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Maximizing Rubber Underlayment Performance

Rubber underlayment performs well in both concrete and 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 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 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. When combined with the extreme mass of the concrete, the resilient rubber underlayment adds high levels of isolation for both airborne and footfall impact noise transfer.

The easiest way to increase the performance of the rubber underlayment over a concrete sub-floor is to install a thicker rubber. The overall assembly performance will increase by decoupling the ceiling beneath the floor.

IN WOOD STRUCTURES

Basic wood structures start with higher IIC ratings (approximately 40 to 45 IIC) than concrete structures because they are lightweight and will flex. 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.

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 underlayment to deflect (compress) properly. Read the article Fixing Structural Deflection for more detailed information.

LAYERING MASS
Layer significant mass, approximately 7 pounds per square foot, directly to the sub-floor or over the top of the GenieMat. 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.

Layering the mass directly to the sub-floor will help most with isolating low frequencies for both airborne and footfall impact noise transfer. Most severe sound issues are low in frequency. Layering the mass over the GenieMat will lose some performance in low frequency isolation, but gain some performance in the mid to high frequency range.

Below is a reference table listing the weights of materials commonly used to layer mass in floors for sound isolation.

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

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