Attaching drywall between joists

[BilWare]

I've demo'd the basement space I'm hoping convert into a decent home studio. Like everyone else, I feel obligated to say (because it's true) that this is a fantastic resource for schmucks like me who hope to gain from the wisdom of those who've gone before us.

Here's my first, but probably not last, question:

I'm planning on beefing up the mass of the basement ceiling/kitchen floor leaf by adding drywall between the floor joists. But I can't find a definitive answer in the forums on how to attach. The latest suggestion I found was in Knightfly's diagram in his May 1 reply in this thread. It says "glued, screwed, acoust. caulked." I guess I wonder whether it's necessary to both glue and screw the drywall. How much, if any, isolation do I gain from the glue? And if it's enough to warrant attaching with both methods, how much glue to I apply?

Thanks for any help you can provide.

[goldstar]

BW

I think the main advantage with glue AND screws is the fact that you'll be screwing thru 5/8 or 1/2 inch material into something that's only (probably) 3/4 thick, so the screws wont have lots to grab if you use 1 1/8 or 1 1/4 screws. You don't want the screws to penetrate up thru the subfloor, so size them carefully for length (step on one poking up from underneath and you'll likely never forget it).

You won't gain more iso, just better attachment to the surface above. I'd use quarter sized spherical blobs of construction adhesive spaced 12-18" apart if it is kinda bumpy like 1x6 diagonal sheathing, or 1/4" beads spaced the same if it is plywood subflooring like a newer house (post 1970 or so). Good luck, because it is a pesky project to take on.

Frank

[sharward]

I also think there has been mention of screwing "cleats" to the studs (if wall) or joists (if ceiling) that serve to hold the strips of gypsum board firmly against to the surface being "beefed up." The cleats don't have to be large -- I think 1x1 was proposed. This is not a substitute for what has already been stated, but rather, a reinforcement to keep the strips in place.

Consider that a strip that breaks free partially could "short out" the leaves by forming a bridge between them -- the cleats virtually guarantee that won't happen.

[sharward]

In what I believe to be an absence of any single thread devoted to this topic (since it only seems to be mentioned in other threads), I hereby nominate this thread to be the official "how to do it" thread that we can continually reference when needed! Experts: speak!

[PhiloBeddoe]

I'm not an expert and there are probably several ways to do this, but here's what I did:

1. Verify that the size and span of your joists can safely support the drywall you are going to put between them together with any other loads, e.g. drywall and insulation you plan to add to the bottom of joists for your studio ceiling.
2. Measure gap width between joists.
3. Cut two 4'-0" long drywall (I used 5/8" thick drywall) pieces that are 1/2" less wide than the gap between joists, because you'll probably find that the gap is non-uniform and if you cut them too tight they won't fit. In my case, the joists were 16" on center, making the gap between them 14.5". I cut my pieces to be 14" wide. I used 4'-0" lengths because of the weight and manageability of installing them.
4. Glue the two 4'-0"x14"(in my case) pieces together on floor or table.
5. Cut two 1"x2" cleats to a length of 3'-11.5". I made them 0.5" shorter than the drywall pieces because I wanted a little play in installing them.
6. Predrill three 1 1/4" screws into each 1"x2" piece, driving them in only far enough for them to hold themselves in place. I put them in at a slight downward angle so they could be more easily driven in when installed, otherwise the chuck of your drill may contact the drywall. This step can be done on the floor/table and saves handling the screws while installing.
7. Run a bead of glue on the side of the drywall pieces that will be contacting the subfloor.
8. Get a helper. One person can hold the drywall pieces in place while the other drills the 1"x2" cleats into the side of the joists.
9. Caulk (using OSI SC-175 sound caulk or equivalent) between each 4'-0" section of drywall, in between bottom of cleats and joists, and in between cleats and drywall.

I didn't screw anything directly to the subfloor for fear that I would penetrate the floor upstairs, but there's really no reason you cant do that if you're careful.

I hope this makes sense, here's a picture:

http://www.johnlsayers.com/phpBB2/files ... avity1.jpg

[VSpaceBoy]

I didn't screw anything directly to the subfloor for fear that I would penetrate the floor upstairs, but there's really no reason you cant do that if you're careful.

Wouldn't driving a nail through the drywall into the subfloor leak vibration? I like the glue and cleat idea better. Of course this isn't from experience, just the physics.

[BilWare]

First, thanks for your replies. It sounds like this is more an issue of structural integrity than acoustics.

Which gets me to VSpaceBoy's observation, which was really what I was wondering in the first place - Why would screws in the ceiling/subfloor transmit significantly more (or less) vibration than glue or the cleat assembly? Don't they become part of the entire mass of the leaf as long as there's no air space? Won't cleats similarly transfer vibration to the drywall at every point of contact?

-Bill W.

[sharward]

The pros/cons of glueing vs. screwing multiple layers of sheet rock together has been covered in some detail within the "Complete Section - (Temporary 'FAQ')" thread, item #5.

Great "How-To" work there, PhiloBeddoe! Here's your photo, embedded within this post, to save folks a click:



For info on how to embed an image to a post, see the BBCode notes.

[VSpaceBoy]

Won't cleats similarly transfer vibration to the drywall at every point of contact?

It will somewhat but no more than the direct sound hitting the surface of the drywall. Puncturing drywall with a screw (metal conductor) into the subfloor above would work like fishing line between two tin cans.


sharward, looking at the above picture I have a few questions.

1 - Did you glue the drywall to the subfloor above, then secure the cleats?

2 - Counting on the cleats for the main supports seems like it could lend to problems if moisture ever built up for any reason. Do you think that could ever be a problem?

[BilWare]

Puncturing drywall with a screw (metal conductor) into the subfloor above would work like fishing line between two tin cans.

But if those tin cans are effectively back-to-back (mass-to-mass ==> one continous layer) then the transfer through the fishing line/screw would be pretty minimal, right? I mean, it stands to reason, I think, that you can't transfer significantly more through the screws in this arrangement than you could through the cleats, maybe a fraction of a db.

[VSpaceBoy]

The cleats are not in direct contact with the subfloor above. They are resting on the surface of the drywall.

[PhiloBeddoe]

VSpaceBoy,

In response your questions:

1. Yes, I did put glue on the drywall before lifting it into position between the joists. I wouldn't expect this to do much in the way of adhesion, but figured it wouldn't hurt and may provide some damping if there were any voids between the drywall and the subfloor above.

2. As shaward pointed out in his reference to the Complete Section, I wouldn't obsess over fasteners. This is really no different than fastening a drywall sheet to a wall frame or resilient channel. The drywall between the joists and the subfloor are the same leaf. There is a very long list of things to worry about before worrying about transmission through fasteners.

[VSpaceBoy]

..2. As shaward pointed out in his reference to the Complete Section, I wouldn't obsess over fasteners. This is really no different than fastening a drywall sheet to a wall frame or resilient channel.

The question was geared more towards the sagging of the drywall over time with no supports in the center. However you answered that question with gluing it. Seems solid to me.

.. There is a very long list of things to worry about before worrying about transmission through fasteners.

I'm not trying to argue, but thats not the impression I always get from Steve. (including in that sticky) I believe that why he went into such detail and then revisited and added to his own post.

You can overbuild an entire boat, but it'll still sink with one hole.

[Paul Woodlock]

I've demo'd the basement space I'm hoping convert into a decent home studio. Like everyone else, I feel obligated to say (because it's true) that this is a fantastic resource for schmucks like me who hope to gain from the wisdom of those who've gone before us.

Here's my first, but probably not last, question:

I'm planning on beefing up the mass of the basement ceiling/kitchen floor leaf by adding drywall between the floor joists. But I can't find a definitive answer in the forums on how to attach. The latest suggestion I found was in Knightfly's diagram in his May 1 reply in this thread. It says "glued, screwed, acoust. caulked." I guess I wonder whether it's necessary to both glue and screw the drywall. How much, if any, isolation do I gain from the glue? And if it's enough to warrant attaching with both methods, how much glue to I apply?

Thanks for any help you can provide.

Greetings

This is a simple job. Mass is the defining property. FORGET about anal screw and glue discussions

Simply cut your drywall so it easily slides between the joists, and screw them in with drywall screws. No need to use glue. just caulk between the drywall edges and the joists befoe adding the next layer. Succesive layers should overlap the previous layers joins.

That's it.

Disclaimer: Make sure the floor can take the weight.

Paul

[BilWare]

This is a simple job. Mass is the defining property. FORGET about anal screw and glue discussions

That is exactly what I wanted to hear. All you dissenters, I have my fingers in my ears and am singing the "Tomorrow" chorus from Annie, so as to evade whatever logic you would use to cloud my brain

Seriously, though, thanks for all your advice. This is a great resource for people like me.

-Bill W.