"If I understand this correctly, then, the neoprene rubber on TOP of the new cap should NOT touch the existing ceiling runners?" -
The new wall frame cap should be TRAPPED BETWEEN two runners as I've drawn, padded with neoprene - what I'm calling runners are the flat 2x4's you've nailed across the bottoms of the ceiling joists, which are the "on edge" framing members that your subfloor is nailed to the tops of. The cap of the new wall frame should NOT be UNDER these runners, but sandwiched BETWEEN them with the neoprene keeping it from hard contact with ANYTHING.
" i.e. leave 1/8" gap and don't worry about caulking the rest of the gaps along the length of the cap? " -
That's right. The only place SEALING is important is corners/seams where drywall meets drywall. Everything else only exists to hold up the drywall. (Kind of like everybody else in the band is only there to make Kenny G sound good...)
Ok. So, now that I've got this figured out, back to my original question:
In what order should I put this construction together? My thinking is this:
***Build the runners/cap(with neoprene) using clamps as suggested, THEN mount the entire thing to the existing ceiling, propping it up with 2x4 studs (or similar) just so I can get it screwed to the existing runners (screwing in just the two surrounding runners and NOT the cap?).
***Build the new wall TO that new runner/cap (and on top of the floated floor). " -
"***Put up drywall on wall, then ceiling, wall, then ceiling, with caulk after each successive layer. " -
"Does this make sense? (sorry, I'm a novice as you can tell). " -
Doing it that way would be possible, but pretty tricky to get right. Also, alternating layers is good for wall to wall intersections, but the object in this case is to suspend the ceiling leaf (all layers of it) inside the wall leaf (all layers of it) so that the RC can maintain the flexible hanger function and allow the ceiling to float (semi)free of the walls (but still SEALED to them with caulk) - BTW, this is one area where you DEFINITELY need to find REAL acoustic-rated caulk - these joints MUST stay flexible and SEALED, or your isolation is history. Look closer at the drawing - I drew it EXACTLY as it should be built. (Other than putting the RC on the OTHER, HARD contact wall frame)
I'm going to assume (your pix don't show for sure) that the floor area in your iso booth is SMALLER than the area of your (to be added) second wall - if not, you could build the entire wall frame on the floor, then stand it up and fasten it in place.
With less space to work with, it gets more fun
What you will need to do is measure very carefully so you know exactly what TOTAL height your frame needs to be, allowing 1/2" for the neoprene across the top and the 1/8" gap between the top of the top pieces of neoprene and the existing joists - note that the neoprene top spacer will be under every other joist (if your joists are on 16" centers, you can go every third one) Your side pieces of neoprene will also be directly under a joist - all three pieces of neoprene should line up under a joist. It doesn't matter WHICH side of the TOP piece of neoprene you glue - since it won't be a tight fit, either the top can be glued to the joist or the bottom can be glued to the cap of your wall frame. It would probably be easier to glue to the underside of the joist, and keep that piece shorter than the width of the frame cap. That way it won't interfere with placement of the SIDE pieces of neoprene, which ARE fairly critical.
Once you are SURE what all the measurements need to be for your wall frame (be sure to include top and bottom plates/caps in the total height PLUS the neoprene and air space, subtracting those from the total height between floor and ceiling joist to get actual stud length - if your floor or ceiling joists aren't even, you'll need to adjust overall dimensions so that NONE of the ceiling joists contact the top plate.) -
Anyway, once you're sure of dimensions, you can cut all the framing pieces and mark any that are unique so you know where they go - Also mark one side of each stud's location on the plate and cap, with an X next to that mark - this shows which side of the mark the stud goes on, and the LINE is the edge of the stud. Like this lX (pretend this line of text is the cap or plate)
Now, temporarily fasten a 2x4 horizontally across all the studs in your existing wall frame - fasten this LEVEL, and about 6-7 inches above the floor, on the side of the existing frame that will be toward the NEW wall frame. This temporary 2x4 mounts to the existing frame on edge - then, fasten a second TEMPORARY 2x4 laid flat on top of this one, to make a 3-1/2" wide shelf near the bottom of the existing wall.
Use one stud as a measuring tool, put one end of it up against your new TEMPORARY "shelf" , and the other end goes up diagonally across the room to the OPPOSITE side wall - if that wall is still only framed (no panels yet) put ANOTHER temporary 2x4 LEVEL across the studs so that each stud you lay across this "bridge" will stay aligned with the REST of the studs til you've finished nailing your new wall frame together. You will be assembling your wall frame in mid-air, so you can get at both the bottom of the bottom plate to nail through into the studs, and also get to the TOP of the TOP plate, so you can do the top end of the frame after the studs are nailed to the bottom plate.
All this seems like a pain, but it will work - otherwise, you'll need to learn how to "toenail" without letting the framing member slip around sideways, and that's not always easy even for a pro.
Next, you'll put your studs on the bottom plate (the one resting on your low shelf) one at a time (starting with the one furthest from the door) and nail them with two 16d nails through the bottom plate and into the stud, making sure you're not too close to the edge of either the plate or the stud. 1/2" is enough, provided you aim your nails so they get progressively FURTHER from the edges of the wood as they go in.
Once all studs are nailed at the bottom plate, you can put a temporary 2x4 across the UNDERSIDE of the studs, near the tops, and parallel to the bottom plate - this will keep all the studs from trying to sag individually til you get the top plate nailed on.
Before you start your wall, you can put up the runner closest to the existing wall, and glue pieces of neoprene to it coincident with the chosen joist locations, so you can eventually tip up your wall frame until it hits the neoprene stops. If your existing runners are too close to where the new wall goes, there won't be room enough to tip up the wall frame without hitting them - you may have to slide the bottom of the wall frame AWAY from the existing wall far enough to allow the top to get past the runner if that's the case.
Once you have the frame built, you can lift it off the "shelf" and set it on the floor, with the far (upper) end resting against the far wall. Remove the temporary shelf and tip up the wall frame. You can hold the frame up against the neoprene stops with a couple of C clamps til you get the bottom plate positioned so that the studs are plumb (like level, only vertical) -
After the wall is trued, you can fasten the bottom plate to your floated floor, making sure you don't use fasteners that are long enough to "short out" your floated floor - then you can glue one side of your inside neoprene pad to the top plate (in line with the other two) - then, place the new runner up against the neoprene pads (all of them) clamp them tight enough to squeeze the neoprene noticeably, and fasten the runner in place, (finally) trapping the top plate of the new wall between two padded runners.
Have a beer - I'm thirsty just THINKING about this...
"One more question for you:
Wondering if a single layer of soundboard screwed to the joists and between the runners would help isolation on ceiling (cut in 9.5" wide strips to fit between the runners to cover the insulation, then caulked to fill the gaps). It's half inch soundboard, so there would be a gap between it and the RC1 which would then get mounted HOW??--ALONG the runners or ACROSS the runners? [See picture#1 for reference]" -
This would be a BAD idea. Re-read my comments on the last drawing about ONLY two MASSES between any two areas to be isolated from each other.
I'm ready for a break - if this doesn't make sense to you, let me know and I'll draw another diagram... Steve
