Maximizing Rubber Underlayment Performance

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Rubber floor underlayment performs well in concrete structures and can perform well in wood structures. The methods to maximize the performance of the rubber in these structures can be found below. To increase performance gains beyond the advice below, we suggest decoupling the ceiling with GenieClips® RST or resilient channel. The highest rated floor/ceiling assemblies will have significant resilience in both the floor and the ceiling.

IN CONCRETE STRUCTURES

Concrete structures have lower IIC ratings (approximately 28 IIC to 35 IIC) than wood structures because they are more rigid and massive. For those same reasons, concrete structures also respond best to resilient sound isolation products like rubber underlayment because the added resilience provides something sorely lacking from the basic concrete structure. Due to the inherent mass of the concrete, the resilient rubber underlay for wood and concrete significantly improves footfall impact noise transfer. Depending on the flooring type, some noticeable improvements for STC airborne noise can be achieved as well.

The easiest way to increase the performance of the rubber floor underlayment over a concrete sub-floor is to install a thicker rubber. The overall assembly can be further improved by decoupling the ceiling beneath the floor with resilient clips like the GenieClip® RST.

View our GenieMat® RST rubber underlayment for pricing and other information.

IN WOOD STRUCTURES

Basic wood structures inherently have higher IIC ratings (approximately 40 IIC to 45 IIC) than concrete structures because they are lightweight and will flex. And for these same reasons, installing rubber directly to a wood sub-floor will achieve less dramatic IIC gains than in concrete structures. This is because when someone steps on the rubber, the wood beneath will also give. As opposed to concrete structures, which have little or no give. The two best ways to resolve the flex in wood structures is through stepped blocking between the joists or layering mass over the sub-floor.

View our GenieMat® RST rubber underlayment for pricing and other information.

STEPPED BLOCKING
Fixing structural deflection can be resolved with stepped blocking. Stepped blocking is the process of increasing structural stiffness by adding framing within the joist cavity running perpendicular to the joists. This stepped blocking is the equivalent of another beam in the middle of the joist system. The rigidity created with stepped blocking takes the ‘give’ out of the wood structure allowing the rubber underlay for wood and concrete to deflect (compress) properly. Read the article Fixing Structural Deflection for more detailed information.

LAYERING MASS
Layer significant mass, adding approximately 7 pounds per square foot, directly to the sub-floor or over the top of the GenieMat® RST or GenieMat® FF. Any heavy material will work, i.e. plywood, OSB, MDF, drywall, lightweight concrete (best option of course), or a cementitious board like HardiBacker. Layering also provides an opportunity to add more damping to the floor with a product like Green Glue Compound. Including Green Glue Compound will add to the isolation of both impact footfall and airborne noise.

Where this mass is added to the assembly will have a little effect on overall gains. Layering the mass directly to the sub-floor will help most with isolating low frequencies for both airborne and footfall impact noise transfer. Keep in mind that most severe sound issues are low in frequency. Layering the mass over the GenieMat® RST or GenieMat® FF will lose some performance in low frequency isolation, but gain some performance in the mid to high frequency range, thus improving the STC airborne transfer rating a little more.

Below is a reference table listing the weights of materials commonly used to layer mass in floors for sound isolation. Adding mass is most important, not the type of mass added.

WEIGHTS OF COMMON MATERIALS

Reference Table For Weight of Common Building Materials
3/4″ lightweight gypsum concrete 6.5 PSF
1/2″ mortar bed 6 PSF
3/8″ plywood or OSB 1-1.2 PSF
1/2″ plywood or OSB 1.4-1.7 PSF
5/8″ plywood or OSB 1.8-2.1 PSF
3/4″ plywood or OSB 2.2-2.5 PSF
7/8″ plywood or OSB 2.6-2.9 PSF
1-1/8″ plywood or OSB 3.3-3.6 PSF
1/2″ drywall 2.2 PSF
5/8″ drywall 2.75 PSF
1/4″ HardiBacker or Durock or WonderBoard 1.9 PSF
1/2″ HardiBacker or Durock or WonderBoard 2.75 PSF
1/2″ MDF 2 PSF
3/4″ MDF 3 PSF