Volume 21, Issue Number 3, Spring 2016
Repairs, Maintenance and Renovations
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Noise in Condos
Demystifying Flooring Acoustics
By Jeff Cowx | Other articles by Jeff Cowx
More than ever, choosing the right acoustical solution, especially when it comes to flooring, represents a substantial challenge. Achieving lower noise pollution is essential to reducing stress, anxiety and achieving desired/deserved comfort. This is not as allusive as one might think. When working with a condo owner or on a new multi-family project, asking the right questions, at the right time, is crucial. To meet (and often exceed) impact and airborne sound requirements, we need more than just a fictitious number. The following may be helpful when navigating through this complex, and often misguided field.
Types of Noises, Measurement Units and Acoustic Standards
First it is important to differentiate the types of acoustic sounds in our homes. By definition a noise is a sound, especially one that is loud or unpleasant or that causes a disturbance. As you are no doubt aware it can also be the leading causes of conflict.
Airborne or impact Noise
Sound Transmission is rated: either by Airborne or impact noise. Each of these requires a different solution to mitigate them, particular to the application.
Airborne Noise: Airborne noises come mainly from radio, television, voices, etc. (you may have some others you would like to add). An airborne noise is a sound wave carried by vibration through the air which penetrates surfaces such as floors, ceilings and walls structures. Airborne noises also transmit through all the small openings in the building (around doors, air vents, electrical outlets, etc.). It is therefore important to seal where possible all small openings. Ultimately, the more mass, the greater it will absorb energy and will reduce airborne noise.
In acoustics, there are three units of measurement for airborne noise: STC (Sound Transmission Class) or STI (Sound Transmission Index) when tests are performed in a laboratory, under controlled conditions and FSTC (Field Sound Transmission Class) similar tests conducted on site. Both tests are designed to determine the decibel reduction in noise that a partition can provide. Results of laboratory test, are 2 to 5 points higher than those having been performed on site. The National Building Code (NBC) requires a minimum of 52 STC for condominium, while the Canadian Mortgage and Housing Corporation (CMHC) require an FSTC 55.
Impact Noise: Impact sounds, are noises that are created by an impact or vibration, such as moving furniture, a person walking with high heels, falling objects on the ground or a child running. These are transmitted by vibration through the structure of the building, such as floors and walls. The measurement unit for impact noise is IIC (Impact Insulation Class), which results from laboratory tests. Like airborne noise, when you add an F before, FIIC (Field Impact Insulation Class), we refer to tests having been carried out in the field. As was true of acoustical ratings for airborne noises, these tests are designed to determine the decibel reduction in impact sounds through a substrate.
While there are no requirements in the National Building Code (NBC) for impact sound mitigation, some degree of control is necessary for occupant comfort and satisfaction. Therefore NBC does recommend a minimum of 55 FIIC in residential buildings to address the rights of its owners.
How to Reduce Noise?
Although there is some commonality among the factors influencing the attenuation of airborne sound and impact sound the latter is by far the more complicated to measure, rate and control. Due to the fact that impact noises generate much more energy than airborne noises, they travel more easily and quickly through the building structure. To ideally dissipate this energy, we must "decouple" materials as close to the source of the impact as possible. A resilient acoustic membrane is designed to eliminate this direct contact between materials. In a perfect world, the floor covering should never come in contact with the structure (substrate).
Challenges in Choosing an Acoustic Membrane
Typical Scenario: Mr. and Mrs. Smith want to change the flooring in their condo. The building they live in requires acoustic performance of FIIC 62. During their search they discover an acoustical membrane claiming an acoustic performance in excess of FIIC 62. They feel confident and proceed with the installation. The following week, their downstairs neighbor complains of hearing footsteps. An Acoustical Engineer is asked to perform acoustic tests on their flooring. The test results reveal a rating of FIIC 54, well below the FIIC 62 required. What happened? How can the results be so poor?
Flooring acoustics are far more complex than they appear. Indeed, several criteria must be considered when choosing an acoustic membrane. We cannot rely solely on the acoustic results published by the product manufacturer without paying attention to the floor / ceiling assembly.
Don't be Fooled
Be cautious of acoustic ratings published by manufacturers. It is impossible to predict the performance of an acoustical underlay without considering the nature of the building in which it will be installed. However, acoustic performance, as published by several acoustic membrane manufacturers, suggest that you can achieve similar results regardless of the type of structure. Therefore, it is essential to verify the conditions under which the published acoustic tests were performed by the manufacturer.
Was the testing conducted in a laboratory (IIC = Impact Insulation Class) or in the field (FIIC = Field Impact Insulation Class)? Acoustic tests performed in a laboratory, under ideal conditions, will systematically provide more efficient results than field tests, where nothing is optimal, often by up to 5 points. Was the floor / ceiling assembly used during the acoustic testing the same as the intended installation? The thickness of the concrete slab, the quantity and thickness of plywood layers, the use of resilient channel, the existence of a suspended ceiling, acoustical mat, etc. are all factors that can dramatically influence published acoustic results for a given membrane. As an example, a suspended ceiling can increase results up to 14 points. You must ensure that acoustic tests carried out with the membrane you are considering were conducted using identical or very similar testing methods and floor/ceiling assemblies.
Do Not Underestimate
An extremely important criteria in choosing an acoustic membrane is mechanical performance. Make sure that the product meets the mechanical criteria (thickness, density, internal cohesion) of the chosen floor covering. This aspect is often overlooked, however it is just as important as the acoustic performance. Neglecting mechanical performance while choosing your acoustic membrane can lead to expensive failures such as deformation, delaminating, cracking or lifting of the floor covering; all potentially voiding the manufacturer's warranty!
It's also important to know the type of flooring that will be installed: glued or floating engineered wood, nailed hardwood, vinyl, ceramic, etc. This information will guide you to the appropriate acoustical membrane category for your building. If the flooring type is not considered, the result may be that the membrane is too thick, soft or dense. Also, the membrane's mechanical strength may not sufficient enough to absorb the energy from the natural variations of the floor or subfloor.
As specialists, we lead the way, guiding our customers toward making educated decisions. Today, it is impossible to do so without having a better understanding of acoustics and evaluating the consequences of our recommendations. The good news is that the proper information and support is available and within reach.
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