Adding additional layers of drywall ?

Discussion in 'Studio Construction & Acoustics Forum' started by encephalon, Jun 29, 2003.

  1. encephalon

    encephalon

    Joined:
    Apr 23, 2003
    Likes Received:
    0
    Location:
    Napa, CA
    What's the best way to fasten additional layers of drywall?

    1. Screw into the layer below (will that hold)?
    2. Long screws into studs (will that short out the noise reduction)?
    3. Some sort of glue? (strong enough)?

    Thanks.
  2. Rod Gervais

    Rod Gervais Moderator

    Joined:
    Jun 8, 2003
    Likes Received:
    1
    Location:
    Central Village, CT
    Place the next layer of drywall at least one foot above the base sheet - and ideally 4' from the edge joint - make certain to fall on stud centers left to right and fasten with screws directly into the studs.

    It's the mass you're looking for - the screws into the stud will have literally no effect in sound transmissions.

    The reason for the offset from the base sheet (up/down and left/right) is to minimize the potential for sound transmission through the sheet joints - it also makes the wall assembly stiffer.

    Happy Hunting

    Rod
  3. jazzman_in_pa

    jazzman_in_pa

    Joined:
    May 12, 2003
    Likes Received:
    0
    Location:
    Philadelphia
    Home page:
    Adding another sheet of drywall directly on top of the existing layer into the existing studs will get you maybe an additional 2-3 dB of transmission loss. I did that on one wall between a bedroom and a kitchen, and I was disappointed that the difference was so small.

    To really start making a difference, consider removing - yes removing - the existing sheet of drywall (heck it's only $6 a sheet), and using either resilient channel or RSIC-1 isolation clips and hat track, and attach your two layers of 5/8" sheetrock into the channel or track, avoiding the studs altogether. Your isolation will dramatically improve, because your new drywall is effectively on a spring, and is no longer conducting sound directly through the screws and studs to the drywall on the other side.

    Lee
  4. Rod Gervais

    Rod Gervais Moderator

    Joined:
    Jun 8, 2003
    Likes Received:
    1
    Location:
    Central Village, CT
    Lee is right about the additional STC gained by RC channel - minimizing the direct connection points between the face of the drywall and the studs - and if you want to improve it even more - utilize a vinyl barrier before installing the channel,

    check out the barriers at:

    http://www.silentsource.com/barriers-soundbarriers.html

    Happy Hunting

    Rod
  5. sugarshed

    sugarshed Guest

    It has been our experience that the best method for true isolation may be ISDN. Seriously, for room to room isolation, mass is not the only issue. There is limp mass and rigid mass. Rigid mass will always resonate at some frequency. Limp mass is only so limp or so massive without #10 sky hooks.

    We went with two stud walls with two exterior layers of sheet rock (glued and screwed) with air space and insulation between the studs. I heard somewhere that 2x5/8" rock is the min req. It works well but is only as strong as the door, floor, ceiling etc. After all the work and expense, we still mute the sub when tracking drum or bass.

    I don't know any stats on spacing of layers, but basically I understand that you should stagger the seams, seal the joints between sheets and between the subfloor and ceiling. Unless you have some barrier (significant mass / vacuum) between two walls you will transfer the resonating freq to the next room.

    Best Regards,

    Wes
  6. encephalon

    encephalon

    Joined:
    Apr 23, 2003
    Likes Received:
    0
    Location:
    Napa, CA
    Thanks all for your help and suggestions. Special thanks to Rod for answering my question so quickly. I posted, made a run to Home Depot, and the answer was waiting for me when I got back!

    To everyone else, I think I need to specify what I'm doing. DIY sound room/iso booth construction is a study in compromise to say the least. I have decided to compromise on the isolation factor (more on that in a minute) in order to achieve the best sound inside the room. All the isolation in the world won't do you any good if the room sounds like shit. I'll take the occasional diesel truck outside the house over a boxy sounding room.

    So here's what I've done/am doing:

    8'x10' iso booth inside the garage. It's all framed, and the wall that is closest to (6") the outside wall of the garage already has 2 layers of 5/8" green board (the really heavy stuff) glued and screwed (thank you, Rod). I had to frame this on the floor, lay the drywall and then lift (give me a large enough lever and I can move the world =) it up before I could frame the other walls. Adding sheetrock to the other walls will be much easier.

    The floor is 6" deep. 2x4 joists, R13 isolation, 3/4" MDF, 5/8" drywall, 1/2" plywood. It's shimmed level, but I didn't bother to put down rubber as I don't know what the final weight will be. This is a really quiet floor.

    The walls are 2x4, and will have (at least) 2 layers of drywall on the outside of the frame. Here's where the compromise comes in: I decided to use the space in the walls for acoustic treatment, a la Ethan's trap and absorber designs. Instead of the 1x4's and 1x3's, I'll frame them inbetween the studs, which are 24" on center. I added 2x2 studs inbetween (12" on center) for added support for the drywall.

    The reason I am able to give a little on isolation is that this is really a room within a room construction. My control room is upstairs (not in the garage), so there are no isolation issues between the two studio rooms. I merely want to avoid sounds outside the house, and to prevent my practicing (piano, harp, tin whistle) from bothering the neighbors.

    The decibel system is not arithmatic. Adding a layer of drywall to an existing wall may not yeild great results. But the difference between a two-layer external wall and a one-layer wall is very significant. I may add more layers with resiliant channel if I need to, but I'm going to live with 2 layers and see what happens before I put the "finish" on the outside wall of the booth.

    So there you have it. I'm videoing my progress, and if I have time, I'll post some stills so you can all see how it's going.

    Again, thanks for all the amazing advice on this board. Seriously, I would not be able to accomplish this feat without all I have learned from you all.
  7. jazzman_in_pa

    jazzman_in_pa

    Joined:
    May 12, 2003
    Likes Received:
    0
    Location:
    Philadelphia
    Home page:
    Ceph, here's a cheap suggestion: When you're at Home Depot picking up the drywall for that second layer, stop by the roofing department and ask them to show you some GAF Tri-Ply. It weighs about .8 pounds per square foot and feels a lot like vinyl barrier but only costs about 20% as much as vinyl. From the feel of it I bet it would work a lot like vinyl as a decoupler and added mass as the middle layer between two sheets of drywall. Cheap but thin mass.
  8. encephalon

    encephalon

    Joined:
    Apr 23, 2003
    Likes Received:
    0
    Location:
    Napa, CA
    Jazzman,

    Thanks for the suggestion. I will definiately try this out.
  9. Eddie

    Eddie Guest

    There is a specialty screw called a laminating screw that will allow you to attach layers of rock directly into the existing sheetrock and bypass the studs all together. The screws will self-countersink and can be finished just like standard screws. Just run a few beads of adhesive and screw away, stay away from the studs!
    Have fun.
  10. Rod Gervais

    Rod Gervais Moderator

    Joined:
    Jun 8, 2003
    Likes Received:
    1
    Location:
    Central Village, CT
    Eddie,

    Great post........ :tu:

    I've never used those in a commercial application - so they never even came to mind.

    Happy Hunting

    Rod
  11. Rod Gervais

    Rod Gervais Moderator

    Joined:
    Jun 8, 2003
    Likes Received:
    1
    Location:
    Central Village, CT
    Jazz,

    One way or another we're going to wind up with someone trying that - and find out what a difference it makes - but in order to really know - they would have to construct without it - and then reconstruct with - taking readings before and after - to let us know the results. Otherwise they may just spend money thinking that they're getting better results - when it fact it makes little difference.

    Where is my crystal ball when i need it? ;)

    I mentioned in the last week or so that this material may very well work - however there is no test data on it due to the fact that this is not it's manufactured purpose. Thus it's never been tested.

    Perhaps if we can find out the exact material properties = and compare that with the vinyls which have been tested - we could make a determination.

    Anybody out there have connections with the GAF engineering department?

    Have a great weekend Jazz,

    Rod
  12. jazzman_in_pa

    jazzman_in_pa

    Joined:
    May 12, 2003
    Likes Received:
    0
    Location:
    Philadelphia
    Home page:
    Tell you what, Rod. I'll volunteer to do the testing. It won't be an official test, but it will be 64 square feet, and I'll have a good environment for it, an actual room in progress. Here's what I'll do. When I get to the point where the room is ready for it, I'll build angle traps into the four corners of my control room. First I'll test with the room empty and see what kind of frequency spectrum readout I get. Then, before I build the soffits, I'll mount angled broadband traps across each of the four corners of the room, with a 2-ft wide face, 8' high in the front corners, 4' hi in the rear corners, and 4' wide by a 2' tall face where the back and front walls meets the ceiling. In each case I'll mount a sheet of 1" 703 just behind the membrane but not touching, to broaden the response. First I'll try the Tri-Ply across the front, then 1/8" vinyl, and finally 5/16" plywood. All membranes will therefore have about the same density and should have about the same center frequency. I can probably get to this in about a month. Should be interesting.

    Rod, have a fine fourth, and a fifth on me.
  13. Rod Gervais

    Rod Gervais Moderator

    Joined:
    Jun 8, 2003
    Likes Received:
    1
    Location:
    Central Village, CT
    Jazz,

    Excellent, i'm excited to see the results.....

    so for the rest of you folks - let's see where this goes - maybe we have an inexpensive solution to a sometimes expensive problem.

    Jazz - i'll be waiting for that 1/5th. lol

    Happy Hunting my friend.

    Rod
  14. Eddie

    Eddie Guest

    Rod we used the laminating screws when the prints call for a 2 hour fire wall on metal studs. They work great, just put um anywhere you want to.
    I've thought about trying the GAF product myself,there is also another underlayment called weather sheild (I think) I forget who makes it. Even thought about using modified bitumen if I could find some cheap. Seems like any of this stuff should help some, but how much?
  15. jazzman_in_pa

    jazzman_in_pa

    Joined:
    May 12, 2003
    Likes Received:
    0
    Location:
    Philadelphia
    Home page:
    Eddie,

    A guy at GAF told me over the phone to get their Liberty Base/Ply product for this application (sticking to drywall). It's already got an adhesive backing you pull off, comes in 200 square-foot rolls one meter wide, and costs about $80 a roll. It's only weighs about .4 pounds per square foot, is 1/12 inch thick, and works like ice and weather shield. Rod points out that this stuff is untested in acoustics apps, so it's go at your own risk. Since I've put vinyl barrier up on ceiling joists, I know what a pain it is to work with, and I can imagine that a light adhesive roll that you can just roll up from the bottom of the wall to the ceiling would certainly be easy to install. And if it's waterproof, you know it's going to be airtight.

    Lee
  16. Rod Gervais

    Rod Gervais Moderator

    Joined:
    Jun 8, 2003
    Likes Received:
    1
    Location:
    Central Village, CT
    Eddie and Jazz,

    I suppose it would seem in theory that anything would help - Logic sort of dictates this -

    yet we know for a fact that arbitrarily adding sheets to STC rated assemblies can actually DECREASE their STC rating - (for example - adding sheets (ie: mass) to the inside face of one of 2 walls within the air space) - so Logic doesn't always work when it comes to sound isolation.

    One thing about the GAF Product - you will not have to worry about seaming the product - this stuff really sticks -

    So i am back to - give it a shot- and then let the people here at RO know what happens.

    Eddie - one other thing - what is the UL Assembly Number for the walls you're building - I've never seen one that indicated the use of thos screws. I want to check it out.

    Thanks

    Rod
  17. Eddie

    Eddie Guest

    Rod that was a commercial job that I did about two years ago but I think I've still got the prints here somewhere.I'll see if I can find them and give you more details. All I remember at this point is the walls seperated a huge conference room from a corridor with more smaller rooms and the walls were done with fire code rock and fire taped at the upper deck.
  18. Rod Gervais

    Rod Gervais Moderator

    Joined:
    Jun 8, 2003
    Likes Received:
    1
    Location:
    Central Village, CT
    Eddie,

    I'd appreaciate that - the only reason being - a lot of times something slips by me - but also - quite often someone gets something in their mind - and when done - they really don't maintain the rating of the wall assembly.

    For example - very few people actually staple the insulation to the back of the drywall in double stud wall UL rated assembly - they use a slightly wider insulation intended for a "friction fit" - yet some of the UL Testings were done with the insulation stapled (they take this into account when they test for STC Purposes) at the 4 corners and center of the bay - and if the insulation is installed in ANY OTHER MANNER than indicated in the UL Test results - the wall is not then a "Rated and Tested Assembly". It may seem "silly" but something as simple as that voids the firewall.

    It may also seem just as silly - but changing connection points in an STC assembly - means you have a wall that is no longer STC rated. It may appear to be better - and in fact may even BE better - but you have no way of knowing.

    That's why i am imterested in the UL # - having never seen this system used before.

    The going joke in my company is that i will die of boredom if i ever become a building inspector - because no one would ever want to build in my town. I look for too much of the little details.

    Happy Hunting

    Rod
  19. goldstar

    goldstar Guest

    Regarding the laminating screws Eddie talked about above: are you sure they weren't going into studs or at least into plaster and lath? I just went out and tried a few and can't get them to countersink (small ample , for sure; I used 1/2" rock, maybe the fiberglass threads in 5/8" type X grab better). I've seen these used in some of the remodelling work I do to lam. new DW over old plaster and lath; the thicker shaft of the screw helps keep them from shearing off when driven into the old lath. I haven't seen them used to screw one sheet of DW over another without backing, but then again, you learn something new every day.

    Frank
Similar Threads: Adding additional
Forum Title Date
Guests Adding mic input Jun 26, 2013
Media Production Adding video capabilities to your studio Mar 12, 2013
Digital Audio What recording gear are you adding in 2013 Dec 31, 2012
Hybrid Mixing, Summing Forums Adding a passive summing box to a MixDream Oct 19, 2012

Share This Page