Concrete walls and floors have long been the material of choice for reducing sound transmission (which is key to a better occupant experience) in the multifamily sector. Insulating Concrete Forms (ICFs) are often used for apartment and hotel projects due to their ability to isolate and dissipate noise. Controlling noise transmission in residential buildings is also important both for reducing interior noise between units and from the outside sources. Most multifamily buildings, whether they are apartment buildings or hotels, are generally located in urban centers where noise generated by automobile traffic can affect the occupant’s quality of life. No one desires to live in building where you can hear your neighbors.
So, what can owners of multi-family buildings do to meet the sound isolation expectations of their residents? Several techniques can be used to address these issues as it relates to construction methods and applications. For reference, every sound isolation problem has three elements:
- source – noise generator (loud stereo or instrument, voices, solid surface being struck)
- path – channel for sound-wave travel or a solid connection from source to receiver
- receiver – one hearing the source (occupant being disturbed – the residents)
To gain a better understanding of the impact normal everyday sounds have, the STC (Sound Transmission Class) and the IIC (Impact Isolation Class) methods of rating sound intrusion were specifically developed. See the following table to understand and gauge the effects of typical sounds (and their associated STC ratings) in residential environments:
In construction, there are three primary methods for improving sound isolation:
- Block – seal all gaps, cracks, and leaks. This is the easiest and most effective means to isolate sound. Sound will always find the weakest path—other attempts to improve sound isolation will be ineffectual if the gaps are not sealed first.
- Build Up – increase the mass of the construction. This makes it more difficult for the airborne sound to cause the partition to vibrate from one surface to the opposite side.
- Disconnect – introduce decoupling (breaks) into the construction. This allows one side/surface to absorb the vibrations without transferring it (i.e., block the path).
Given these methods of how sound infiltration is measured, we have data that quantifies attenuation within specific wall and floor assemblies. But be aware that designing to the minimum standard of the building code will not suffice for proper sound attenuation in multi-family / hospitality construction (typically the code accepts STC 45 or better). Building codes offer little in the way of acoustical privacy, so do not rely on “code conformance” to achieve acceptable acoustical performance. It’s necessary to evaluate and measure sound transmission reduction in all types of wall / floor / ceiling assemblies, and all sources of environmental noise or vibration in order to achieve adequate sound attenuation. The following are examples of typical STC ratings for walls assemblies. The IIC (Impact) ratings are not typically referenced for walls because the rating is a “strike” or contact measurement, therefore only STC is considered and typically referenced:
Oddly enough, the source of most sound infiltration (between units) in multi-family or hospitality construction does not come through the walls but instead broadcasts from overhead and below. With that in mind, the ability to control sound and vibration through the ceiling and floor structure is key. The following table is a comparison of the available floor construction assemblies and their typical average rating(s) for sound:
It is also widely known that floor finishes can assist in the overall sound rating (specifically IIC or impact) rating of floor/ceiling assemblies as well. The following finishes may contribute positively to increasing the control of sound transmission and the IIC rating of some floor assemblies:
- Pile Carpet Tiles with Rubber backing + 22 dB
- Pile Carpet on ½” Underlayment Pad + 32 dB
- Cushioned Vinyl Tile or LVT Plank + 16 dB
- Wood / Laminate / Engineered Flooring on Foam Underlayment + 15 dB
- Ceramic/Porcelain Tile on Cork/Rubber Underlayment + 15 dB
Concrete offers excellent noise control in two ways. First, it effectively blocks airborne sound transmission over a wide range of frequencies. Second, concrete effectively absorbs noise, thereby diminishing noise intensity. Because of these attributes, ICF walls and floors, concrete or precast planks, and composite concrete floor systems have been used successfully in multifamily, hospitality and theater applications to diminish sound infiltration and provide a much quieter environmental setting that fosters community while reducing property vacancy.
