To beef or not to beef - that is the question

In considering different approaches for my second build I have been thinking lately about how much labor went into the beef-up process (between existing ceiling Joists) in my last studio build, and whether the isolation to effort ratio would be increased by adding the extra two layers of mass to the inside leaf of the ceiling. I know that in a lot of basement scenarios this would not be realistic given the limited ceiling height available, but in my case I'm more concerned about a) adding extra weight to the engineered joists, and b) the increased speed with which one could install the extra layers, and perhaps c) the ability to avoid mistakes and also compromise where there are pipes or ductwork existing in the joist bay. I have about 94" available and am planning an independently framed ceiling. I spent a couple of hours looking around the forum elsewhere on the web and could find no discussion on this so thought I would open it up. Please feel free to point me to existing content if you are aware of any. I have to imagine that there is good reason for not doing this else everyone would be doing this. Perhaps the imbalance in the mass of the two leaves, or not having enough mass in the upper leaf to minimize the impact / foot noise from above. Many thanks for your thoughts... Btw my thread can be found over here on the design forum.

Apologies for the bump, but it wondered if perhaps my question was missing some detail or slipped through the cracks with the holidays. Or maybe my questions is just too dumb :oops: Hope everyone had a wonderful holiday and wishing you all a prosperous and rocking 2014! Andy.

Happy New Year Andy!!!! :) OK, the principle behind MSM isolation is that there are two leaves with roughly the same amount of mass on each leaf: That gives you the optimum, in terms of isolation. If there is substantially less mass on one leaf, then you no longer have optimum conditions. That's not to say you can't do it that way: just that it isn't optimum. The other issue is the seal: If the floor above you is already very well sealed, with no cracks between the sub-flooring panels, and no gaps around the joists or around the edges, and no other cracks, gaps, nooks, crannies, etc., then you are probably OK. Do you know how thick the OSB sub-floor is? One layer or two? And what is the final flooring on top of that? If you already have a two layers of 5/8" OSB for the sub floor, and something reasonably massive on top of that, then you are probably in the ball-park for decent isolation. - Stuart -

Happy New Year to you too Stuart! :) Thanks for the explanation which makes a lot of sense. Having gotten down in there and removed the existing ceiling recently I am able to see that what's up there right now is "Structurewood subfloor 23/32inch". I only see one layer. The flooring above varies from room to room. Above the family room is carpet, and above the kitchen and breakfast nook is hardwood flooring (not sure what was laid under the hardwoods - all of this was in the house when we bought it). I can tell you that with the old drywall down you can hear absolutely everything from upstairs; the TV on low volume, my 3 month old's baby swing as it clunks back and forth, I could probably even hear the dog fart if I gave her some brussel sprouts! :roll: Since I have TJI's I do want to get a structural engineer in to see how much extra load I can add for beef up. I feel pretty safe about adding one layer of sheetrock between the joists given that I just took one layer off the ceiling which will not go back up (I plan to frame the ceiling on top of the walls - may have already mentioned this but I'm pretty tired and would rather mention it twice than not at all), but would want a professional opinion on whether it is safe to add a) 5/8" (what I removed was 1/2"), and b) ideally two layers. I also want them to look at how the TJI's are sitting on top of the existing wall framing to ensure that it is not supporting any load. Ideally I would like to take all of the 2x4's out and repurpose them for my new walls, but again - an assumption I'd rather not make without a professional opinion. Hope you had a great holiday and thanks as always for your time, insight, and support. All the best, Andy

Sounds like you have a good plan there, and from what you say, I'd definitely beef up as much as possible (hopefully with two layers of 5/8), as well as sealing everything in sight. Looking forward to seeing some photos of what you have up there! :) - Stuart -