Triple Leaf Effect – Retrofit Installation
A triple leaf partition has two air cavities rather than the typical one air cavity. Similarly, a quadruple leaf partition has three air cavities. Triple and quadruple leafs are most often created when constructing a new wall in front of an existing wall. The other common way is by installing resilient sound clips or resilient channel over existing drywall. This applies to both sound insulation for walls and ceilings alike. A leaf in a partition is a solid layer, like drywall or plywood. A leaf can have multiple layers without any problem because there is not an air space between each layer.
The drawings above show single leaf (no air cavity), double leaf (like most assemblies), triple leaf, triple leaf created by using resilient clips over existing drywall, and a quadruple leaf assembly. In the sketch below, we show again double, triple, and quadruple leaf sound insulation for walls with varying distribution of drywall layers.
It is not illogical to presume that the quadruple leaf block walling on the far right would block sound better than the other examples. After all, the sound has to go through drywall, air space, drywall, air space, drywall, air space, and then again drywall, often with wall sound insulation within each air space. In a double leaf block walling, the sound has to make it through only one air leaf space. While it makes sense to think that, it is, unfortunately, not the case.
TESTING FOR COMMON WALLS WITH MULTIPLE LEAFS
The STC values shown above for the common framing assemblies are from a series of tests commissioned by Owens Corning and Pliteq ( GenieClip® RST ). While STC does not tell the entire story, it is clear that the triple leaf and quadruple leaf assemblies should be avoided whenever possible.
TESTING FOR CLIPPED ASSEMBLIES WITH MULTIPLE LEAFS
The STC values shown above for the GenieClip® RST assemblies are the results of independent tests. The performance loss created by the retrofit clip installation was significant, but lessened by insulating the space between the existing drywall and new drywall with an R-8 insulation. The retrofit performance would have been much lower without the extra insulation.