Most the testing you will find for double stud and staggered stud framing are lab tests for walls only. We still have not seen a sound test of any kind for a ceiling with independent joists. However, the concept of decoupling with framing is well established, so there is no reason to assume an independent ceiling joist is not significantly better than a standard fixed joist. The real question is how resilient sound clips compare to double stud walls, staggered stud walls, and independent joists.
Staggered Studs vs. GenieClips
The STC rating of a staggered stud wall with double layer drywall on one side and single layer drywall on the other side is STC 47. The transmission loss in decibels at key low frequency points of 80Hz and 100Hz are 29 and 36. The STC rating of a GenieClip system in the same type of assembly is STC 61. The transmission loss in decibels at key low frequency points of 80Hz and 100Hz are 27 and 33. You can see the GenieClips perform 14 points higher in STC (every five points a doubling effect) and just a few points lower in the lowest frequencies. This performance loss in low frequencies can be made up by adding a third layer of drywall either on the clips or on the other side of the wall. This extra layer will change the 80Hz and 100Hz performance of the GenieClips to 31 and 39 and increase the STC even further to an impressive STC 64 now exceeding the staggered stud wall in performance without taking up additional floor space. The tests referenced were done in the same lab so comparing the two isolation methods is accurate.
Double Stud Walls vs. GenieClips
The STC rating of a double stud wall with double layer drywall on one side and single layer drywall on the other side is STC STC 64. The transmission loss in decibels at key low frequency points of 80Hz and 100Hz are 35 and 40. This is clearly a high rating in low, mid, and high frequencies. The double stud wall will rate 3 STC points higher than the GenieClips in the same assembly and even more significant gains in low frequency performance when comparing head to head with GenieClips in a similar mass assembly. However, adding that additional layer of drywall to the GenieClips or to the other side of the wall will increase the STC to match the performance of the double stud wall and the 80Hz performance within 4 points with the 100Hz performance now just within 1 point.
Independent Joists vs. GenieClips
This is a tough one because there are no tests for independent joists that we can use to compare to the GenieClips. The concept of framing in independent joists, meaning joists that are separate from the structure and used to support the ceiling drywall only, definitely makes sense. It’s not a crazy assembly or gimmicky approach. We expect the performance of this method to be very high and likely similar to what a double stud wall can accomplish, but adjusted for a typical ceiling rating. Since GenieClips with four layers of drywall will rate nearly the same as a double stud wall with three layers of drywall, we believe it is safe to assume that this performance comparison will be comparable in a ceiling assembly.
Lab vs. Field
The testing discussed above was all done in the same lab and not in the field. In doing so, they are only comparing the performance of the isolation method and not the performance of the isolation method in relation to the entire assembly (adjacent walls, floors, ceilings).
Staggered stud walls – The problem you will find with staggered stud walls is while the studs are offset and decoupled, they share the same top plate and bottom plate framing which tie directly into the ceiling joists and sub- floor. This is a major flanking issue. The staggered stud wall is already shown to be an average performer considering the effort in construction, but in field tests it will rate even worse. A staggered stud wall with clips installed is a great idea for increasing low frequency isolation, but a staggered stud wall alone is really overrated.
Double stud walls – In the lab there is no concern over flanking so the results can be misleading. If you use independent joists with double stud walls, then the top plate connection is not a concern. The floor flanking exists whether you have double stud, staggered stud, or a resilient clip system so that issue must be addressed separately. Most assemblies though will tie the second stud wall into both the ceiling and floor without the same break in materials that you have from one stud wall to the other. So your overall assembly is a double stud wall assembly, but your new stud wall transmits sound easily into both the ceiling and the floor. So the performance gains in the lab are significantly reduced. Not to mention the fact that you will lose in floor space at least the depth of the framing and a 3″ gap between the existing and new stud wall. That is a 6-1/2″ loss in floor space vs. a 1-1/2″ loss in floors space with resilient clips.
Independent joists – A great way to isolate the ceiling, but can become very complicated in the field. Here are a few problems with setting up a system like this. One, you won’t have much room for lighting and really no room for recessed lights since each joist will need to fit within two existing joists. Two, you won’t have much room for HVAC duct work. Three, if duct work, electrical, and plumbing already exist in between the joists then installing the independent joists can be very complicated. The only way to resolve these issues is to drop the entire joist, or most of the joist, beneath the existing joists rather than in between the joists. Problem is you will lose a serious amount of head room. Impossible for ceilings 8′ and lower without reducing head room to unusually low levels and not attractive for ceilings 9′ or lower. Independent ceiling joists will also require the use of double stud walls, or at least newly framed walls, resulting in both loss in head room and loss in floor space. It definitely works, but your room will really tighten up quick.