Insulation In Double Wall Construction

[CPL]

Hi,

In my backyard I am building a practice studio which has double-wall 2x4 stud construction with a 4" airgap. My question is insulation. I am going to put insulation in both walls. Should I use 3.5" insulation in each wall to maintain the air gap, or is it better to use 6" insulation in each wall. Using 6" insulation means that the 2 layers of installation would be touching. Would that defeat the purpose of the airgap?

My main concern is not annoying the neighbors. I am not as much concerned about the sound inside, or outside sound getting inside.

Thanks,

Craig

 

[knightfly]

Can you either post a drawing, or describe your wall structure layer by layer, from outside to in?

 

[CPL]

Hi,

From outside in -

1/2" Plywood siding
5/8" gypsum
5/8" gypsum
2x4 wood stud wall
4" air gap
2x4 wood stud wall
5/8" gypsum
5/8" gypsum

Craig

 

[Terarin]

You should fill in the gap with insulation unless you can make it airtight gap to lead to the warmest/cooling in your filling, because your actually then creating what is known as a vacuum, dead space, in there if it is completely sealed. But this is no way of doing a house or shed right now unless you sheetmetal it and completely seal it off (warmest/coolest at whatever temperature you have it set for). But it you do decide on putting insulation in most recommended I would try building each wall as a individual and putting another seperate piece down inbetween then but I would go with the widest stuff I can findif your going to do that.

When I build double layered wll I tightly combine the two wall and off axis the whole thing so there are never two alike, warmest possible in combination, drop the heating cost to $30 a month. With your you only gain like maybe $5 to $10 more it the cost which is used up for each things your put in there so you'll only see a profit from it after 2 years maybe 3 years if it is small. That is a greatly increase wall for temperature wise in keeping your heat/cool air inside and the outside air out of your house

 

[phaqu]

On my last place I built, I used a 1" air space in between the inner and outside walls. But I also sheetrocked the backside of the inner wall,it wasnt easy,but it helped . To get and airtight seal on the floor, run a bead of glue on the floor where the wall will be placed. One trick I tried was after the first layer of sheetrock, put a layer of rubber or pond liner ( about 1/16th of an inch thick) up before you put your last layer of rock down.I used a tile glue that came in a bucket, and spread it with a glue trowel.Aurolex calls it sound block, (and charges $3.50/square foot). The pond liner was 35 cents a square foot and came pretty close to doing the same thing. . Run your first layer of rock up and down, mud and tape each seam and joint, then the next, run it horizontal,again mud and tape( if this is your final layer, you might have to put a few coats on, sanding in between each one for a nice finish). That keeps the seams from laying on top of one another.With insulation, the fluffier, the better. Dont try to smash R-30 in a 2x4 wall.It doesnt work as well. And a can of Great Stuff will do wonders with hard to reach and outside air gaps. One more thing I tried to do,if you have the space, is to keep the dimensions of the room non divisible with each other. Like,..you dont want a 12x20x8. Try for a 13x21x8.5. That will keep standing echoes from occuring. And non parallel wall are good for that to. Ive done this a few times and learned a trick or two along the way.

 

[RICK FITZPATRICK]

"ahem"...this thread is three years old...but don't feel bad, I did the same thing two days ago But I do want to add a few things regardless, for those who will still read this thread. Here is the first question.

In my backyard I am building a practice studio which has double-wall 2x4 stud construction with a 4" airgap. My question is insulation. I am going to put insulation in both walls. Should I use 3.5" insulation in each wall to maintain the air gap, or is it better to use 6" insulation in each wall. Using 6" insulation means that the 2 layers of installation would be touching. Would that defeat the purpose of the airgap?

This is a peculiar situation Take a look at this.

As you can see, its very clear, that a TWO LEAF-MASS AIR MASS assembly performs much better than either a THREE LEAF or FOUR LEAF system, especially when ONE LEAF is decoupled from the other by either Resiliant channel, staggered stud, or double walls. However, in all cases, this presents a conundrum, which may or may not apply to your particular local codes, although I think most American metropolitan and even rural Building codes are adapted from the UBC(Uniform Building Code). Now I'm no expert on the UBC by any stretch of the imagination, but common sense tells me residential stud wall framing requires a FIRE STOP, which is simply a wood spacer, nailed between each pair of studs approximately 48" from the floor. Since this spacer is captured between the studs, and the drywall on each side or exterior sheithing, it places a barrier to a fire that starts in a lower area of a wall or floor. Hence the term fire stop.
However, when you build any type of studio isolation wall, especially double wall scenarios, the purpose of "decoupling" one framing from the other requires that NO rigid connection exists between each framing assembly. This means, there is NO way to physically place a "captured" fire block in the airgap that touches BOTH LEAFS. From previous threads posted here in the past, it has become clear that INSPECTORS, who sign off on construction that has been built with PERMITS, have REQUIRED a rigid stop placed in such a way where the airgap is blocked to prevent the spread of fire. It was just this type of problem that prompted a little research.

What I found was that some municipalities had a code that solved this problem with double walls, by filling the airgap from leaf to leaf, at least 24" high with insulation to act as a fire stop. As far as I understand it, as far as sound is concerned, this actually improves the transmission loss of the assembly. I wont't go into to it though. But there are some other "net fact" issues in the last two posts that need some clarity and outright correction.

You should fill in the gap with insulation unless you can make it airtight gap to lead to the warmest/cooling in your filling, because your actually then creating what is known as a vacuum, dead space, in there if it is completely sealed.

I'm sorry, but it is impossible to create a VACUME in a framed wall airgap. A hermetically sealed airgap yes, but vacume, no. Dead air space is correct. But you lost me on the... "unless you can make it airtight gap to lead to the warmest/cooling in your filling" part

Same with this..."When I build double layered wll I tightly combine the two wall and off axis the whole thing so there are never two alike, warmest possible in combination,"..... Can you clarify that?

Next...

But I also sheetrocked the backside of the inner wall,it wasnt easy,but it helped

According to the TESTED ASSMBLYS above, it appears you have built either a three leaf, or four leaf assembly. Too bad you didn't see this first.. You could have saved a hassle, time and money on a BETTER assembly.

. One more thing I tried to do,if you have the space, is to keep the dimensions of the room non divisible with each other. Like,..you dont want a 12x20x8. Try for a 13x21x8.5. That will keep standing echoes from occuring.

I believe this is incorrect. There is no such thing as "STANDING ECHO". Thats an oxymoron. An ECHO is a TRAVELING WAVE, not standing....otherwise..well, how would it be an echo if it was "standing"? It is a Standing Wave, which can form between ANY two parallel surfaces, regardles of the length/hieght dimensions/ratio. I believe the dimension multiples, have to do with modal frequency distribution.

Ive done this a few times and learned a trick or two along the way.

Hmmm, I bet you did. The trick is figuring out if they worked better than TESTED assemblys. If so, maybe you should contact the experts.
fitZ

 

[phaqu]

A "standing echo" is a term dealing with frequency multiplications where a specific wave bounces and doubles itself.intensifing each time (might be an outdated term?). The reasons for the non divisable measurements doesnt totally eliminate them, just keeps the number of frequencies that will down to a minimum. Might be the same thing your talking about.Id have to dig up the formulas somewhere. On the constuction of the rock on the back side of the wall, the outer wall was concrete with a fire block/sound attenuation insulation on it (very nasty stuff) covered with carpet padding. Im not sure what the differance would have been if I would have left it open, but I also used a brute force density type of soundproofing on the inside of the inner wall. Way more that just 2 layers of 5/8 rock(but I wasnt going to go into depth with it). I also used the rubber on any wood to wood, rock to wood contacts to try to keep vibrations from transfering. I wasnt throwing anything up out of the blue, Ive read up on a lot of soundproofing techniques and material properties (absorbtion, diffusion and transference). Some seemed to contradict one another. Different people,different tests,different ideas, hell I dont know. Either way,... it worked well for me. And this thread is 3 years old.