Green Building and Acoustic Considerations

With a good overview of some of the types of flooring systems and design issues that need to be addressed, let’s turn our attention to some performance issues specifically related to sustainability. When looking at the systems already discussed, here are some things to be aware of in terms of how they can contribute to green building certifications and environmentally conscious decision making in general.

• Composite floor systems: Long-span composite floor systems align well with green building programs such as the U.S. Green Building Council LEED v4 rating system. That’s because they support a holistic, long-term view of project performance and costs, both to the building owner and to the environment. The longer a building can remain in service, the fewer resources that are needed to construct a replacement. This applies not only to the building structure but also to interior changes. Long-span composite floor systems afford large open spaces that make it easy for internal tenant moves, additions to tenant space, or other configuration changes without requiring extensive demolition and disposal.
  
  
• Tile and stone mortar products: The best way to be sure that mortar and related products help with positive indoor air quality is to request product-specific environmental product declarations (EPDs) for mortars, grouts, and similar products used as part of a tile or stone floor. In addition, health product declarations (HPDs) can be requested to document that products are free of toxic chemicals. Either of these documents can help a project achieve LEED certification, however, not all manufacturers can provide the needed information. Therefore, if certification is important, then it is worth seeking out manufacturers that have taken the initiative to be transparent in their product formulations and can demonstrate their commitment to the environment through the use of safe ingredients and compounds. Mortars, including thin-set mortars, can be independently tested and verified by independent agencies for low levels of VOCs and other specific compounds. For example, Underwriters Laboratories Environment (ULE) is the exclusive provider of GREENGUARD Certification for products that meet stringent chemical emissions requirements and have tested and certified some mortars. As Mitch Hawkins, technical services manager of LATICRETE, points out, “The goal is to provide maximum disclosure so as to allow the design team and building owners a better opportunity to make more informed decisions when it comes to choosing what products will go into their projects.”
  
  
• Resilient flooring: As noted earlier, linoleum is the only resilient flooring material that is 100 percent bio-based from natural materials and is biodegradable. Based on this, independent life-cycle assessments (LCA) have been performed that prove that linoleum is far less harmful to the environment than vinyl and rubber. Thanks to a formulation that is free of the environmental toxins emitted by vinyl and rubber flooring, linoleum minimizes threats to current human health and the genetic wellbeing of future generations.
  
  
• Entrance flooring: An important purpose of entrance flooring is to improve indoor environmental quality. It is an integral part of a green building design because it removes and traps a bulk of the dirt and moisture from pedestrians’ shoes before they travel farther into the building. This keeps contaminants out of the building and is recognized as such in most green building certification programs. From a long-term durability standpoint, entrance flooring helps to extend the life of the interior floors and decrease maintenance needs. By requiring less chemical based floor cleaners, they help improve indoor air quality during building operations and maintenance.

Acoustics

Acoustics is increasingly recognized as a significant factor in green building standards and deserves some specific attention here. Most people think of acoustics in terms of walls or ceilings, but the reality is that floors, particularly in multistory buildings, have a role to play in good acoustics too. Several important distinctions need to be made since there seems to be a fair bit of confusion on sound and acoustic properties of flooring materials:

• Sound movement: When sound radiates through the air and strikes a material, some of that sound energy is absorbed, some is reflected, and some is transmitted through the material. How much sound follows each of those three paths is a function of the acoustic nature of the material it strikes. Individual materials can be formally tested according to ASTM C423 to measure the sound-absorption rate on a scale of zero to one. Hence a material with a noise reduction coefficient (NRC) of 0.0 can be presumed to reflect back all of the sound striking it (i.e., not absorb any), while a material with an NRC of 1.0 is represented to absorb or transfer all of the sound that strikes it. The NRC is useful for determining the sound-absorbing characteristics of materials in many general building applications and may be used for some flooring materials.
  
  
• Airborne sound transfer: Airborne sound that is not absorbed or reflected from a material is transferred through it to the other side. Hearing loud music or speech coming from an adjacent room is an example of airborne sound passing or being transferred through a wall. The same thing can happen in floors—the airborne sound can pass through a floor/ceiling assembly to the room above or below. How much sound transfers through an assembly is determined by the sound transmission class (STC) according to ASTM test methods. A higher STC rating (50 to 60 or above) means that more sound is blocked, while a lower STC rating (35 or less) means that more sound is transmitted through. The important thing to remember about STC ratings is that they are necessarily based on the entire floor/ceiling construction assembly, not just a single material. That means that the floor structure, any underlayments, any ceiling materials, and sound-deadening materials are as important as the floor material itself. Dense materials like steel and concrete are good at reflecting airborne sound, thus allowing very little to pass through resulting in higher STC ratings. Similarly, softer materials such as carpet or some resilient flooring are good at absorbing airborne sound, also producing higher STC results. Assemblies without enough reflection or absorption will transfer more sound through them.
  
  
• Structure-borne sound transfer: Sound can be created or emanate within a building structure or assembly, radiating outward from the structure into the air and to the ears of anyone nearby. In floors, this can happen when someone walks along an upper floor in hard-soled shoes or drops an object onto the floor. In this case, the separate impact insulation class (IIC) is used as a measure of the ability of a floor/ceiling assembly to absorb or deflect sound from such impacts and keep it from being transmitted to the space below. The IIC is only a measure of such structure-borne sound and not of airborne sound. In this case, hard surfaces, such as concrete or hardwood flooring, are a detriment since they will transfer impact sound quite readily. Resilient and carpet flooring can soften impacts and thus produce more favorable IIC ratings.

The first step in controlling sound transfer through floors, then, is to understand the nature of the sound transfer as summarized above and how to design a floor/ceiling assembly to control it. In most cases, both airborne and structure-borne sound will need to be addressed for successful acoustical performance. The structure and any penetrations needs to be looked at in terms of acoustics, and then the rest of the assembly can be considered. In some cases, it will make sense to install an added underlayment layer that can isolate the finish flooring from the structure and improve the IIC, although it may have some limited effect on STC ratings too.

The choice of finish flooring will make a difference in the sound transfer but also the sound qualities within a space. Since hard surfaces, such as concrete and tile, are good at reflecting sound, they may create echoes within the space that can make it difficult to discern speech or just create a higher level of background noise unless other acoustic measures are undertaken. Softer surfaces, such as resilient flooring, can absorb more sound and help reduce the degree of echoes or noise in a space. Overall, it is the acoustical comfort of the people using the facility that is sought to produce a healthier, more enjoyable indoor environment that is conducive to a variety of activities.

Photos courtesy of Forbo Flooring Systems/Andrew Latreille

Flooring systems and their role in acoustics are sometimes misunderstood. In the Chinook Regional Hospital designed by Perkins+Will shown here, resilient linoleum flooring is used as part of an overall floor assembly to reduce sound transfer to spaces below and minimize echoes within the space.