Help with wall design

Hi there, With my budget I've got: outer layer - 6mm cement sheet Pine studs Acoustic insulation (pressed against outer wall) furring channel (15mm) rubber strip against furring channel to seperate plaster from furring. 13mm acoustic plaster My idea was to create an air gap between the plaster and the studs so I though furring channel and then also put rubber strips between the plaster and the furring channel to minimise vibrations. But..... I've been reading and got confused with "insulation against plaster to dampen" & "furring channel won't help sound proofing" Have I made the right decision? What can I change before I start construction? Structure is on a slab which will have carpet and a pitched roof/cathedral ceiling from 2.7 walls going up at 30 degrees. 12mm plate glass windows.

It would help if you could describe completely what it is you are trying to accomplish! With what you have said so far, it is kind of like saying "Hi there. I have a piece of string, and I want to know if it long enough.".... :) Long enough for what? What is it you are trying to do? About the only comments I can add is that the furring channel probably wont help, and neither will the rubber strips, the 6mm cement board is probably too thin, the 13mm drywall is definitely too thin, and the "acoustic insulation pressed against outer wall" probably isn't doing anything for you either. It sounds like you are trying to build an MSM wall, but that just isn't the way to do it. If you want good isolation, what you should have is MSM, meaning "Mass" (such as 10mm cement board or 16mm drywall) a large "Spring" (meaning an air gap of at least 10 cm, filled with fiberglass or mineral wool insulation), and more "Mass" (meaning at least one layer of 16mm drywall. The outer "mass" and inner "mass" should be mounted on separate stud frames, or at least on staggered studs, or perhaps on resilient channel (which is not the same as furring channel or hat channel). Each "Mass" must be totally sealed airtight. the ceiling must be done in the same way: MSM. Also: carpet on the floor is a bad idea, as it is frequency-selective: It absorbs highs well, mids to a lesser extent, but does nothing at all to lows, so your room will end up sound boomy, and ugly. The 12mm plate glass windows are also going to be a problem, probably. But with more detail of what you plan to do, and a good SketchUp model, it would be easier to help. - Stuart -

Thanks for your reply. I'm really just trying to build a wall that has better acoustic properties than your average shed wall with a tight budget. hmmmm...... here are some pictures - I'm trying to keep the walls thin so I don't take up so much floor space. Really trying to compensate a little bit of noise reduction from outside sources when I'm recording and concentrating (dogs, kids etc) and also at night when I'm composing, minimal bass and rocket 5" speakers. Maybe I need an extra layer of plaster? instead of the 15mm gap with furring channel?

Soundman2020 wrote:

If you want good isolation, what you should have is MSM, meaning "Mass" (such as 10mm cement board or 16mm drywall) a large "Spring" (meaning an air gap of at least 10 cm, filled with fiberglass or mineral wool insulation), and more "Mass" (meaning at least one layer of 16mm drywall. The outer "mass" and inner "mass" should be mounted on separate stud frames, or at least on staggered studs, or perhaps on resilient channel (which is not the same as furring channel or hat channel). Each "Mass" must be totally sealed airtight. the ceiling must be done in the same way: MSM. Also: carpet on the floor is a bad idea, as it is frequency-selective: It absorbs highs well, mids to a lesser extent, but does nothing at all to lows, so your room will end up sound boomy, and ugly. The 12mm plate glass windows are also going to be a problem, probably.

We thought we would make our own home made version of resilliant channel by using rubber offcuts to mount both the furring channel onto stud work and also plaster onto furring channel. Carpet bad idea? what should I do on the floor? Double glaze was too expensive and the 12mm double panel plate glass we had already from an office building. I guess the real concern for me is that we wasted money on the furring channel and its a 15mm gap we could gain on all walls if we didn't use it or should we just add another 10mm plaster layer with green glue (cost?). How should we lay the insulation?

I'm trying to keep the walls thin so I don't take up so much floor space.

Well, there are two major components in one of the key equations that determines how your wall isolates. One of those components is "mass", the other is "thickness" (or more correctly, the size of the air gap). So, if you need to make your wall thinner, then you have to increase the mass. There are no short-cuts around the laws of physics, and no magical materials that defy them. Right now you are specifying 6mm cement board for the outer leaf. Making that 10mm costs you nothing in terms of interior space. In fact, putting two layers on costs you nothing. Or even a layer of plywood / OSB underneath. All of those will increase your mass substantially. And make sure that it is sealed airtight. The, for your inner leaf: You already have the stud frame in place, according to the photos, so it's too late to change that to staggered studs. And you don't have the space to put up another frame next to it. So your only remaining choice is resilient channel (RC). This is NOT hat channel, and it is NOT furring channel. It is a specially designed metal channel that is engineered to provide acoustic decoupling. It is the only thing that works, and you cannot substitute ordinary hat channel, or anything else. The purpose is to acoustically decouple your inner leaf from the outer leaf. Put a layer of 16mm drywall on the RC, or if you need better isolation, then make it 2 layers. And fill the gap between the inner leaf and outer leaf with fiberglass insulation. Do the same for the ceiling: RC on the joists, and a layer (or two) of 16mm drywall, with insulation in the air gap. Bingo! Good isolation. But you will also need to isolate your windows and doors, and you have a major issue with that "attic thing" at the top of the ladder. That is going to take some extra treating, or sound will be leaking out that way. - Stuart -

This is the idea (the cheap version of resilient channel that apparently wont work :( I guess I was more thinking of making a gap between studs and plaster. Should I put insulation to the channel or all the way to the plaster? Plaster Stud adhesive Rubber 15mm channel Rubber Stud

the cheap version of resilient channel that apparently wont work

Correct: It won't work. It does not decouple the drywall from the framing, so it will not work, period. It probably also violates building code, and will not pass inspection... There is one other way of getting the same result: using RSIC clips plus hat channel. That will give you about the same result as proper RC. And will probably cost you something similar.

Plaster Stud adhesive Rubber 15mm channel Rubber Stud

Sorry, but that's just not going to accomplish anything useful, except to waste a lot of your time and some of your money.

Should I put insulation to the channel or all the way to the plaster?

For maximum isolation, fill the entire air gap between outer leaf and inner leaf with normal pink fluffy fiberglass insulation. Of course, if you continue with your original plan and do not do it correctly as a proper MSM wall, then you might as well forget the insulation too, since it wont make much difference, with or without. Once again, it would just waste money. Unfortunately, there are no shortcuts or miracle construction materials. All materials are subject to the exact same laws of physics, and there simply is no way around that. Either you do things the right way, using the laws of physics to help you, or you wont get decent isolation. What you want to achieve isn't that hard to do, especially since you don't need fantastic isolation, and it only needs a solid scientific approach, which is what I outlined for you above. - Stuart -