[barry2020]

I am in the process of buying a house and I plan to put in a legal secondary suite in the lower level. I want to improve the ceiling downstairs for sound as well as fire rating (fire rating easier than sound I believe). I don't believe there is insulation between the joists downstairs so I am planning on tearing out the existing ceiling drywall. I will then put in insulation and will also put up 2 sheets of drywall.

My question is hanging the second sheet of drywall. I believe there is 1/2" drywall up there now and I assume it was put up before the walls. When I remove the ceiling I assume I can maybe slide the first new sheet of drywall (1/2") between the ceiling and wall boards (I would like to use 5/8" but I guess this would be too thick for existing gap). For the second sheet I will have to butt up against the walls as opposed to on top. Is this ok? I know it is recommended to have the wall boards push up against the ceiling.

As well would you recommend putting up furring strips first so that putting up both layers is easier in case hitting the joists is a problem? If I use furring strips then neither ceiling board will be on top of the wall boards. Also is 1" furring strips ok?

Or I should I try to cut 1/2" or so off the tops of all the wall boards so that all ceiling drywall can sit on them?

Any thoughts?

 

[lenaitch]

I think you will get better sound isolation by using resilient channels rather that double drywall, besides being easier. I don't know about fire ratings. Mineral wool ('rock wool, Safe and Sound, Roxul, etc.) will be your best best for insulation.

 

[dj3]

Also there is the weight factor of double drywall.

 

[RustNeverSleeps]

You might want to check out this series. I had watched one video out of this serious earlier this year...I think it was the one where Jeff was specifically making one sound proof room in a home, and found it informative.

https://www.youtube.com/playlist?list=PL34cQkzKfXWZtD4jIm86DQF1fhsHeXwpe

 

[mark sr]

When I remove the ceiling I assume I can maybe slide the first new sheet of drywall (1/2") between the ceiling and wall boards

If you are hanging 2 full sheets I doubt that would work well. While you could slide one side in [probably with difficulty] you wouldn't be able to insert the other side. I'd rather secure the ends better [maybe add framing] than fight to get the edge above the wall's drywall or have an unneeded seam in the middle.

 

[huesmann]

Any reason he couldn't just rotozip the walls a smidge shorter so the thicker drywall ceiling can fit over top? (Or equivalent tool—not sure if a rotozip can get in there with so little clearance.)

Although I do get your point about inserting the other side. Maybe you could get one of the sheets inserted on 3 sides using flex, though.

 

[barry2020]

Hi thanks for all the answers so far...very helpful.

I have been researching a bit more and am considering possibly going with the resilient channel and 1 layer of drywall (5/8" regular or possibly a sound proof option). I believe when you install with the channel, for sound proofing purposes you would want to leave a gap under the ceiling of about 1/4" so that the ceiling does not sit on the wall boards and therefore not being supported.

So in my case if I used the channel I guess my existing wall boards would be higher than my ceiling and I would hang my ceiling leaving a 1/4" gap between the edge of the ceiling board and wall board. Does this sound correct and will this work? Will this gap cause a fire blocking issue? Will I need to fill the gap...this could be tricky since filling vertically I suppose?