Existing wall is already MASS/Air/MASS so the new wall....?

What seems to have gotten lost in this discussion is what constitutes a "leaf." It has nothing to do with "seals." A leaf, plain and simple is a mass (as in mass-air-mass). It doesn't matter if it's one layer of drywall or two layers - unless you inadvertantly got a squirrel (sp?) between the sheets of drywall, you get a thicker (more massive) leaf with two layers, not two leaves. When you introduce an air gap (like the studs) between the two masses, you now have two leaves. The drawings that Kendale posted show this quite clearly. If you read Paul Woodlock's build diary, you will find that he discovered the third leaf effect in his own "bomb shelter" construction after he put up (and sealed) his two doors leading to the house. As I recall, he had turned up the boom box in the studio and then went into the house to see how well the doors sealed. There was a piece of plywood or MDF or something in the house which he picked up to take back into the studio and as he approached the closed door (which was silent), all of the sudden he could hear the music inside quite clearly. All he had was a flat piece of wood in his hands and that "third leaf" destroyed his isolation. It wasn't a "sealed" leaf. Just a piece of wood. As I was advised early on in my studio build, there <b>IS</b> a point where the air gap is so large that third leaf (or quad leaf in my case) is not an issue. But my air gap was a hallway between two free standing rooms and was over 8'. Unless you want to loose 8' or so around the entire structure (including the ceiling) you will either have to go the "bull and hammer" route OR sacrifice isolation. Since you mentioned that you are going to have drums and neighbors within 25', you would be better off to error on the side of caution, proven practice, and the advice of experts (like Rod, not me) and build it "right." len

I agree with Ro. From what Rod said above, option 1 creates a 3 leaf system. You are better off with option 2 overall, but Man, I can understand you NOT wanting to tear those existing walls out... :o QUESTION for all...(To clearify "Air Gap") When you refer to "Air Gap", is the distance from one LEAF to another considered an "AIR GAP AREA" even if it has insulation in it? (I'm talking about insulation with NO paper) (Seems I read something about a connection between an "Air Gap" and insulation on this site)

Yes, insulation counts as "air" in the Mass-Air-Mass equation, provided air can pass through it. Examples of insulation that does not count as mass are closed cell foam, kraft paper backed batts (common mistake!*), and insulation that is packed in so tightly that it forms a bridge between the leaves (ideally, you want slight pressure on both leaves to help dampen the leaves, but not so much that it becomes a path to transfer vibration from one to the other). *Actually, I think kraft paper backed batts are semi OK if the paper is against one of the leaves... --Keith :mrgreen:

Ok, guys. You've convinced me that I've got to bust out the sledge hammer (and remove the existing inner drywall). I was hoping not to have to destruct the current wall too much, but at least this way I will be able to beef up the outer leaf, and also get to the electrical easier. As for adding mass to the outer leaf ( closest to the neighboors ) this will be possible when I remove the existing inner drywall. But by doing that basically I will need to pull out the insulation, and then add drywall inbetween the studs, right? Does this layer need to be sealed from stud to stud? And what would be the best way to secure the new drywall layer....screws or glue? ( if screws, they would need to be short enough not to poke out into the oustide) This will be interesting...I plan on documenting this project very closely so hopefully others will learn from it. Thanks a bunch!

Good move. :-) I hope you don't discover that a layer of OSB isn't between your drywall and your studs... That's what I ran into on my south wall and the reason I am forced to deal with three leaves. (Here in California, certain walls must be reinforced with OSB for seismic stability.) You'll have a huge mess on your hands, but you'll be glad you did it once it's over. I took lots of photos of my teardown and beef-up in my thread, starting around page 24... Don't miss it!

If it were me I would glue it on the edges (not in the center areas unless it's "green glue" ) http://www.audioalloy.com/index.html (Green glue is not "glue" as thought of in the traditional way) You might want to consider Green Glue compared to extra sheets of drywall if losing space is a concern. From my understanding it can help with sound isolation to some degree. Also, if you beef up in between your studs or anywhere else, make sure your floor can take the additional weight. I have seen it recommended to screw "beefed up" drywall to ceiling subfloors, but I'm not really sure if that applies to "outside walls". I'm like you though...I don't want screws sticking out from the outside of my house or sticking into vinyl siding (if you have it). One of the more experienced people here can tell you for sure about this. Also, I would use acoustical caulk to seal each piece of "beefed up "drywall to the studs in each cavity. I would then use a "cleat" to hold the new beefed up drywall to the MDF or what ever was used as your "outside" wall. (once you take the insulation out). Give credit where it's due...This is construction I modified but originally borrowed from Sharward

Remember -- wider air gaps give you better isolation, especially for lower frequencies which are the most troublesome. I have heard that 12" is a good number in that you get a lot of benefit with relatively little lost square footage. Remember that the air gap is measured from the backs of the wall surfaces, not the studs... So you can achieve a 12" air gap using 2x4s that are 5 inches apart (3.5 + 5 +3.5 = 12).

bump for Knightfly.... thanx, K

UPDATE: Removing the drywall was not hard at all!! I even managed to remove it in 8'X16" sections that will fit perfectly inbetween the studs after I remove the insulation to beef up the outside leaf. The best method I found was to 1. find the studs with a studfinder, and mark them 2. with a large drill bit drill until you hit the stud, then angle and push towards the piece of drywall you are trying to remove until it slips off the edge of the stud. Do this in 3 or 4 spots vertically up to 8 ft. 3. using a long straight edge, connect the dots, and draw a line with a pencil. 4. Using a jig saw, start sawing from the bottom right hole up to the top right, and across to the left stud, using the header as a guide. 5. while keeping some pressure on the piece of drywall so that it does not cave in on you, do the same thing on the left with the saw. 6. cut from the bottom holes down to the floor using either the jig saw, or a drywall hand saw. 7. pull the section out, and lay it on the floor. CAUTION: shut off all breakers, and try to use short jig saw blads, and drill bits. I did actually hit a wire with the drill, whoops. I will be able to fix it when I get all the drywall out. Does that make sense? Check out the pictures.

Man, congrats your moving quick!!! In addition to above: "Drywall hand saw" = keyhole saw And only my opinion... :oops: I wouldn't bother drawing that many lines, especially with the hand held keyhole saw. Once you've found the studs and marked a corner or two with a drill, I would (and have) cut keeping pressure against the stud as I cut for a guide. This does make a really straight line. I would not use the jig saw for fear of cutting into a stud or plate, although I'm very found of power tools... this is one area where I would not use one. I would want to "feel it" when I'm close to cutting something I don't want to. Plus drywall is pretty easy cutting, but I'm sure a large amount of cuts will wear anybodies arm out. Even more fun is cutting 1/2" GreenBoard with 1/2" of stucco. :D apexer, I don't mean to come off offensively, just wanted to add my opinion. Thanks for posting the pics on this topic as I'm sure this will help many of us try and recycle some good drywall. Marc

Very impressive approach indeed. I would also caution against the use of the power tool though. Note that your nicked electric wire (presumably Romex) probably needs to be spliced in an accessible junction box now to meet code. Check with your local building department. --Keith :mrgreen:

sharward wrote:

Very impressive approach indeed. I would also caution against the use of the power tool though. Note that your nicked electric wire (presumably Romex) probably needs to be spliced in an accessible junction box now to meet code. Check with your local building department. --Keith :mrgreen:

And note that this accessible box has to be installed in your new inner wall - it can't be in the outside bay. Rod

Hi Rod... I quoted the reply below to give you reference... My question concerns what you said at the end... "And you do not waste your money using RC if you build double walls or even with staggered studs." Specifically about the staggard stud assembly. I posted this earlier... http://www.johnlsayers.com/phpBB2/viewt ... 9839039745 and in it I seem to get that a staggard stud with rc is better then one without. I am a little confused. I am forced to not build a double wall, so I am looking at either a single wall with rc OR staggard stud. In my post I got a great site from sharwood concerning stc in different wall assemblies (see sharwood's reply in my post) and comments about rc WITH staggard studs. I am going with staggard studs instead of single wall, but I do not want to waste money on rc if it is truley a waste. Please help me out here.... thanks...jam

rod gervais wrote:

camistan wrote:

To achieve better sound isolation, you will have to build another "room within a room" (as you stated) and decouple the walls/floor along with RC on your walls. (as SonicClang talked about) By doing this, I would think you would then have a "double wall construction". Only thing is, your "outer" walls (the walls already constructed) will not give you significant sound isolation. (That is unless you play your speaker volume REAL low) If you build another "room within a room" the walls that you build will have their own M-A-M rating depending on how they're constructed. (Maybe a "staggard wall" with 2 sheets of drywall on one side and 2 sheets of drywall on RC on the other side is appropriate???) You are right to say that there should only be 1 air gap per a M-A-M wall, but remember that's M-A-M "PER wall". Hopefully I'm correct in my thoughts stated here. If I'm not, I'm sure the moderators or other more experienced people will step in and correct me.

Consider yourself corrected........ WRONG - WRONG - WRONG. In construction built with 2 wall frames seperated by an air space - that is considered one wall. You never EVER put anything on the layer between the 2 wall faces - other wise you create triple or (in your case) quad leaf wall assemblies. So even if it's 2x4 8" air 2x4 - (so 15 1/2" outside face to outside face of framing) you would only sheath the 2 outer faces to maintain a 2 leaf system. And you do not waste your money using RC if you build double walls or even with staggered studs. Rod