Construction Acoustics in Floor Systems

Header Graphic Acoustic in Floor Systems

Construction acoustics is the discipline that studies ways to control noise in rooms, buildings, and other environments by means of architectural design and acoustical construction methods. Construction acoustics is both a branch of applied acoustics and a division of structural physics.

Minimizing impact and airborne sound in any type of multi‐family dwelling begins in the design and specification phase.

With the growing number of multi-family dwellings, having a general understanding of the basics of sound control systems ratings and what they mean as they relate to flooring selection, is crucial. How to utilize proper sound control/attenuation systems to be in compliance is vital in the design-build stages of projects. Non-compliance can be extremely costly for all parties involved, and often involves litigation.

A number of factors contribute to a room’s sound insulating ability:

Floor/ceiling/wall construction and room size and shape.

Interior décor, such as wall hangings and curtains, and finishes and furnishings such as chairs, sofas, tables, and rugs.

Choice of floor covering material.

Use of a flooring underlayment.

Acoustic flooring system Facts Back

The cumulative effects of all of these components are what provides the final sound characteristics of the space. No single component can fulfill the requirements for the building requirements. These requirements consider the effects of the sum of these components.

In North America, there are two primary ratings used for sound control. They are Impact Insulation Class (IIC) and Sound Transmission Class (STC).

The protocol for specifying a flooring system is to first determine
the IIC, or STC requirements, then work with the builder, architect, and specifier to identify a flooring and underlayment combination
that aligns with the facility requirements.

IIC is a statistical measurement of the transmission of impact sound energy through a floor/ceiling assembly system (such as footsteps, dropped articles, or furniture moving across the floor). The larger the number, the more sound attenuation you have. The scale, like the decibel scale for sound, is logarithmic.

-Delta IIC is derived by subtracting the IIC of the nominal 6’’ bare concrete from the IIC of the various tested assemblies. The higher the Delta IIC, the higher the performance level.

-Field Impact Insulation Class (FIIC) refers to testing procedures conducted in the field where sound is not as controllable.

-Apparent Impact Insulation Class (AIIC) refers to testing procedures conducted in the field within the space directly under the tapping machine where sound from associated support structures is attributed to the floor-ceiling assembly.

-Sound Transmission Class (STC) is a rating of how well a building partition attenuates airborne sound (such as voices, radio, or television) in the context of multi-family facilities. STC values are influenced by the solid mass of the structure, but are also dependent on isolation and resilience within the structure.

-Field Sound Transmission Class (FSTC) refers to testing procedures conducted in the field where sound is not as controllable.

Builders, architects, and specifiers often use lab and/or field tests when specifying floor/ceiling assemblies. Lab tests are a more-accurate model for predicting attenuation performance in a range of different construction types. Field tests are accurate only for the site where the tests were performed.

When installing wood flooring in multi-family dwellings, in most jurisdictions, there are minimum IIC and STC values that the floor/ceiling assembly must achieve. It is necessary to take into consideration the building code standards including Uniform Building Code (ICC/UBC) or International Building Code (IBC), both of which call for minimum
50IIC (45IIC if field tested) and 50STC (45STC if field tested) values.

In addition to building code standards, many homeowners associations (HOA) have their own minimum standards written into their covenants, conditions, and restrictions (CC&Rs), which will supersede, and are often more-stringent than the minimum building code requirements. Specification of the proper sound control system with any floor covering change-out/remodel in existing buildings is just as vital in the design-build stages of new construction projects.

There are many different sound control systems and installation options when specifying the project. Installation methods may include floating, glue down, or nail down, but each method has its own unique variables to maintain the control of sound. Follow the flooring and underlayment manufacturer installation instructions and ensure the product used is a part of an entire sound control system.

Acoustical underlayments are especially important when specifying and installing wood floors for multi-level structures like apartment buildings, condominiums, or within commercial facilities. The use of acoustical underlayments for wood flooring is important for impact sound (IIC rating) such as footfalls, objects dropped on the floor, etc. The type of sound control system used will be dependent on a number of variables, including the type of flooring used, type of substrate, concrete thickness, ceiling suspension, framing structure, and the entire floor/ceiling assembly. 

Each acoustical underlayment system is designed to create an isolation barrier between the installed flooring system and what lies underneath. During installation, avoid hard surface transference points. The floor should not come in direct contact with any vertical obstruction. Never nail through an acoustical underlayment system, as doing so will compromise the specified IIC or STC ratings, as well as the long-term performance of the wood floor. The objective is to keep the entire floor assembly an isolated and independent unit. Some HOAs may have written in their CC&Rs to use acoustical foam in the expansion space, as well as acoustical sealant to meet their standard.

Acoustical adhesive systems are also available from many flooring adhesive manufacturers. These systems require a clear understanding of the application and how it influences the entire floor/ceiling assembly system. First, acquire third-party testing validation from the adhesive manufacturer for its published IIC and STC ratings. It is critical to use the proper trowel to ensure application allows for the intended outcome. The trowels used for sound control usually are specifically designed to allow the flooring to remain adhered to the subfloor, while leaving dead-space beneath.

With any installation method, the moulding should not come into direct contact with the flooring. A small gap should be left between the moulding and the wood floor. The moulding fasteners should be driven into the wall, and not into the flooring.

Controlling sound within any installation project is not solely the responsibility of the wood flooring installer. Sound control is a cumulative function of all of the components of the flooring, subflooring, underlayments, ceiling assemblies, and wall assemblies. The builders, architects, and specifiers on the project take into account all of these components and plan the project by specifying products and systems that, together, fulfill the IIC and STC requirements for the building. It is only the responsibility of the flooring installer to use products that conform to the specifications, and to install them according to manufacturer instruction.

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