Wall Decision -- wood or metal studs?

[JRSGodfrey]

I'm getting very close to building out my space. Layout can be seen here: http://www.johnlsayers.com/phpBB2/viewtopic.php?t=966

Three of the perimeter walls are thick masonry block plus face brick, rendered. The fourth (the front, behind the speaker wall) is a standard sheetrock wall that I am going to beef up with another layer of sheetrock and insulation. The inside dimensions are 9' by 13' w/ a 7' ceiling.

My wall plan up til now has been 2x4 studs on 16" centers spaced about 1" from the perimeter masonry wall and 6" from the existing standalone sheetrock wall. Rockwool or equivalent in the the cavity. Over this resilient channel and then two layers of 5/8" sheet rock. This structure will be approx 6" thick.

After reading here and there about walls, given the massive structure in place, it seems I could get similar performance w/ two layers of sheetrock over steel studs w/o RC -- both layers driven into the studs. I am not experienced at constructing walls, so this option, without the RC and laminating layer, appeals to me.

Since I have the masonry walls (leakage to the existing sheetrock wall side is less important -- storage area adjacent) to hem in the bass, can I get as good isolation from the steel studs? And will the more flexible walls give me a little better sounding room?

The ceiling, btw, will be sheetrock over RC for maximum isolation.

Thanks!

Jay

[knightfly]

Hoping you've already read this, if not it's time -

http://johnlsayers.com/phpBB2/viewtopic.php?t=598

Not sure it's mentioned in that thread, but 24" centers improves wall performance by about 2 dB. Lightweight (25 gauge) steel studs need no RC, structural (20 ga.) DO need RC. One side only, of course.

With heavy masonry, you can use a single 1/2" wallboard and improve bass trapping in the room somewhat while only losing maybe 1-2 dB of isolation. The depth of air space between masonry and inner panel is part of the panel calcs. Only formulas I have for this are based on 24" centers.

More later, gonna be late for work... Steve

[JRSGodfrey]

Thanks Knightlfy -- Read that post over again.

So, you are saying I can go with the steel studs? They will be non-structual in my case. I will change my plan to 24" centers.

With one layer of 1/2" over the studs, perhaps I can increase the airgap. I guess I can always build it w/ one layer and see how it isolates, and put another layer of 5/8" on top if I want more. Good idea?

Also, I plan on building the ceiling first, and then bringing the walls up to it. Is that the proper order?

One more Q: where the wall frame meets the bottom of the joists, I know I should I intall some sort of isolator. Wall felt or rubber, or other?

Thanks again.

Jay

[Aaronw]

Check out the thread I have posted. About halfway through, we start getting into some wall construction and ceiling construction. There are also some diagrams that may be of some help.

http://www.johnlsayers.com/phpBB2/viewtopic.php?t=839

Aaron

[knightfly]

Jay - The steel 25 ga. studs will be fine for non-load bearing walls - You'll want to seal your outer perimeter before building the inner shell.

For low ceilings, I prefer to build walls first - The rest of this post will be based on that assumption. On OUTER wall leaves that are perpendicular to ceiling joists, you need to install blocking between joists if it's not already there - put a couple of layers of wallboard over these blocks for more mass. frame your steel studs up for inner walls -

if necessary, you can attach the OUTER side of the top channel of the steel stud frame directly to the ceiling joists by fastening a piece of 2x4 to a joist (or joist block) - hang this 2x4 down a few inches below the upper edge of the top horizontal wall frame channel, then you can screw the OUTER flange of the top channel directly to this "dangling" 2x4. This will stabilize the wall in the middle, it should be done every 4 feet or so.

The reason this is OK is because of the inherent flexibility of the 25 ga. studs - they flex enough to decouple the inner wall leaf (mounted on the INNER flange of the wall studs) from the OUTER flange (screwed to the stabilizer 2x4 mentioned above.)

The BOTTOM horizontal channel should be bedded with 1 or 2 layers of pink "Sill Seal", available at Home Depot or Lowes, etc - this keeps things from vibrating. No caulking is necessary until you start putting up wallboard. Put your first layer of wallboard up resting on 1/4" spacers, screw it onto the framing, pull the spacers and caulk. Finish that layer, mud and tape, then repeat with all seams offset at least 12", 1 whole stud offset is better. Offset seams vertically as well, 24" is best. See the other threads for fastener info, marking to avoid collision, etc.

Run the wallboard up to the top of the horizontal channel, but NOT so far as to touch the joists. Neither should the horizontal channel touch these joists. The only contact in this area should be with the OUTER flange of the "C" shaped studs or the OUTER flange of the horizontal top channel. If necessary, use more "dangling 2x4's" to stabilize the top of the wall frame, just make sure NO part of the framing touches the wide top of the top channel, or the INNER flange of it. These need to be able to flex.

Once the wall is up and finished, it's time to apply any reinforcement of the UPPER leaf of your ceiling, the one that's part of the subfloor above. Depending on your need for isolation, putting a couple of layers of sheet rock up against the subfloor will improve the mass in that leaf quite a bit.

After any reinforcement, insulation is next - for this, standard building insulation is nearly as good as the rigid if you FILL the cavities - it's actually BETTER if you allow the raw fiberglas or paper covering to touch the inner ceiling panels, because the damping helps reduce low frequency Transmission Loss.

Next, decide how many layers of wallboard are going to go on the ceiling - if 1 or 2, put the RC perpendicular to joists and on 24" centers, leaving 1" clearance between the ends of the RC and your walls. The RC should drop down to a level that's about 1/4" to 1/2" below the top of your wall paneling. If you're going to use 3 layers on the ceiling, you'll need to put the RC on 20" centers - RC is a spring, and springs are NOT springs unless they are in the center range of their travel - more weight will extend the RC "spring" more, lessening the isolation effect. Putting the RC closer together allows the "spring" to be closer to the center of its travel.

Put temporary spacers around the wall at ceiling panel height, so that your ceiling panels stay 1/4" away from the walls. Caulk each layer after pulling the spacers. Offset all joints for successive layers, same as wall construction.

On RC or 25 ga. steel studs, each layer can be screwed straight through using longer screws for subsequent layers.

CEILING FIRST, WALLS AFTER -

For this method, you WILL need some kind of isolation layer between top of walls and ceiling - you also need to keep the ceiling from reaching to the outer wall leaf. I don't prefer this method, partly because it makes it hard to stabilize walls and still maintain isolation.

I've got an idea for a DIY wall brace that will provide flexible mounting for steel stud walls with better isolation than the method I outlined above, but it will take a drawing or two. I'll post it here when I get it finished.

Yes, you can always add layers to either wall or ceiling - just leave 1/4" gap where one meets the other, and caulk when done... Steve

[JRSGodfrey]

Kngihtfly --

Couldn't of asked for a more comprehensive reply. Thank you.

I now feel ready to do this, despite my lack of building experience.

I'll report my progress -- and no doubt more questions.

Thanks again, and Aaronw for the pictures to make it clearer.

[JRSGodfrey]

Knightfly, you wrote:

"On OUTER wall leaves that are perpendicular to ceiling joists, you need to install blocking between joists if it's not already there - put a couple of layers of wallboard over these blocks for more mass."

I looked at this area between the joists and there are several voids where electrical conduit is passed through, as well as some piping that is no longer used and has been cut off. In some places the brick block is rather loose. I plan to fill as much as possible with cement.

So without a sturdy backing, what do I attach this sheetrock blocking to?

I came up with the idea of fastening 2x2s to the joists (perpendicular) flush to the block wall. I could then sandwich a couple layers of 1" 703 in between the 2x2s and then screw a couple of sheetrock panels to the 2x2s, compressing the 703 behind. I've got a lot of 2x and sheetrock scraps from the adjecent kitchen renovation I could use for this.

I hope that's clear.

What do you think?

Jay

[knightfly]

"So without a sturdy backing, what do I attach this sheetrock blocking to? " -

If you already have masonry there, just fix it with something like Fixall Concrete Repair - that will be your OUTER leaf.

"I came up with the idea of fastening 2x2s to the joists (perpendicular) flush to the block wall. I could then sandwich a couple layers of 1" 703 in between the 2x2s and then screw a couple of sheetrock panels to the 2x2s, compressing the 703 behind. I've got a lot of 2x and sheetrock scraps from the adjecent kitchen renovation I could use for this" -

Without a picture, I'm not positive but it sounds like you're headed for "triple leaf" country, and you don't want to do that. Remember - from ANY area to any OTHER area you're trying to isolate (whether one area is the outside world or not) - you want MASS, Air, MASS . No more, no less. Furring out from your concrete wall with insulation and sheet rock will make a Mass-Air-Mass construction - if you then put any more between the two areas, you will only WORSEN your isolation.

If you could post a drawing of what you intend, I could be sure... Steve

[JRSGodfrey]

Knightfly,

I've tried to translate your directions to paper. A couple of very crude drawings not at all to scale.

Does this look right?


Thanks.

Jay

[knightfly]

Jay, that looks exactly as I described it - another way, slightly better isolation - check out these drawings of a DIY sway brace, along with a detail of between-room wall/ceiling construction -

http://www.johnlsayers.com/phpBB2/viewt ... 8&start=45

Graveyard shifts be upon us again, so it may be a day or two before I can get to others' questions... Steve