into RC where a framing member is behind the RC, or you'll hurt isolation a LOT.
Caulking - I only have one adjoining or shared wall that has rock on the other side of my room (the others are exterior walls and the ceiling). I forgot to caulk the rock seams (from the backside) and where the rock meets the studs. Should I take everything off and do this?
NOt necessary; all you need is a hermetic seal SOMEWHERE between the two areas. See this thread for some detail -
http://www.johnlsayers.com/phpBB2/viewt ... 3&start=15
Rock orientation - is it necessary when putting on the second layer of rock to orientate the seam opposite from the first layer e.g. first layer seam goes horizontal the second layer seam goes vertical? I plan on leaving .125in gap at all of the joints and caulking the seams with acoustic sealant.
Walls - for 2-layer walls, first layer goes vertical. Second layer goes horizontal. Placing first layer vertical improves strength, placing second layer horizontal improves looks (easier to get smoother, flatter surface) - between sheets seams can be mudded and taped instead of caulk. Perimeter should be done per the above link.
Orientation of RC’s – does it matter if some of the channels switch “orientation” on a given wall, see pic? Also, some of the channels seem to be close to the stud (the short leg). When the rock goes on will it be pulled away, sort of center itself? Should I give some of the channels a tug
RC should be installed on walls with the short leg DOWN and fastened to studs. Only exception to this is if you don't have room to fasten the BOTTOM RC, it can be done upside down. Leave about 1" gap from end of RC to adjoining wall, no need for fasteners between rock and RC closer than 2-3" from adjoining wall. Do a "Z" joint at corners, finish with flexible plastic inside corner, light mud/tape.
http://www.johnlsayers.com/phpBB2/viewtopic.php?p=20003
Door - I purchased a solid (wood) core interior door (haven’t installed anything). I’m thinking of exchanging it for an exterior metal solid core foam door instead?
Interior doors are typically 1-3/8" inch thick; with perfect seals, about STC 29. Exterior doors are 1-3/4" thick, solid wood would be about STC 30. IF the metal door you're looking at has better specs, fine; but you'd get more by using TWO doors separated by a couple feet of air space (vestibule) if you have the space. Even separate wall frames and separate doors separated by a few inches will beat ANY single door costing less than $5k. - SEALS are the weak point.
It looks like for the closet, I will only put up one layer of rock because of space. Bad planning on my part. Still undecided though.
?? - Did I miss a floor plan?
For the oak trim (baseboards and casements around windows and doors) should these be attached to the channels as well? I was thinking of installing short scraps of channels to the window + door framing for the trim to attach to?
They can attach to the channels or to solid structure, but not BOTH. Heavy-based moldings could conceivably attach thru their base to solid structure (floor) leaving a small air space for zero hard contact, but it's usually easier to attach to the floated wall (leaving a small gap to the floor or ceiling)
HTH... Steve