Installation Guide

28 SOUND CONTROL
Discussion of sound control in conjunction with ceramic & stone tile
SOUND CONTROL
Controlling sound transmission through floor/ceiling assemblies in multi-story construction can present challenges to architects and
design professionals, particularly when hard surface coverings, including ceramic and stone tiles, are used. This is because sound control
materials tend to be compressible and may not provide adequate support for the tile layer in thin-set applications. However, there are
practical methods that allow for the use of tile and stone while providing sound transmission control.
Sound transmission categories, evaluation, and code requirements
The first category is airborne sound, such as speaking, music, etc. Airborne sound transmission is measured using standard test methods.
For example, the ASTM E90 and ASTM E336 test methods are commonly used for laboratory and field measurement of airborne sound
transmission, respectively. The results from these tests are then used to calculate a single-number rating per ASTM E413 that is called sound
transmission class (STC) or field sound transmission class (FSTC).
The second category is impact sound, such as foot traffic, dropped items, etc. The ASTM E492 and ASTM E1007 test methods are
commonly used for laboratory and field measurement of impact sound transmission, respectively. The results from these tests are then used
to calculate a single-number rating per ASTM E989 that is called impact insulation class (IIC) or field impact insulation class (FIIC). The ASTM
E2179 test method was developed to provide a means of evaluating the flooring assembly’s contribution to a concrete floor. The contribution
of the flooring assembly to the IIC of the slab is calculated and reported as the ΔIIC (delta IIC).
Building codes typically contain requirements for both STC and IIC. For example, the International Building Code (IBC) calls out minimum
values of 50 for STC and IIC or 45 for FSTC and FIIC as an alternative to laboratory testing. The International Residential Code (IRC) calls out
minimum values of 45 for STC and IIC. Condominium associations may have their own minimum requirements for sound attenuation as well.
Factors affecting performance
Airborne sound transmission through floor/ceiling assemblies can be reduced effectively by increasing the mass of the assembly and
introducing suspended ceilings with sound insulation in the cavities. In general, STC ratings are largely independent of the choice of floor
covering. Furthermore, the methods used to improve STC ratings as called out above do not have adverse effects on the floor covering.
Thus, airborne sound transmission control is not a challenge to be addressed by the tile industry.
Impact sound control performance is dependent upon both the floor/ceiling structure and the floor covering itself. In general, impact sound
control with hard surface coverings is best achieved with floating systems that incorporate resilient layers.
A 6" (152 mm)-thick concrete slab will produce an IIC rating of approximately 28 without the floor covering or ceiling assembly. The direct
application of tile will not significantly improve the IIC rating. When flexible underlayments (membranes) are used in a thin-set assembly the
IIC rating can be improved, though the use of additional sound attenuation methods (e.g., sound-rated ceilings) are typically necessary
to meet required minimums. As resilient layers within a thin-set assembly are made thicker and more flexible sound control tends to
improve, but load-bearing capacity is reduced. This is the inherent limitation of thin-set assemblies for sound control. However, relatively
thick and resilient sound underlayments can be combined with a load-distribution layer (e.g., mortar bed, lightweight concrete topping,
poured gypsum underlayment) to provide excellent results (sound control meeting code minimums) without a sound-rated ceiling and
still provide good support for the tile assembly. For example, research has shown that a 1-3/8" (35 mm)-thick concrete topping over
1" (25 mm)-thick mineral fiber board on a 6" (152 mm)-thick concrete slab will produce an average IIC rating of approximately 60 to 65
without the floor covering or ceiling assembly, which far exceeds code minimums.
Wood-frame construction typically consists of a plywood or OSB subfloor supported on joists with gypsum board used to finish the ceiling
underneath. The first step in improving impact sound control is to ensure that the gypsum board ceiling is not directly attached to the joists.
Resilient channels are used to provide isolation between the gypsum board and the joists. Sound insulation batts are placed in the cavities
between joists as well. This type of assembly will produce an IIC rating of approximately 45 before the flooring assembly is installed. This
rating can be improved by increasing the mass of the assembly (e.g., adding another layer of gypsum board to the ceiling or plywood/OSB
to the floor). The direct application of tile over the subfloor can actually lower the IIC rating of this assembly. Using flexible underlayments
may mitigate this effect or even improve the IIC rating, but currently there is no standard test method available to quantify the contribution
of a flooring assembly to wood-frame construction in general. Again, the use of relatively thick and resilient sound underlayments can be
combined with a load-distribution layer to provide significant sound control and a solid base for tile installation.
Schluter
®
-DITRA
Schluter
®
-Systems has never promoted DITRA as a sound control system. However, DITRA provides a degree of sound attenuation
similar to various thin-set sound control membranes. DITRA and ceramic tile were tested* over a 6" (152 mm)-thick concrete slab and
the measured IIC rating of this assembly was 10 points greater than the measured IIC rating of the bare slab (IIC bare slab = 28, IIC slab
w/DITRA and tile = 38). This level of performance is not sufficient to meet typical code requirements without additional sound control
measures. As discussed above, the use of a sound control underlayment in combination with a load-distribution layer such as a mortar
bed, lightweight concrete, or gypsum concrete can significantly improve the IIC rating of the assembly. Sound-rated ceilings can improve
the IIC rating as well.
* Please note that this testing was performed prior to the approval of the ASTM E2179 standard test method and used a smaller specimen
size (4 ft x 4 ft) than required by existing sound control test method standards.
Installation Considerations
In laboratory testing, sound energy transmission is effectively directed through the test specimen only, with negligible transfer through other
paths. In other words, the values recorded provide an accurate picture of the sound control characteristics of the test specimen itself.
However, in construction, floor/ceiling assemblies and wall assemblies are connected to form the final structure and there is potential
for interaction between these elements. Floor/ceiling assemblies may not perform as expected in the field with respect to both airborne
and impact sound control if they are not isolated from adjacent walls to prevent sound energy transfer. Thus, perimeter joints serve to
accommodate expansion of the tile assembly and prevent “flanking” sound transfer. Schluter
®
-Systems provides a range of prefabricated
movement joint profiles that can be used to limit movement stresses due to changes in moisture content, temperature, and loading and
limit sound energy transfer.