Point of using a ledger board when adding mass to walls?

[Quint]

Hi guys,

I've been adding mass (two additional layers of 5/8" sheetrock) in the bays between each set of studs on my preexisting walls. I know that in Rod's book he provides a diagram that indicates the use of ledger boards to permanently hold the additional sheetrock in place.

Here is my question, what is the purpose of these boards? Are they simply to provide a means of holding the sheetrock in place or are they also intended to provide additional mass over the caulked gaps between the sheetrock and the studs?

I ask this because I've read on this site that caulk (I'm using white GE 100% silicone) is about double the density of sheetrock so, if you're applying it properly in the gaps, this should provide all of the mass necessary to equal that of the sheetrock itself. After having read that, I'm inclined to think that no additional mass provided by the ledger boards is necessary because the caulk should give me all I need. I've been just screwing the sheetrock directly to the outside wooden siding along the edge of the sheetrock as close to the existing studs and top and bottom plates as I can get it. This essentially provides the same function as the ledger board, as far as holding it in place is concerned. If these boards are not intended to also provide some additional mass component, I'd prefer to not even add them.

Does anybody have any opinions on this? Do I need to use ledger boards for the purpose of adding additional mass along the gaps or am I fine not using them?

[Soundman2020]

I'm not sure I understand: I think you might be mixing up your terminology. A ledger board is a horizontal structural member attached to the face of a wall that supports joists. It is usually used to add a deck or carport roof to the vertical side of a house, like this:

Ledger-board-3.jpg

Ledger-board-2.jpg

I certainly hope you are not using ledger boards to hold your drywall in place!

I've been just screwing the sheetrock directly to the outside wooden siding

Bad idea. Take out those screws now, and do it properly. You should not have any screws going into your siding! And you should also not have any hard attachment of the "beef up" drywall to the surface behind it. The drywall needs to just sit there, in contact with the existing leaf, but not attached to it, in order to act both independently and jointly with the rest of the leaf. Multiple point attachments reduce the isolation. The Wyle Report explains what that does, if you are interested in the theory and empirical testing.

Does anybody have any opinions on this?

My opinion is to do it the way Rod says! In general in acoustics it's not a good idea to do something in an entirely different way just because you didn't like the way everyone else was doing it... at least, not unless you have a solid understanding of the underlying acoustic principles, and how they will be affected by what you decided to do.

Do I need to use ledger boards for the purpose of adding additional mass along the gaps or am I fine not using them?

Ledger boards do not add mass: they support floors, decks and roofs.

I've read on this site that caulk (I'm using white GE 100% silicone) is about double the density of sheetrock so, if you're applying it properly in the gaps, this should provide all of the mass necessary to equal that of the sheetrock itself. After having read that, I'm inclined to think that no additional mass provided by the ledger boards is necessary because the caulk should give me all I need.

The purpose of caulk is not to add mass either: It is to provide a flexible, resilient air-tight seal. Yes, it also helps to maintain consistent surface density throughout a leaf, but that's a secondary benefit. The primary reason why you caulk things is to get an excellent unbroken air-tight seal.


- Stuart -

[Quint]

I'm not sure I understand: I think you might be mixing up your terminology. A ledger board is a horizontal structural member attached to the face of a wall that supports joists. It is usually used to add a deck or carport roof to the vertical side of a house, like this:

Ledger-board-3.jpg

Ledger-board-2.jpg

I certainly hope you are not using ledger boards to hold your drywall in place!

I've been just screwing the sheetrock directly to the outside wooden siding

Bad idea. Take out those screws now, and do it properly. You should not have any screws going into your siding! And you should also not have any hard attachment of the "beef up" drywall to the surface behind it. The drywall needs to just sit there, in contact with the existing leaf, but not attached to it, in order to act both independently and jointly with the rest of the leaf. Multiple point attachments reduce the isolation. The Wyle Report explains what that does, if you are interested in the theory and empirical testing.

Does anybody have any opinions on this?

My opinion is to do it the way Rod says! In general in acoustics it's not a good idea to do something in an entirely different way just because you didn't like the way everyone else was doing it... at least, not unless you have a solid understanding of the underlying acoustic principles, and how they will be affected by what you decided to do.

Do I need to use ledger boards for the purpose of adding additional mass along the gaps or am I fine not using them?

Ledger boards do not add mass: they support floors, decks and roofs.

I've read on this site that caulk (I'm using white GE 100% silicone) is about double the density of sheetrock so, if you're applying it properly in the gaps, this should provide all of the mass necessary to equal that of the sheetrock itself. After having read that, I'm inclined to think that no additional mass provided by the ledger boards is necessary because the caulk should give me all I need.

The purpose of caulk is not to add mass either: It is to provide a flexible, resilient air-tight seal. Yes, it also helps to maintain consistent surface density throughout a leaf, but that's a secondary benefit. The primary reason why you caulk things is to get an excellent unbroken air-tight seal.


- Stuart -

Actually, since I first started this thread, I read elsewhere in Rod's book that you COULD actually attach the sheetrock to the outside siding using screws so now I'm not sure what to believe. In his book he says you can forego the ledger boards if you are able to screw into the siding instead. To be clear, I'm ONLY placing the screws along the outside edge of the sheetrock at the same location where the ledger boards would be located.

So I'm having a hard time seeing what any appreciable difference would be? Whether it's screws or the ledger board, you're still restricting vibrational movement (and the resulting level of isolation) along the edge of the sheetrock so what's the difference? If I was placing screws down the middle of the sheetrock I could totally understand how that would reduce isolation but I'm only placing them along the edge where the ledger board would be anyway.

Also, to play devil's advocate, why are screws a "no no" when beefing up an existing wall but no problem when attaching sheetrock to new walls? With new walls, you obviously must attach the sheetrock to the studs with screws so I don't understand what the difference is? Shouldn't the same principle apply in both situations?

Speaking of ledger boards, this is what Rod calls them so I'm not sure what to say about that. He used the word "ledger", so I did too. I actually purchased some 3/4"x1 1/2" furring strips a while back to be used as my "ledger" boards but then had considered not using them after reading Rod's book (2nd Edition, page 272) again. So back to my original question, is the point of these boards (ledger board, furring strip, piece of wood or whatever else you'd like to call it) ONLY to hold the sheetrock in place or is it also intended to provide some additional mass along the caulk gaps? Based on our conversation so far and what I've read in Rod's book in the interim, I'm guessing NO. I just figured I'd double check that.

As for the caulking density issue, I actually developed my question about caulk density based on a previous post by you in another thread here. So now I'm doubly confused. In that thread, you specifically discussed the notion that colored caulk was double the density of sheetrock and that it ALSO served that purpose in addition to providing an air seal. I thought the air seal and density were of equal importance?????

For reference, here's the caulking thread you posted in:

http://www.johnlsayers.com/phpBB2/viewt ... =2&t=19519