About to start hanging drywall - a few questions

[colliderman]

Hey all,

I'm about to start putting boards up on the walls and ceilings. I just want to describe my plan here, and ask a few questions to make sure I'm not missing any details or doing something incorrectly.

I've built two independently framed rooms (Control room, live room). Their ceilings have been built on their walls. The wall height is 10' and the stud spacing is 24" OC.

For the ceiling, the plan is:
- layer of 5/8" OSB
- layer of 5/8" drywall

For the walls, the plan is:
- 2 x layers of 5/8" drywall

I will start by putting the OSB up on the ceilings.

QUESTION: Should the OSB ceiling layer be up tight to the framing?

Next I'll do the walls for each room. I plan on leaving a 1/4 gap on all corners of the walls (wall to ceiling, wall to floor, wall to wall) and then filling with backer rod and caulk.

The drywall on the walls will be done vertically, both layers. This is mostly because of the 10' height, it just doesn't make sense to me to do it horizontally even though everyone seems to say that's the correct way to hang drywall. There will be much less linear footage of seams this way, even if they are harder to finish because they're vertical. Also, this will leave no butt joints to finish.

I will stagger the seems of the drywall - which leads me to my next question:

QUESTION: What is the correct fastening procedure for 2 layers of drywall?

I have been researching this and found some information about how to fasten but I'm still a bit unclear. I believe the fasteners should be spaced 24" apart, which is optimal for STL.

If I just put fasteners in the first layer as normal, then do the second layer in the same way, the first layer will end up with twice as many fasteners through it. Is this ok? If not, what's the proper procedure here?

Thank you for any advice!

[gullfo]

couple of thoughts - i generally line the entire room with 1/2" plywood (preferred) or OSB. then apply 2x 5/8" drywall. each layer (ply and gwb) seal all the air gaps. on the ply and first gwb, you can do a rough finish on the sealant. stagger the gwb - layer 1 vertical, layer 2 horizontal or vice verse. typically you would put the first layer fasteners on 12", and then the second layer fasteners also on 12" but alternating with the lower layer. this puts a fastener every 6". you could stretch this to 16" to get 8" spacing.

gwb layer 1 - using 1-1/4" screws, gwb layer 2 - using 1-3/4" or 2" screws. wet sand the joint compound to avoid "devils dust".


all layers are tight - ply to the frame is tight. gwb layers are tight.

some additional considerations - leave a 1/4" gap on the floor side gwb so you can get a good seal with backer rod and caulk. on the gwb layers, stagger the corners to form a "bank vault" and seal those with backer rod and caulk so each layer is sealed, and thus preventing leaks later is one fails (shifting, wet lumber shrinks, or dry framing get damp, etc.

[colliderman]

Glenn,

Thank you so much for your advice, it's incredibly helpful.

Regarding the first plywood layer, I was considering doing the first layer in OSB and had made a post about that here https://www.digistar.cl/Forum/viewtopic.php?f=5&p=7030#p7030 (which you again, helpfully weighed in on) but I've decided to do the OSB layer only on the ceiling as the first layer and then stick to gwb only for the walls. I know it's helpful to have a solid substrate under the drywall for attaching treatment and other things to, but I'm fairly confident that I'll be able to manage my acoustic treatment plan without it and will be able to hit studs when I need to. I may regret this decision down the road but we'll see!

Regarding the rough finish on the first gwb layer, does it need to be taped and mudded? In reading through the NRC documents on their testing I see that they caulked and then taped the drywall seems with "metalized duct tape". That seems quick and easy but I'll tape and mud if that's what I should be doing. I suppose the tapered seems should be filled in so there's no air pocket under the top layer where the tapers are on the first layer?

And you mention using backer rod and caulk on the corners of each layer - so then is my assumption that I should be leaving about 1/4" gap at the wall to wall and wall to ceiling corners (as well as the wall to floor as you mentioned) correct?

Thanks again!

[Starlight]

Source of the post... I'm fairly confident that I'll be able to manage my acoustic treatment plan without it and will be able to hit studs when I need to.

I am fairly confident that the ideal placecment and size(s) of your acoustic treatment will not always coincide exactly with your studs. However, you have had suggestions from Glenn and myself often enough that you are not making this decision without careful consideration, so all the best.

Source of the postI may regret this decision down the road but we'll see!

I really hope you will not have a reason to regret your planning decision further down the road.

Source of the postRegarding the rough finish on the first gwb layer, does it need to be taped and mudded?

My studio's designer, John H. Brandt, instructed me to use tape and mud on every crywall layer. Your designer (you and the internet) may decide otherwise. What I like about my designer's instructions is that every step includes a back-up, sort of an insurance, that if something is slightly amiss then I have done everything possible to keep the level of isolation intact. At the end of the day it is your choice.

Source of the postAnd you mention using backer rod and caulk on the corners of each layer - so then is my assumption that I should be leaving about 1/4" gap at the wall to wall and wall to ceiling corners (as well as the wall to floor as you mentioned) correct?

Yes, for each and every layer. What happens when, in 6 years, say, that something (a mild eathquake, perhaps) rocks your building and the join between two walls or a wall and the floor or ceiling is stressed to its limit? Would you want to have some small level of movement possible or would a small crack the length of the room and resulting sound leakage be acceptable? I chose to go the mildly paranoid route and ensure to the best of my ability that any movement would not be able to break the caulk joints and so my studio will retain its isolation. Again: your studio, your choice. Here is my studio's wall to floor join with backer rod being pushed into place with an old credit card.


PS. Anything Glenn says will trump my comments as he is the pro whereas I, like you, am merely building my studio to a pro's plans.

[gullfo]

using caullk and metalized tape (basically duct tape, the real kind) could be used. the joint compound and tape is usually less expensive, and on the inner layer only needs a rough finish to level it (again strongly recommend wet sanding (basically a medium 3M scrubber + water = smooth finish with some water drips) vs dry sanding (mesh or paper = devils dust and potentially months of cleaning)).

if your design has everything tighly locked, then you don't need to leave gaps on the wall/ceiling joins. but if you are decoupling or simply want to wall and ceiling panels to be slightly separated, then the backer rod and caulk.

the plywood all around helps make the structure more rigid (high resonances = easier damping later) as well as fasten anywhere, and any structural shift less likely to occur in a way which fractures the drywall or joints (think "shear wall").

[colliderman]

Thank you Starlight and Glenn! I appreciate everyone's advice and feel confident in proceeding now. Cheers!