Wall Construction - Insulation Installed wrong

This website has been very helpful for the design and construction of my studio. I have recently completed the build after years of research and multiple designs. Unfortunately, I have discovered that my builder installed the insulation in my double walls design wrong. The original design was a double wall with a 2"air gap (see image below) After the drywall went on I discovered that the insulation on each side of the double walls were compressed together where the 2" air gap was suppose to be, leaving a 1" air gap on the sides next to the drywall. (see image below) I have a concerns that the STC and acoustics are going to be effect by this improper construction. How do you think this will effect both the STC and acoustics in the rooms? Do you think I should pull the drywall off and fix the issue? Thanks in advance, Greg

Greg, I wouldn't worry too much about that. It's not a big deal. The position of the insulation has only a very slight effect on overall isolation, nothing to be worried about. The purpose of the insulation is to damp resonance in the cavity, and it will still do that in the middle of the cavity, just as well as it would if it were in the other location. - Stuart -

+1 with what Stuart said.

Actually, looking closer at your diagram, it does say "Insulation compressed together". Does that mean that they forced the insulation into the tiny gap between the studs on the outer leaf and inner leaf? If so, then you have a problem. Compressing 6 inches of insulation into a two inch gap between studs is way more than enough to create a flanking path. In other words, if he just laid the batts into the stud bays but did not force them in sideways between the two sets of studs, then you are probably OK. But if he did do any "compressing", and the compressed insulation is touching both sets of framing, then you do have a problem. If you have any doubts at all, then get your builder to take off the drywall on one side, and correct the problem, AT HIS OWN EXPENSE, not yours. He screwed up by not following your very clear instructions, so to my way of thinking, it is his responsibility to fix it and absorb the cost of doing so. Of course, he cannot re-use the same drywall: it will have to be junked and replaced with new stuff,and new Green Glue. That's going to hurt his pocket... - Stuart -

Hmmm...Looks like they just shifted the air cavity location from the center to the drywall faces. As you pointed out this wouldn't affect anything unless the insulation were compressed.

Hmmm...Looks like they just shifted the air cavity location from the center to the drywall faces. As you pointed out this wouldn't affect anything unless the insulation were compressed

That's the way I read it. It would be good to know how much (if any) the insulation is compressed. Thanks for chiming in, Ted! :) Much appreciated. - Stuart -

The Insulation was compressed together between the walls. This was done by stapling the insulation (in the center of the studs) - which ended up compressing the insulation from one side up against the other.

I can say we never formally tested double stud walls with the insulation purposefully compressed. Perhaps that diagram should read "Insulation Contacting." Having said that, I don't understand how you described the insulation being compressed.

"After the drywall went on I discovered that the insulation on each side of the double walls were compressed together where the 2" air gap was suppose to be, leaving a 1" air gap on the sides next to the drywall. (see image below)" How do you see this? I mean...how is it that you can look down into a double wall assembly and not take a picture that would be far better than a sketch...just saying... You have to compress insulation to where the parts become hard (or near hard) due to the compression. To allow them to "touch" which seems to be this case is not going to harm you at all. If in the future, you have more flanges of your batt insulation to install, install the flanges on the top side of the stud rather than to the inside, it makes the placement better, the air barrier is tighter and you have a better overall wall assembly.