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When adding a second layer of drywall to a ceiling, do I need to screw the first layer to the surface with the appropriate number of fasteners ( type S screws into resilient channel ) as code dictates or will the fasteners from the second layer puncturing the first layer suffice?

Full info

Two layers of 5/8" type-x drywall w/ green glue attached to 1/2" double-leg resilient channel. The first layer uses 1" Type-S screws while the second layer uses 1 5/8" Type-S screws.

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  • Why are you using two layers of 5/8" drywall ? Green glue ? The holding power of screws into drywall alone is next to nothing, I would guess that you absolutely need to attach to structure. – Alaska Man May 18 at 20:57
  • AM, the two layers of drywall is a common mechanism for sound-proofing. The green glue is placed between the layers as a decoupling membrane for sound vibrations to be dissipated through (It's not actually glue at all, which can certainly be confusing). The screws from both layers are going into 25 gauge resilient channel (thus the reasoning for the type-s bugle head screws and not type-w). Isherwood is correct, I'm just curious if I need to fully screw the first layer of drywall into the channel or if the screws from the second layer will have adequate holding power for both sheets of 5/8s. – Jason Reed May 18 at 21:37
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Yes, both sets of screws are required.

Two layers of gypsum board is generally used for two hour fire wall protection. The protection (and rating) comes from the proper installation, including proper nailing for both layers. If a fire develops and causes the top layer to fall, then the second layer would not have approved fastening to develop the two hour rating.

If the second layer is used for sound control, then no, the additional fastening is not required. (Sound control is developed in the material, not the fasteners.)

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  • Thank you for the reply, Lee. This is a basement remodel where the residential code mandates only a 30 minute burn time for fireblocking between levels. The install for both sheets is strictly to limit acoustical transfer. I'll double check with our inspections department but this is what I needed to know. Much appreciated. – Jason Reed May 18 at 21:47
  • If you install minimum number of fasteners in first layer, don’t wait long to install second layer with correct number of fasteners or the first layer could sag causing the final layer to sag when installed. – Lee Sam May 18 at 22:35
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I am going to point out that I do not approve the additional layer of drywall for ceiling. I just answered a question here - Should I use 1/4" drywall to cover ceiling texture or imperfections? - that addresses my concerns with an extra layer of drywall on ceilings.

I love doubleing up drywalls on wall (vs furring out) so I am definitely "liberal" on using drywall. I just don't like the extra weight and have had to go back and repair in the past. Add on a basement - the movement above - has to make it worse. I understand the doubling for noise but is that providing a better solution than stuff the joists with mineral wool? Also with a double drywalled ceiling... lights, fans, boxes become more complex.

Now I will just answer your question. No you don't need a normal screwing pattern. 16 screws per 8' is enough - but the key is to glue to the joists. I would also double screw the bottom layer in. This is a technique where you use the same screwing schedule and set screws about 1.5-2" apart for each pop. So everywhere you would put one... put two. It is a given that you will need longer screws to match depth of the drywall above and yes I would glue this too.

But to answer your question there isn't a rule for a set schedule in this place because it is still screwed in by the other screws.

I have done a lot of sound proofing work. I never saw a company that offered to double drywall. I am not saying it doesn't help - but between "sound proofing" guys, green companies, drywall crews, and general contractors I have worked with I think one of them would have brought this up (I have done A LOT of basements) if it was something that was worth it. The fact is you are making your install harder and making future issues harder to fix/troubleshoot. Seems the focus should be packing the cavity.

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  • Thanks for the feedback and yes I agree that my time would have been better spent packing the cavity with mineral wool, which is why I did that first ;-). All things considered, the STC rating will be 65 between levels and at a cost of only $1800 in additional materials. Yes, I have added more work for myself but In the end it isn't about making the job easier, it's about no compromises in the finished product. That being the case, I'm confident in our chosen solution and appreciate your insight into the original question. I will certainly double up screw placement for the final layer. – Jason Reed May 19 at 1:17

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