Change of State

While many people don't tend to think about this heat flow process, we are all likely aware of it most commonly in water. When liquid water changes into solid ice at cold temperatures or into a gaseous vapor at warmer temperatures, this is a change of state, or phase change which results in a gain or loss of energy. In buildings, water vapor phase change can contribute to actual or potential heat transfer. HVAC engineers will usually take this into account as latent heat in a building and plan on addressing it particularly in air conditioning scenarios. From a building construction standpoint, it becomes important to be sure that water vapor is restricted from entering construction assemblies, not just for the potential damage from condensation that may occur in the cavity, but also from the change of state that will induce other heat energy variables on the heating and cooling of the building.

 

Building Insulation for Acoustical Quality

Sound energy radiates outward from a source much the same way that heat energy radiates outward in all directions. If the sound is essentially airborne, as in people talking loudly, the sound will travel through the air and disperse into lower concentrations until it can no longer be heard. Alternatively, it may strike a building material surface and be reflected back into a space or it may penetrate the material or construction assembly and transfer through it. In buildings or complexes where multiple activities are occurring or privacy is desired, this airborne sound transfer through common walls, floor, and ceilings becomes an important design consideration.

Similar to heat transfer, sound transmission is affected by the density of the materials that it encounters and the characteristics of the type of sound energy. Heavy, dense materials like concrete and masonry will not transmit airborne sound well, rather it will tend to reflect or disperse it throughout the materials just as a radiant heat barrier will reflect and disperse heat. A non airborne sound, such as banging on a masonry wall, is a structure borne sound that will also disperse through the material, but in this case could transfer or conduct quite well. The net result is that an airborne sound on one side of the dividing assembly measured at a loud level will be reduced by the divider down to a notably softer level or will no longer be heard. A loud structure borne sound may not be reduced much at all and may be still be considered to be loud on the other side.  Controlling these sounds then becomes a matter of designing and specifying the walls, floors, and ceilings around common spaces to address the sound conditions encountered.

When dividing assemblies are not solid, but made of lighter weight, less dense assemblies such as metal or wood framing, structure borne sounds may be diminished, but airborne sounds become the greater concern. Rather than adding heavier materials, sound energy transmission can be impeded by insulation materials much the same way they impede heat energy transmission. In this case the Sound Transmission Class (STC) rating becomes the testing standard for determining performance of materials. Once again, it is a controlled ASTM test that measures the transmission loss (TL) of sound through a selected material or assembly and compares it to a standard ASTM benchmark to establish an STC value. The laboratory test is the best indicator of performance, but like U and R value testing, actual field conditions may vary that influence the actual performance.

In selecting an insulation product for addressing sound control, it is important to look at the rating of the entire tested assembly and be sure it is comparable to the design of the assembly in your particular design to predict performance accurately. Typical versions of un-insulated framed partitions with gypsum board generally achieve an STC rating in the range of 30 − 39. In these situations, it would be fairly safe to assume that there are few secrets between occupants on either side of such a partition. Adding insulation to the cavities can dramatically improve performance, usually achieving STC ratings in the preferred range of 40 − 60 depending on the application. A big part of the difference is in the ability of the insulation itself to reduce sound. Different insulation materials can be tested independently and a Noise Reduction Coefficient (NRC) can be determined. The NRC is defined as a single-number index determined in a lab test and used for rating how absorptive a particular material is. This industry standard ranges from zero (perfectly reflective) to 1 (perfectly absorptive).  Note that, based on the testing methodology, and depending upon the material's shape or surface area, some products can actually test at an NRC above 1. The higher the NRC rating of a particular material, the better choice it will be for use as an acoustical insulation material since it will boost the STC rating and improve overall sound transfer performance.

 

Peter J. Arsenault, FAIA, NCARB, LEED-AP  is an architect and green building consultant based in Upstate New York focused on sustainable design and practice solutions nationwide. He can be reached at www.linkedin.com/in/pjaarch

Bonded Logic Inc. manufactures recycled insulating products that are good for both you and the environment in which you live. With a focus on performance and sustainability, Bonded Logic has a solution for your insulation challenges.  www.bondedlogic.com