What is the best way to install insulation in between the floor joists to deaden the sounds of the upstairs when finishing a basement? Would one want the insulation (bats) at the bottom of the joists so they would be touching the drywall ceiling and leaving an airspace at the top or would installing the insulation at the top so they were touching the bottom of the floor provide more quiet? This is assuming that the insulation is smaller than the floor joists.
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Replies
If it was my house I would insulate between the floor joist and hold the drywall off the bottom of the joists. My drywaller said there is a channel that mounts to the bottom of the joists that has a channel that holds the drywall down. You might want to ask a drywall company to see what they have done. I have also heard of using a "sound board" between the drywall and the bottom of the floor joists.
The home theatre sub-woofer shakes the whole house. I am always in trouble for having the volume to high during those shoot'em up scenes
Google acoustic treatment materials. Also, check out http://www.acousticalsolutions.com, http://www.acousticsfirst.com, call acoustic supply dealers near you (if there's any major building going on, there will be at least one place) and some of the better audio/video magazines. There are products that come in a flexible sheet with foam on one side, rigid materials, spray/brush/roll on and the metal channels that your drywaller mentioned. If you want to keep low frequencies from passing through, you need to isolate the two spaces. If it's middle and high frequencies, the rigid, sheet and spray/brush/roll on types will help. Low frequencies go farther (lose less energy) since they're actually vibrating the structure. Highs and mids are moving the air, which is easier to dampen since air can be compressed. The channels for the drywall work like a big pane of glass that you can see vibrating when a truck or train goes past. The moving pane, by being made to move, is out of phase(synch) with the source of the vibration and this is a classic case of "For every action, there is an equal and opposite reaction).
"I cut this piece four times and it's still too short."
Thanks, I see the logic behind having something to stop the transfer of sound through the solid materials but, it seems as if insulation does make a pretty big improvement without breaking the bank. If the insulation is not as thick as the depth of the joists (8-9" for joists and only 3-1/2" for insulation) is it more effective to put the insulation at the top of the joists (touching the bottom of the floor) or at the bottom of the joist space (touching the drywall?)
The sooner you break the transmission of sound, the better. If you install fiberglass between the joists then add a lighter weight material like the old Celotex sheathing (the brown stuff with no real strength) before the drywall, you won't transmit as much to the joists. If you use the channels, you'll stop even more from getting through. Low frequencies are really hard to stop. You won't reduce the bass unless you can decouple the two spaces.
"I cut this piece four times and it's still too short."
fiberglass insulation will attenuate higher frequencies by a few dB, but not alot. It's so cheap, what's the point of only putting up 3.5" thick insulation? Fill the whole joist bay; the labor's the same.
For lower frequencies, you need mass and/or isolation. Two layers of drywall, or resilient channel ( http://www.jm.com/insulation/faqs/996.htm ), will help. Two layers with the channel inbetween will help alot.
Oh, and every ceiling penetration must be sealed against air movement, or they will largely negate any other sound-blocking measures.
This is a common topic of discussion on home theater forums; do a Google search.
Who ever said anything about 3-1/2"? Actually, fiberglass attenuates mids and highs. No highs are going to get past the drywall unless there are big leaks and since the next barrier is subfloor, it's a moot point. If someone did a frequency analysis above the basement noise source, they would see that it's all bass and midbass getting through. The goal here is to do this inexpensively. That said, I wouldn't expect miracles on a budget, but you can block a lot of sound from getting through. The bass and midbass are the hardest to block.I do home theater and have worked in audio for almost 30 years. One dealer I worked for had such bad problems with noise from the overhead heating unit in the mall (right over the high-end room. Great planning by the owners, eh?) and got it to the point that the rumble was no longer an issue. That one, however, was with a suspended ceiling where I could add fiberglass batts and a second layer of mineral ceiling tiles after I had the maintenance crew reduce the speed of the blower. I also treated the home theater room, which had a new (at the time) system called Frox which retailed at about $100K. The walls were flat, parallel and too close together to have anything resembling good sound without being treated.
"I cut this piece four times and it's still too short."
Who ever said anything about 3-1/2"?
Pkghia did (the orginal poster).
You're right. It was pretty early on in the discussion.
"I cut this piece four times and it's still too short."
Top or bottom won't matter in terms of decible transmission.
I've never noticed any apreciable difference by hanging the drywall on metal channels.
Weight is the only thing that seems to work. Seal off any holes between the basement and the upper floor, holes aroun pipes and wiring can transmit alot of sound. Pack in as much insulation as you can. Double drywall the ceiling. Enjoy.
All this talk about air spaces is HS. The joists will transmit the sound, Packed insulation stops them from vibrating. The floor above will act like the top of a guitar, double drywall won't.
The sheathing I was talking about is for reducing the direct connection from the drywall to the joists. The sheathing won't transfer the sound as well as the drywall will. Between that and double drywall, there may not be a huge difference, but it also depends on what frequencies are causing trouble and how you measure it, along with who is upstairs to hear it. Everyone's hearing is different. Dbl drywall does a good job, though. The joists will transmit sound if they're directly connected to the floor and ceiling. The packed insulation dampens the sound getting into the joist space but not the structure borne sound. higher mass makes a difference because it takes more energy to move it. Just a matter of how much you want to get rid of and what you're willing to go through to do it.The air space isn't HS. It's a lot easier to stop sound in air than when it travels through a solid material. Once you create an air space, you can pack the insulation in to quiet it even more."I cut this piece four times and it's still too short."
Edited 11/26/2004 8:57 pm ET by highfigh
Check out the website http://www.soundsense.com They have a couple of products that kill sound transmission and can be used for ceilings or walls. I was provided with a packet of information about this East Hampton, New York based company from the local lumberyard, also in East Hampton. The company deals with a lot of very expensive home theater installations, so I bet it works like a charm. The literature contains comparisons to numerous different configurations of sheetrock, insulation, hat channel, all designed to stop the transmission of noise, and all not as affective as the "noiseout " product offered at soundsense. Good luck Doug
Thanks for all the help. Would it be ridiculous to put some kind of weatherstripping (like dense rubber foam) between the bottoms of the joists and the drywall? I looked at the products offered by soundsense and while it is probably the way to go for a full blown home theater, I am looking for something inexpensive to separate common house noise from one floor to the other.
To keep it inexpensive, that probably won't help much. Better to insulate with lots of fiberglass between the joists. If you can, double 1/2" drywall will help, too. If you plan to wire home theater or anything like that, either do it now and include a way to add wiring later or leave some access panels.
"I cut this piece four times and it's still too short."
Funny you should mention the foam on the joists idea! I just remembered seeing a product in either Fine Home Building or Journal of Light Construction that was just that. The ad showed a guy rolling the foam, which was sticky on one side, onto the top of joists before laying the decking. I'm sure it would work on the underside of the joists also. The idea being to stop vibration through solid wood. I think they even have a tool that allows the installer to stand while applying the strips. I never wanted to use it for floors because I like to glue the ply down tight to avoid squeaks and strengthen the floor, but I think it would work great for the ceiling. If I can find it I'll post it. Doug