Understanding Underlayment - An Integral Part of Your Flooring Installation

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Not a floor covering and not the subfloor, but what you can’t see – the floor’s underlayment. It is just as important and deserves just as much attention. Underlayment is one of the most important aspects of any flooring project in both residential and commercial settings. Proper selection and installation of underlayments is crucial to the wear and stability of any flooring.

What is flooring underlayment? 
Underlayment, or “padding”, as it is often called, is a thin material that rests between the floor covering and the subfloor. Because underlayment is a catch-all term, it can take different forms such as a soft foam or felt, cement board, fiberboard, or plywood. Its purpose is to provide a smooth place for the floor covering to rest, to dampen sound, and, in some cases, to act as a moisture barrier. 

How does underlayment work?
Underlayment does 3 things that are critical to a successful flooring installation:

  1. It takes out any minor deviations in the subfloor
  2. It delivers superior acoustical performance
  3. It acts as a moisture barrier 

If installing a floor covering over concrete, a "combination underlayment" such as Eco Ultra Quiet is suggested. For laminate and engineered hardwood, this underlayment has an IIC rating of 73 and a STC rating of 73. Ratings like these vary depending on the type of floor covering that is going to be installed. 

What does IIC and STC ratings mean? 
Sound insulation products like underlayments are typically specified for condominiums, hospitals, schools, hotels, office buildings and customers desiring quieter floors. Under the current Sound rating system, the higher the number the better sound suppression quality. In other words; rooms become increasingly quiet as the rating number increases. 

  • (IIC) Impact Isolation Class: IIC refers to testing of impact sound energy through a floor/ceiling assembly system. These types of sounds are the equivalent of foot traffic, dropped items, or moving furniture. 
  • (STC) Sound Transmission Class: STC refers to testing of airborne sounds through buildings such as a wall or floor system. These types of sounds are the equivalent of voices, music, and television audio. 

Many residential and commercial properties are now requiring minimums of sound control ratings in the high 50's or low 60's range. An underlayment, such as Sound Solution with Vapor Bloc, is great for most laminate and hardwood floor covering applications. This premium acoustical underlayment has an IIC rating of 73, an STC rating of 67, and a breathable moisture barrier. 

Is a moisture barrier necessary?
When installing hardwood flooring or laminate flooring, you want to protect your investment.  Moisture is a big concern for flooring, as in you definitely don’t want it! And not just water spilling or pet accidents. Moisture can come up through your subfloor, especially if you are installing over concrete or below-grade. A moisture barrier is needed to protect the flooring against moisture or moisture vapor. 

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Some underlayments have a built in moisture barrier. These are typically used for floating floor applications.  If you live in a condo, many have HOAs have rules regarding noise levels and often require you to secure an underlayment with high IIC and STC ratings. In this case, installing a laminate floor that already has a pad pre-attached over another underlayment is not recommended. Too much padding can lead to a weakening of the joints, resulting in the floor separating.  

As you can see, flooring underlayments play an important role in any hardwood flooring or laminate flooring installation project. When searching for an underlayment, make sure you find out what works best for your flooring needs or consult your local flooring professional for information. This will allow you to have the best experience you can and ensure your beautiful new floors last a lifetime!