need more mass....More sheetrock or Vinyl/Lead barrier ?

Posted: Thu Apr 05, 2007 7:20 am

I am in the sheetrocking stages of building my new studio.
I have just completed the second layer of sheetrock on the walls and ceiling in the large ( approx 18' x 22') tracking room. I am using 1/2 in sheetrock with Green Glue in between (75% coverage). I plan on a third layer of sheetrock and more green glue, but before I do that I want to know if sandwiching a layer of a vinyl/lead barrier in between the 2nd and 3rd layer will cut down on low end transmission through the walls. After the 2nd layer went up I had a friend play a floor tom in the big room and was able to hear low end transmission outside the building. Since that side of the building is about 20 feet from my neighbor, this is important to me.

What is better in controlling low end transmision, a 4th layer of sheetrock, or sandwiching a vinyl/lead barrier between the 2nd and 3rd layers of sheetrock ? I am using Green Glue in between all layers of sheetrock (Thanks Rod, this stuff is amazing !)

Some background: from the outside in, the structure is vinyl sided, 3/4 in plywood, 2x6 studded walls with a layer of R-19 insulation, 4 inches of dead air space, 2x4 studded walls with R-13 insulation, and so far 2 layers of 1/2 in sheetrock with 75% green glue coverage between layers.

Hopefully I am panicking too soon, but I want to be sure I am doing the best thing possible before I put up that 3rd layer in terms of low end transmission.

thanks in advance

Steve

Posted: Thu Apr 05, 2007 10:30 am

Steve,

Yer prolly gonna' just HATE me... but what I'm doing is 3/4 mdf on the studs... THEN 2 layers of gypsum w/Green Glue...

I would think that the Green Glue would do better than 1/8" MLV... at least that's what I thought the tests showed. The mass of a regular 1/8 pb (lead) sheet would definitely be better mass... but I don't know about the cost/performance ratio. However, I would think 1/8" pb sheeting would be as cheap as 1/8" MLV... possibly cheaper.

X

Posted: Thu Apr 05, 2007 3:35 pm

MadMax wrote:

Steve,

Yer prolly gonna' just HATE me... but what I'm doing is 3/4 mdf on the studs... THEN 2 layers of gypsum w/Green Glue...

I would think that the Green Glue would do better than 1/8" MLV... at least that's what I thought the tests showed. The mass of a regular 1/8 pb (lead) sheet would definitely be better mass... but I don't know about the cost/performance ratio. However, I would think 1/8" pb sheeting would be as cheap as 1/8" MLV... possibly cheaper.

X

Folks,

lead sheeting is more expensive than MLV - quite a bit more in fact.......

1/8" lead weighs 8psf....... as mass that beats the hell out of MDF and MLV together.....

The MDF in your case Max is doing a chore that is a lot more benificial than just mass......... it plays the role of providing structural bracing - which is why you don't have a single connector between your outside shell and your inner shell.........

In the case of this room - I'm sad for you Steve that you began with 1/2" drywall - the added mass of 5/8" type X board over 1/2" gyp is a big bang for the buck.......

The 5/8" mdf (at this time) won't give you any structural integrity - but it's always nice if you want to be able to hang anything anywhere your heart ever desires........ plus - it makes it less important exactly where your drywall joints break - because it doesn't have to be over the center of a stud (vertically).

That having been said - your least expensive route would be to add more drywall - 5/8" this time......... with GG -

You can't compare the cost preformance of MLV with GG - it just looses hands down.....

I wish yu had added mass to the inside face of the outside wall before building your inner shell - you threw away a great deal of isolation by letting that slide by you............ you literally threw away being about 6dB greater isolation than you are now - and you'll have to add 2 layers on the inside face just to equal what you could have at this point in time............

Sincerely,

Rod

Posted: Thu Apr 05, 2007 6:42 pm

Rod,

Kinda' surprised, yet not, that lead sheeting isn't cheaper than MLV.

I could see where MLV might be more expensive from the aspect of manufacturing processes adding to the cost of producing it. But like I said I had no idea as to the cost. Live, learn... it's all good.

X

Posted: Fri Apr 06, 2007 7:59 am

Rod and Max,

Thanks so much for the advice.
I will add extra 5/8ths rock now.

a few questions:

Will 2 extra layers (these will be layers 3 and 4) be better in terms of controlling low end transmision ?
As for the Green Glue, will 100% coverage (2 containers per sheet) get me better performance than 75% coverage ?

As for the MDF, I wish I knew ! I will keep that in mind for future projects.

I am also a little confused about the following:

Quote:

I wish yu had added mass to the inside face of the outside wall before building your inner shell - you threw away a great deal of isolation by letting that slide by you............ you literally threw away being about 6dB greater isolation than you are now - and you'll have to add 2 layers on the inside face just to equal what you could have at this point in time............

I guess I don't understand what is meant by 3 leaf systems.
Doesn't a layer of rock on the inside of the outer wall make it a 3 leaf system ? or does the outside layer of 3/4" plywood not count as a "leaf" ?
Please clear this up for me as I will be building more in the future.

Thanks again for your time and knowledge

Steve

Posted: Sat Apr 07, 2007 7:54 am

Jankland wrote:

I guess I don't understand what is meant by 3 leaf systems.
Doesn't a layer of rock on the inside of the outer wall make it a 3 leaf system ? or does the outside layer of 3/4" plywood not count as a "leaf" ?
Please clear this up for me as I will be building more in the future.

Steve,

I may be wrong, and if I am, I hope someone will correct me. But as far as I know, a leaf is an entire assembly that acts as one cohesive layer of mass. It acts as one cohesive layer by the fact that the sub-parts are tied together through some means of fastening... e.g., nails, glue and/or screws.

This is certainly a challenge of communication in a text only format... but I'll give it a whirl. If you had affixed the "mass" to the inside face of the exterior material, in the stud cavity, it's attached to the outer leaf.

Lemme see if this will explain it...

Your (typical) Existing Structure...

1. Exterior Layer (siding)
2. Vapor barrier
3. Fiber Board
4. Sheathing
5. Stud wall filled with insulation
6. 4" Air Gap
7. Stud wall filled with insulation
8. Gypsum
9. Gypsum

This is a two leaf system. Leaf one is comprised of items 1-5. Leaf two is comprised of items 7-9. The air gap is what designates the break between the leafs. One air gap... two leaf, Two air gaps... triple leaf. The air gap is what acts as the spring in the M-A-M model.

If you had taken the insulation out of the exterior wall (5) and added mass to the 4/5 junction (between the studs) it would be part of the outer leaf.

Additionally, as Rod pointed out, if you had put a layer of mdf on the interior stud faces (7/ Cool

, you get mass AND structural benefits.

As to 100% v. 75%... I honestly haven't dug that deep into their data yet. My guess is that since you started w/75%, that the transition to 100% would be an improvement. But how much TL/cost increase ratio... man... I dunno. You might want to contact GG directly and ask them.

Posted: Sun Apr 08, 2007 7:14 pm

Quote:

Additionally, as Rod pointed out, if you had put a layer of mdf on the interior stud faces (7/, you get mass AND structural benefits.

I believe max means in location 8 - with 9 and then 10 to be additional layers of drywall...........

Rod

Posted: Sun Apr 08, 2007 9:34 pm

Rod Gervais wrote:

Quote:

Additionally, as Rod pointed out, if you had put a layer of mdf on the interior stud faces (7/, you get mass AND structural benefits.

I believe max means in location 8 - with 9 and then 10 to be additional layers of drywall...........

Rod

Yes sir... I apparently didn't complete the thought/explination... my apologies if I caused any confusion.

Also, I don't know why the emoticon showed up either... rather odd...

hmmmm...

Posted: Mon Apr 09, 2007 5:25 pm

great. got it

thanks Rod and Max

I appreciate the help

Steve

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