Framed floor transmission reduction.

I’m looking to build a 24’x26’ garage with a studio/practice space above it In Nashville TN. For the most part, I understand how to reduce sound transmission through the exterior walls and ceiling and I realize the only true way to reduce it through the floor is to make the floor concrete. Since this is not an option, I was wondering if there are any economic ways to at least reduce some of the sound transmission through a framed floor and then reduce it again as it transmits the walls and garage doors below.

If this is a rehearsal area, I'm guessing you will have live acoustic drums, bass amps, electric guitar amps and other loud things up there, correct? I'm afraid there is no "simple and cheap" way of isolating that situation. This is the main reason why the vast majority of studios are built at ground level. For the few that are built on an upper floor, they have massive concrete floors, or even floating floors. Isolation cannot be done with light-weight timber framing and decking. The laws of physics do not allow it. It's not that you need some type of special material to do it: it is that no such material can exist in this universe, because such a material is impossible, physically. Isolation requires two things, mainly: Mass, and decoupling. "Mass" means very thick, heavy materials, such as concrete, brick, ceramic, glass, steel, aluminium, etc. A couple of layers of plywood on a timber frame is way short of the amount of mass you need. You can get maybe one tenth of the required mass, if you pile on several layers of thick plywood... "Decoupling" means basically that you need two floors / walls / ceilings around you that are disconnected from each other acoustically, and have an air gap between them. In other words, for high levels of isolation on an upper level in a building (not ground level), you need a "floated floor". That is hard to do correctly, and expensive, and requires a lot of mass anyway. So if you cannot have a massive floor in your upper-floor studio, then you cannot have good isolation. Here's a thread that explains some of the issues with floating floors, mass, and high isolation: viewtopic.php?f=2&t=8173 Realistically, with the type of construction you seem to have, and some good drum risers / amp risers, you might be able to get 30-something decibels of isolation between upstairs and downstairs, perhaps even into the low 40's, but I would not hope for any more than that. - Stuart -

Again, I know a framed floor does not compare with a concrete slab, with regards to noise reduction. I just wanted to know how much if any it would reduce. Thanks for answering my question. To get that 30-40db reduction, would you suggest filling the floor with rock wool or regular fiberglass insulation and would you suggest the ceiling below be hung on resilient channel?

Again, isolation is a system, not a floor. Impact noise in the floor is flanking noise: if it is in the building structure, then no amount of isolation under the floor will prevent it from being heard outside. The outside walls of the building itself will re-radiate the sounds, completely bypassing whatever you happen to hang below the floor. IRC-RR-168 and IRC-RR-169 will probably help you understand the issues here, and why decoupling the floor is the only option. Hanging drywall from RC in the space below the studio will only help with airborne noise: that's the 30-40 dB isolation figure I mentioned. It will do nothing at all for structure-borne sound, which is by far the biggest problem in a light-weight non-isolated timber-framed floor. Basically, that is a drum head: it is a membrane that will pick up vibrations in the room, and transfer them directly into the structural members of the building itself (the studs): Since the framing of the entire building will then be vibrating in sympathy with the floor, whatever surface you have on the outside of the building (I'm assuming OSB with siding?) will act like a giant loudspeaker, and will radiate that sound in all directions, into the neighborhood. Drum risers can prevent direct impact from getting into the floor, but they cannot prevent the sympathetic resonance issues of the floor "drum head" picking up the airborne vibrations and flanking them into the rest of the building structure. Both of the documents I mentioned above show the mechanisms by which this works, and the results you can expect from various construction systems and isolation systems. However, since you will not have any isolation system, you are limited to what can be accomplished by construction alone, which is not very much. Again, there's a reason why studios are not built on upper levels unless the floor is either massive, or decoupled, or both (fully floated). IR-168 and IR-169 explain that reason, with real laboratory testing, and real results.

I just wanted to know how much if any it would reduce.

Basically, nothing, since that is not the path that sound is taking. It's like putting a roadblock on a minor side street that runs parallel to a ten-lane freeway, and wondering why your roadblock has no practically no effect on overall traffic flow. You have to block the freeway as well, if you want the side-street block to be effective. You can have the best roadblock ever erected on the side street, capable of stopping an entire army, but it will have no effect on overall traffic flow, since the ten-lane freeway is the easy path.

To get that 30-40db reduction, would you suggest filling the floor with rock wool or regular fiberglass insulation and would you suggest the ceiling below be hung on resilient channel?

Either mineral wool at 50 kg/m3 or fiberglass at 30 kg/m3 would do fine, and resilient channel is necessary, yes, with two layers of 5/8" drywall. Use Green Glue between the layers as well, for maximum effect. That would indeed constitute a very effective roadblock on the minor side-street.... :) Once again, the problem is not in transmission to the area below the floor: the problem is structural transmission, also called "flanking", through the floor itself and into the building structure, where it will be re-radiated everywhere. That's why floating floors were invented. They constitute a good roadblock on the ten-lane freeway. You might want to check out Stefan Schoenwald's paper from a couple of years ago, titled "Flanking sound transmission through lightweight framed double leaf walls". IR-754 is another good paper on flanking. In a nut shell: Unless you deal with the problem of preventing sound from getting into your floor, and therefor into your building structure, you will not be able to produce good isolation. I also noticed that you asked pretty much the same question twice before, back in 2013, and got the same answers then that you are getting now. The laws of physics have not changed in the last 2 1/2 years, :) ... so light-weight timber-framed fully-coupled floor still work the same way they did back then, and the results will still be the same. - Stuart -

OK, maybe I am interpreting your information incorrectly. Are you telling me that I should consider floating the floor upstairs? I was under the impression that floating a floor on a framed subfloor was completely worthless. Am I wrong? I understand the floor drumhead scenario. It would be my goal to somewhat overbuild the subfloor structurally to limit the amount of flex or drumhead movement. I could build a garage inside of a garage but that would probably be a waste of time since the second story floor will always resonate. If I were to build a room inside of a room upstairs, what would be the best reduction in noise outside I could hope to get? Thanks Stuart, for answering my questions. I know that you guys strive for perfection and I’m sure it’s frustrating when giving advice to someone who is not.

Are you telling me that I should consider floating the floor upstairs?

Not float it in the conventional sense, but you can isolate it to a certain extent, with respect to impact noise, by using the "drum riser" principle. That gives you a decent surface to use as a floor, and it is partially damped. It's not as good as a true floated floor, of course, but it works fairly well for impact noise.

If I were to build a room inside of a room upstairs, what would be the best reduction in noise outside I could hope to get?

You could probably expect in the region of 40 dB of isolation, maybe a bit more, if it is built carefully. - Stuart -

Soundman2020 wrote:

Are you telling me that I should consider floating the floor upstairs?

Not float it in the conventional sense, but you can isolate it to a certain extent, with respect to impact noise, by using the "drum riser" principle. That gives you a decent surface to use as a floor, and it is partially damped. It's not as good as a true floated floor, of course, but it works fairly well for impact noise.

Does this mean that he could (or that "one" could) use the "drum riser" principle for an entire floor? Meaning insulation such as Rockwool under a couple sheets of thick plywood (or MDF, OSB, etc)? Would this be suitable to build heavy walls and a ceiling on top of? I'm considering this idea for a small iso booth but I'll create my own thread for that and keep this one on track with the original poster's situation. Not trying to hijack! :D

Does this mean that he could (or that "one" could) use the "drum riser" principle for an entire floor? Meaning insulation such as Rockwool under a couple sheets of thick plywood (or MDF, OSB, etc)? Would this be suitable to build heavy walls and a ceiling on top of?

For the FLOOR ALONE, yes. You can do that. But NOT if you want to put walls and ceiling on it. That probably wouldn't pass code in any case, but it also wouldn't work to well. I guess I should have made it clear that I was talking only about the final floor, placed within the confines of the final inner-leaf walls, and not supporting them. In other words, after the entire room is completely built, you build the floor by putting down your OC-703 or whatever, then your plywood/MDF/OSB/drywall/MLV/lead sheeting/steel plate/whatever sandwich, but making sure that it does not touch the walls! Leave a small gap all around the edges, and fill that with backer rod and caulk. It's important to understand that such a floor is not properly floated, and won't give you anywhere near the amount of isolation that a proper floated floor does, but it does have a very nice attenuating effect on impact noise and low frequency vibration. But do check your local building code, to make sure it is allowable to do that. It might not be in some places. - Stuart -

Thanks Stuart. That is something I've been wondering about for a while.