Gap in the gyprock between wall and celling

Hello again all. I have just started part of my project early in my new home due to my mother-in-law who has one side of the house (soon to be walled off) wanting everything done yesterday less than a week after we moved in. I have stripped the cornice off her side of the wall before adding a sheet of gyprock soundcheck over the existing plasterboard and I have found something that I know is common but I am unsure how to proceed. There is a large gap between the ceiling plasterboard and the wall plasterboard (see pic) ... the gap goes into the ceiling space. Do I fill this? Do I cover it from the ceiling space with soundcheck offcuts? Do I leave it to be covered by the cornice again? Fill it with foam? Thanks in advance

The gap isn't your problem: the entire room is. Seal the gap with acoustic caulk if you want, but it isn't going to make much difference. And neither is the sheet of drywall you added. Best case, that might increase the isolation that you had before by maybe 3 or 4 dB: barely noticeable. The issue is the room. "Soundproofing" just one wall of a room is not going to accomplish much: you have to do the other five sides as well. You cannot "soundproof" a room by just treating one wall any more than you can build an aquarium by putting glass on just one side of the frame. It is an "all-or-nothing" proposition. Your mother-in-law may well be impatient, but no amount of impatience can cause the laws of physics to change (not even for a mother-in-law!).

who has one side of the house (soon to be walled off)

Once again, building a wall across the entire house is not going to help. Airborne sounds from your studio will simply bend around that wall, and structure-borne sounds will "flank" around it. The studio has to be fully decoupled from the rest of the house to prevent flanking, and has to be fully isolated on all six sides in order to prevent low frequency airborne sound wrapping around. Obvious paths in that photo (aside from the huge gap) are the electrical box in the ceiling, the ceiling itself, and the door. All of those are big issues, without even being able to see the rest of the structure. Sorry to be the bearer of bad tidings, but what you mother-in-law wants simply cannot be accomplished overnight, and certainly not in the way this is going right now. - Stuart -

I have had to start on this wall earlier than I had hoped.. im not just adding one extra layer of plasterboard to one wall, I have already removed the plasterboard from the inside of the room on the other side of the wall shown in the picture and I will be doing a room within a room in there. The gap does not effect that room within a room that I am building as such so I did not mention it but that wall is part of the room outside the room that that I will be building the room in a room within ... if that makes sense???

OK .... so here is where I am at ... I have added extra sheets of soundcheck plasterboard to the wall ( see pic) this is one of the rooms ajoining the room that I am sound proofing. This wall is forms one part of the outer leaf of my room within a room. The other side of this wall is exposed and ready for batts that you can see in the right of the picture. But I still have no idea what to do with the gap at the top of the wall where the ceeling sheets do not meet the wall ... should this be filled? Once again the room that I am talking about is not the room that is being soundproofed but the ajoining room. Thanks for any advice

Hi Fiz, Specifically for your question about the gap, if the wall extends up beyond the height of the ceiling as it appears to in the last photo you posted, you may be able to poke backing rod in there & caulk it. Otherwise, if you can get access to it from above, you might be better off beefing it up with strips of gyprock from up there. Watch out for snakes, they reckon 1 in 3 roof cavities in Queensland has a python in it :) The main point is that the part of your outer shell with the least mass determines the isolation, so make sure it's not that corner. The best supplier of backing rod (and sikaflex, caulk etc) I've found on the GC is Waterproofing Warehouse at Bundall. They sell backing rod by the meter in lots of different diameters, up to about 30mm.

Thanks for the info on the backing rod. I will be able to pop that in from the celing space. I have added a layer of sound check to the celing in the garage and to the walls of the rooms backing onto it. Now I can start building the framework for my room within a room. Its nailgun time.