Low Basement Ceiling

My basement ceiling is about 6'6 and I don't want to lose any more ceiling height by attaching drywall to it and I would also like it to act as a broadband absorber at the same time. The house was built around 50 years ago. The joists are 7" deep and spaced around 22" apart. Someone recommended I screw drywall to the subfloor between the joists, gluing it and ceiling it off. A layer of quietrock would then be caulked and screwed to the drywall. After that rockwool would be stuffed in between the rest of the joist and covered with fabric. Wouldn't this make a single leaf system though? I'm wondering if it would be far more effective to have a space between the layer of drywall and quietrock about a half an inch instead? I know there's a few posts about adding drywall in between joists on here but they all seemed to have drywall put over the joists as well. If anyone could help me it'd be greatly appreciated 8)

Wouldn't this make a single leaf system though?

Yes.

I'm wondering if it would be far more effective to have a space between the layer of drywall and quietrock about a half an inch instead?

That won't do anything about the joists! They will flank the sound directly to whatever you use as your lowest layer. And a half inch is not enough airspace to be useful: you need at least several inches (four or more). Unfortunately, if you want isolation you are going to have to sacrifice an inch or two of height. You still need to beef up the floor above anyway (just like you said, with a couple of layers of drywall attached to the floor between the joists, then rockwool) but you also need to have a decoupled second leaf underneath that. In such limited space, your best bet is probably to use RC directly on the joists, and hang your drywall from that. Depending on how much isolation you need, one sheet of 5/8 might be enough, but my guess is that you'll need layers two plus a layer of Green Glue in between. However, having said that: Are you absolutely certain that those joists can handle all the extra load? You are talking about adding many hundreds of kilograms of mass to that floor above you. Did you check with a structural engineer to make certain that you actually can do that safely? - Stuart -

The floor joists are going across a span of 10 feet to the beam and it's made of Douglas fur. So it should be able to support 2 layers of drywall no problem. Here's another Idea I have. If I were to have a layer of drywall glued, screwed and crackfilled to the subfloor, and put 4 inches worth of rockwool on top of it. Then mount a layer of quietrock to strapping around 4inches down the joist (glued and caulked) and have it covered with 2" of rockwool so I can have the whole ceiling as a broadband absorber without it taking up headroom. Would that do the trick? Not expecting to get complete isolation. But enough so it's not that loud on the floor above. Here's what it would look like. Thanks a lot for the help. It's greatly appreciated 8) X = Floor Joist W = Rock Wool S = 2x2 stud to hold quietrock = = 5/8" Drywall Q = Quietrock 516 _ = fabric XX============XX XXWWWWWWWWXX XXssWWWWWWssXX XXssWWWWWWssXX XXQQQQQQQQQQQXX XXWWWWWWWWXX XXWWWWWWWWXX _________________

Look at your line of "XX's", going vertically. They directly connect the floor above with your layer of "quietrock". This is called "flanking": So basically all of the rockwool in between is wasted: it does nothing useful, since the sound "flanks" around it, through the joists. So basically, you still only have one leaf, just more massive than before, and with several built in air-pockets.

So it should be able to support 2 layers of drywall no problem.

"Should be able to" isn't good enough. You must check with someone who actually knows what they are talking about with structures, and is qualified to to the anaylsis: You need to check with a structural engineer. And it isn't just supporting 2 layers of drywall: It is supporting the drywall, the "quietrock", the rockwool, the screws, the glue, and the fabric. It all adds up. You don't say how much area you need to treat, my guess is that you are talking at least a thousand kilograms of mass. Do you really think you could drive a car across that floor quite safely? Would you be happy to sit underneath that floor with a car parked on top? I wouldn't. Check with someone who can do the math and confirm in writing that those joists can take an extra few thousand pounds of load without any trouble.

Sistering the joists will get you around that issue. Added expense, no car in basement. :) You may then hang proper treatments. I do agree with Stuart, seek qualified advice before ANY structural work. Ignorance can get you hurt. :cop: W

WayneD Wrote:

Ignorance can get you hurt.

Amen............................ :wink: Lou. 8)

I was just thinking that the quietrock would be more efficient if it wasn't touching the subfloor completly. Have any of you heard of the stuff before? It's supposed to be the equivalent of 8 sheets of drywall. It has a layer of this stuff inside that deadens it.

Your 24 inch center joists are not even up to current code. The extra load on the existing joists may not be an issue...until someone walks on the above floor. Then you have an issue. Quietrock may be a good selection for this specific concern, if you do not mind spending the money. What is it these days $175 a sheet? You should consider installing 16 inch joist layout framing, if you build overhead or even if you do not;) It isn't an area to play with. Enlist a qualified technician to get it up to code for your safety.

I was just thinking that the quietrock would be more efficient if it wasn't touching the subfloor completly

Well, it WILL be touching the subfloor, because the joists are attached to the subfloor, and the quietrock will be attached to the joists. Sound (vibration) will flank trough the joists to the quietrock. Also, do the math: According to their website, the type of quietrock panel that is equivalent to "8 layers of drywal" also weighs in at roughly 31 kg/m2: Add in another 12 kg/m2 for your layer of drywall, and let's say another 4 or 5 kg/m2 for rockwool, screws, glue, fabric, etc. You are getting really close to 50 kg/m2! Yikes! So let's assume that you have a 10 x 5 m area to treat: that means roughly 2,500 kg of extra mass, hanging from those 24in OC, joists? 5,500 pounds? WOW! I was wrong: That's not one car worth of mass: That is TWO cars worth of mass. Would you be happy with two cars parked on top of that floor? Do you think the joists could handle that? Think of it another way: That's the same as putting 32 normal full-grown adults in the room above. . . . OK, more math: You say your joists are 24 inch OC, that's 61cm. Assuming that your 5,500 pounds would be spread over 5 meters of floor width, that means you have two and a half metric tons resting on only 8 joists. So you are asking each joist to support an extra 687 pounds (312 kg), in addition to whatever it is already supporting? That's four additional adults standing on top of each joist . . . No way!! Uhh uh!! Please do not ever invite me down to that studio! Get a structural engineer, and get him to tell you how to fix that floor before you start hanging stuff from it. There is no way it can safely take the load you are planning to hang on it. I can tell you that just from common sense and simple math, and I'm not even a structural engineer! Listen to what xSpace is saying: He knows a bit about construction. If he says your floor is not safe and needs rebuilding, I'd certainly be listening really hard! - Stuart -

It would only 700 pounds Spread over a section 10'x12' for 2 layers. A pool table weighs more. This is in between 2 support beams which are held up with a load bearing wall containing jack posts. It's only costing me $64 a sheet. The 5/8" stuff is something like $104 or something I figured it would reduce the sound more because it would only be touching on the sides and not the middle. Since it's sound dampening then It would absorb it

rossome, could you post an accurate drawing of your space? Include dimensions for size of joists, distance on center, etc. That will really help everyone understand your space. Which is often the most difficult thing to do. W

This is roughly what it looks like. The lines going up and down are the joists which range around 20"-22" on center. 2" wide and 7" deep and span 10 feet till they either hit an 8"x8" beam, load bearing wall or foundation. The little section in the back of the control room is 8'x8' and the live room is 10'x19'

rossome, looking at the drawing and researching the load capacity of joists/lumber the things I have found are; -the joists do more than support the above floor, they contribute to the integrity of the building -it is recommended that you check your local code as it relates to the build you have -get professional advice on the your plans -tributary load functions are the hidden job of joist systems, in other words, they are doing more than they look to be doing -the OC spacing and joist size determine the load carrying ability -a pool table weighs over 1000lbs -dead weight loads, such as a pool table or drywall need to be calculated against the structure to determine if the structure needs beefing or not These are by no means all inclusive. Others may have different insights and thoughts. However, the main theme here is, do the research. Unbalancing the structural load of the building, although not apparent at first, could show up at a later date. This could be in the form of weakening, shifting or something else quite apparent. Your 2x8s seem suspect by design. Please use a trusted professional for advice. Do what they recommend. Then build what you want. Get more than one opinion. And be safe. xSpace has much experience with construction. He has recommended the same things I have said above, in less words. Although the research was good for me. Thanks for sending me in that direction. Also, there are insurance implications (at least in NJ) should you alter a structure without obtaining the proper permitting. Get some help rossome, it will save you much heartache in the long run. W

A structural engineer here in the States will charge you around $100-150 to come and do a DETAILED inspection and give you a nice report. It is money well-spent, and in fact, I would say it is money you MUST spend. Do not take this lightly.