wall-ceiling

[LDQ]

Hi all,

I have some questions and concerns regarding my ceiling and wall plan. Just so you know…the walls would be resting on a floating floor. Since pictures explain better than words...check the attached drawing for detail.

1. Which is the correct way to joint the wall with the ceiling. Option A or B? If B is the correct way then….do I need to put some kind of rubber material at the joint or it isn’t necessary.

2. Can the resilient channel hold 3 layers as it is in the drawing? If yes…. can I put a screw through the 3 layers or how is the correct way to do it.

3. Do I have too many layers on my ceiling (Overkill) or how can I have same of better isolation with less layers.

4. How do I Attached my 4” Mineral Wool Insulation acoustic Treatment to the ceiling?

Regards,

Luis.

 

[LDQ]

Bump...

Hummm....50 hits and no one has nothing to say.... I can use a little help here.

Thanks,

Luis.

 

[Michael Jones]

Option "A" is going to crush everything.

Use Option "B", but put a rubber pad between the ceiling joist, and the top plate of the wall.
That way, your wall is acoustically disconnected from the ceiling.

 

[longsoughtfor]

Luis - is the ceiling in "A" really the floor joists for your first floor or are you making a new ceiling?

I sort of did A because the joists are supported by the concrete walls of my basement. I brought the walls up to the particle board/MDF and the sheetrock of the ceiling butts the wall but is isolated from the MDF.

Kevin.

 

[LDQ]

Option "A" is going to crush everything.

Use Option "B", but put a rubber pad between the ceiling joist, and the top plate of the wall.
That way, your wall is acoustically disconnected from the ceiling.

Michael,

How does the wall get secured to the ceiling....only pressure between ceiling joist- rubber padd- and top plate of the wall ?..... Or do you need to put some kind of glue to hold it together. Since we are trying to isolate wall from ceiling I guess screws between these 2 are a NO NO.

Let me know.

Thanks for your response by the way.

Cheers,

Luis.

 

[Guernica]

Hi Ldq,
First of all, I am a drywall contractor... not an acoustical engineer, so my advice pertains to construction experience and not engineering knowledge.
Im assuming a few things: that the ceiling joists are the floor joists of a second story, and that the framing is wood.
The ceiling/wall assembly, as i have done it is fairly simple. The wall framing is attached directly to the joists. The suggestion re: using a rubber pad between the wall and joists is a good one. The layer of resillient channel that you have drawn goes between the 1st layer of drywall and the next material, not against the stud. It is there to provide an air-space between the 2 layers. As im sure you know, the res. channel is applied perpendiculare to the wood joists. Ive never heard of using mdf for the next layer, but that doesnt mean it isnt done. I just dont understand the necessity for the extra weight. If i were you, I would apply 2 layers of 5/8" drywall directly to the joists (the first w/ 1-1/4 screws, the second w/ 2"), then the resillient, then one more layer of 5/8"dw. Whatever you do, dont hang two layers of material from the res. channel... ....Its not rated for it. I wouldnt waste the time and material w/ what you have between the joists, the sound will travel through the joists more than the airspace between them. The drawing suggests that the joists are 2x10. If so use r-30 ins instead of the r-13.


hope this helps, g

 

[knightfly]

There are those who design acoustic spaces that will strongly disagree with Guernica's statement, "The layer of resillient channel that you have drawn goes between the 1st layer of drywall and the next material, not against the stud. It is there to provide an air-space between the 2 layers. " -

In partitions for sound proofing, the terms "mass" and "spring" are used to describe panelling and air space, respectively. Air is considered a spring, and a relatively stiff one. If you build a partition that has 3 layers of mass separated by two layers of air, that is considered a "triple leaf" construction, and will actually have LESS sound attenuation than the same amount of mass distributed in only TWO layers.

The reason for using dissimilar materials for successive layers in a single "leaf", or layer of mass, is to put yet another change of resonance and slight diffraction angle change in the path of the sound that you're trying to contain, making it harder for the sound to get through. So, the MDF sandwiched between dry wall is good for that.

As far as the RC not being rated for multiple layers, that would depend on the RC and the method of construction. Generally you can put two layers of drywall on RC, but should place the RC on closer centers (16" instead of 24") - for a ceiling using 3 layers, I'd place the RC on 12" centers and make sure to use large screws with big heads when fastening the RC to the ceiling joists. When fastening the panels to the RC, make reference marks where the joists are(near the top of the wall), that can be seen AFTER the panels are in place, so you NEVER put screws thru the RC where it crosses the joists. This will preclude "shorting out" the RC with a screw. Also, mark (at the top of the wall) where each RC is positioned, making sure you install it in a perfectly straight line, so you can find it with the screws.

I'd use successively longer screws for each layer, and stagger them each layer, using a tight pattern (about every 6", each layer) using your wall marks to locate chalk lines. By staggering the screws for each layer, you will keep the multiple layers from tending to vibrate independently. Some construction adhesive between layers wouldn't hurt either, for the same reason. You want the multiple layers to act as ONE layer ultimately.

I would also orient the middle layer of MDF at 90 degrees to the inner and outer, so you have no continuous cracks for sound to bleed through.

Your drawing doesn't mention what the wall construction is - if it's two back-to-back steel stud partitions with double drywall on the inside of the inner, and on the outside of the outer frame, then by all means use the 3 layer ceiling with all the other construction you show. If it's less than that for walls, your ceiling may just BE overkill. Remember the "weakest link" syndrome, and don't waste time/money on one facet unless all the rest is equal... Steve

 

[Michael Jones]

There will ALWAYS be a connection between structural members. "Complete" isolation in construction is simply not possible. Some sacrifice of acoustic islolation, for structural integrity will, by necessity, take place. But there ARE things we can do to MINIMIZE that structural link WITHOUT sacrificing structural integrity.
RC channel, is one example.

There are a variety of methods to secure your floor/ceiling joists to your walls. Be sure to check with your local building codes to see which ones are acceptable.

That said, here's what I would do:

You'll need some sort of bracket to make the connection.
Put the piece of rubber on top of the top plate of the wall.
Take the bracket shown, and nail or screw it to the top plate of your wall through the rubber. Take anothe piece of rubber, and place it on top of the bracket.
Place your joist on top of that rubber. Secure the joist to the vertical member of the bracket. The only real link to the wall now, is the 2 screws or nails holding down the bracket.
I would use two brackets, one on each side, offset on top of the top plate. Think of them as bookends, with the joist being the books. Offset the horizontal members of the bracket so they're not touching each other.

Construct ceiling as shown in option "B".

Make sense??
Clear as mud?

 

[LDQ]

Your drawing doesn't mention what the wall construction is - if it's two back-to-back steel stud partitions with double drywall on the inside of the inner, and on the outside of the outer frame, then by all means use the 3 layer ceiling with all the other construction you show. If it's less than that for walls, your ceiling may just BE overkill. Remember the "weakest link" syndrome, and don't waste time/money on one facet unless all the rest is equal... Steve

Thanks Steve,

You just cleared up a lot of doubts I had in my mind.

All my walls are John's inside out design. 2x4 studs with 4" rockwool in the cavity... 2 layers of 5/8" sheetrock and 3 1/2" R13 insulation on the outer side. The walls of my basement are concrete.

Do you think the 2 layers between the joists above the r13 insulation are nesesary?

Is it alright to just seal the last layer of sheetrock witht the wall or do I need to seal inside the joist cavities.

Thanks again,

Cheers.

Luis.

 

[Jeff_D]

Mike- you MUST be a design professional- "clear as mud"- classic designer jargon- i hear that every day!

 

[Michael Jones]

Mike- you MUST be a design professional- "clear as mud"- classic designer jargon- i hear that every day!

I like that saying!
Yeah, I'm a civil engineer with a background in structural.

 

[knightfly]

Luis, sorry for the delay in getting back to you - your question - "Do you think the 2 layers between the joists above the r13 insulation are nesesary?

Is it alright to just seal the last layer of sheetrock witht the wall or do I need to seal inside the joist cavities."

The two layers above the R13 will add mass to the first "leaf" of your ceiling. If you expect ANY footfall noises from above, or if you plan on recording live drums while someone upstairs is trying to read or watch a TV program, then YES. The more mass involved, the better.

As to sealing, you can't EVER use too much caulk. (Well, you could but you'd know by the fact of your shoes sticking to the floor)

Just a general rule - when soundproofing, ask yourself if you would caulk that joint if it were the bottom of a boat you intended to sail around the world - if the answer is yes, then the answer is yes.

Think of this: If you put up three layers of sheet rock and only caulk ONE layer, then you just paid for 3 layers of sheet rock and got the benefit of (slightly more than) ONE. Buy more caulk. (Either the non-hardening silicone, or non-hardening Butyl are fine)

 

[LDQ]

As to sealing, you can't EVER use too much caulk. (Well, you could but you'd know by the fact of your shoes sticking to the floor)

)

Hi Steve,

The problem I have is that the first layer of wood that goes on the floor joists is not a 4x8 sheet of plywood but a lot of 8"x8' long slats of wood and they are spaced about 1/2" apart leaving a gap between them. On top of that layer I have hardwood floor. Looking at it from the bottom I can see the gaps between each of the slats... A lot of them....so If I caulk all those gaps in my entire basement...I think I will go broke plus it will take me forever to finish sealing everything . Is there something other than caulking that I could use to seal those gaps. Something that would cover more surface area.

I have a picture of it but I can't post it here is to big...40M let me know maybe I can email it to you.


Regards,

Luis.