Critique my ceiling plan...continued

[JRSGodfrey]

Knightfly,

I would like to go with the reccomendation for the ceiling you gave in the previous thread. That is, having some acoustic treatment below two layers of sheetrock on resilient channel that is mounted on cleats half way up in between the joists.

I was in the space today and the question came up what to do about the junction of this type of ceiling with the walls. Since there is no hard cap beneath the joists, how to seal this intersection?

Should I try to frame the side walls up into the joists up to the subfloor? The joists in my space run paralell to the front and back wall.

Stumped.

Jay

[knightfly]

Jay, I hope you weren't planning on building this tonight, I'll have to give it a little conscious thought (I hate when that happens :=)

That's the cool thing about problems - solve one, and two more jump up to take its place... Steve

[knightfly]

Jay, I need a little clarification on your present situation - am I right that when seated at the mix desk, the ceiling joists run from your left to right and not front to back?

Also, this would mean that you need to interface the left and right walls with joists that cross them every foot, and the front wall (behind the mix desk, in front of the room) is parallel with the joists? If so, how far away from the front wall is the first joist?

Next, you said the rest of the ceiling was concrete, so we only need to interface 3 of the walls, correct?

Also, I saw a concrete wall with RC and wallboard, is that true of ALL the walls that need to be interfaced with the ceiling?

If you could post either a rough drawing in Paint or possibly a digital pic, it would go a long way toward speeding things up... Steve

[JRSGodfrey]

Steve,

Yes, the joists go left/right when facing front or rear at mix position.

In measuring more carefully (that is, not by eye) the joist are 3x8s on 16" centers. So I need to interface the side walls with joists that cross every 16" spanning approx 6'.

The front wall (speaker/console end) as planned will consist of a wall faced away from the studio framed up to the subfloor against the far side of the last joist with another wall faced to the studio framed to the bottom of the same joist. I've attached a (very) crude picture to show all of this (on a Mac -- can't use the drwaing prog you all are).

Height to bottom of joists is exactly 84.5"

The concrete ceiling starts about halfway back. So yes, only three walls need to be intersected -- two block walls w/ isolated stud walls of 2x4. RC, 5/8" x2, and one free standing 2x4 stud, RC, 5/8" x2.

I hope this is not getting too involved for a forum exchange.

Thanks in advance!

Jay

[JRSGodfrey]

Here's the pic. Somehow lost it on the previous.

[knightfly]

OK, now what's on the other side of the walls that need to extend up into the joists cavities? Do you need a lot of isolation there also? Because I'm still trying to figure out how to handle that part. It would be LOTS easier if you could spare about 2" of ceiling height, not to mention more isolation between upstairs and down.

The other thing is that this reduces the depth you have available by 2", which will ALSO reduce the effectiveness of my first idea.

Let me know what you think - if you can give up another 2 inches, it will be much simpler and quieter too... Steve

[JRSGodfrey]

Ok,

It is important to isolate around the perimeter -- on one side is more living space for us, and the other side my neighbor's.

The more I look around at the intersection of the joists and the masonry wall, I think I might have to abandon the ceiling treatment you worked out.
It might be a real weak spot -- even if I could seal the openings up there, there are quite a few conduits passing through.

One last idea I had to salvage this: Could I bolt or screw 2x8 material between the joists to cap the space at the ends, about 6" inside the room? (Would this help to stiffen the structure to support the weight of all that sheetrock?) I would then frame the side walls up flush behind these 2x8 "caps." I'll try drawing another diagram of this tonight.

Another idea: to preserve the most headroom possible, could I still hang a double sheetrock ceiling from single-legged RC attached to cleats on the sides of the joists so that the first layer of rock would just barely clear the joist bottom? I know I'll only be gaining a 1/2" or so, but since I will now have to treat the celiling over the console w/ rigid fiberglass, every bit will help. Would this scheme perhaps create a "springier" ceiling than double legged RC on the bottom of the joists, one that might absorb some sound energy?

Once again, long questions... Thanks.

Jay

[knightfly]

Fastening solid wood of any kind between the joists will allow serious flanking noise through - no matter WHAT part of the construction, you need TWO mass layers separated by as much AIR space as you can get, and physically ISOLATED from each other as much as possible.

Using single-legged RC is the only way to go, IMO - the double legged "HAT" channel requires separate, expensive, isolators or it doesn't do ANYTHING.

And yes, you could gain almost 1/2" by putting cleats up in the joist cavities so that the part of the RC that fastens to the sheet rock is barely below the joist bottom.

PLEASE READ MY ANNOUNCEMENT AT TOP OF THE FORUM... Steve

[JRSGodfrey]

Steve,

Thanks for the info. I will revise my plan. Also for the link. I'll be reading it on the train home tonight.

Cheers,

Jay