Everything You Need to Know About Flooring Underlayment – Part II

In the previous post, we discussed what flooring underlayment is and its various types. In this post, we’ll concentrate on the important functions underlayment serves.

Using Underlayment for Sound Dampening

Flooring sound transmission is a problem most homeowners face, especially with hardwood or tile flooring. When hard objects like high heels, hard-soled shoes, furniture, pet claws, etc. meet the floor, a loud sound is emitted. Whenever a person walks upstairs, downstairs, in an adjacent room, lobby or drops something, sound transmits through the floor below or migrates above through ceilings. Often, sound waves spread and get amplified through collisions with the walls and furniture, creating an echo. Underlayment counters this by absorbing the sound waves between floors and within the rooms.

Foam, felt, rubber, cork, cement board and acoustic underlayment have the best sound surpressing qualities. Your choice will depend on the flooring type installed.

Polyethylene foam, acoustic foam and recycled felt foam are good underlayment materials to use underneath carpeting, laminate and hardwood flooring. Out of these three, polyethylene foam is the most economical choice with its basic sound-blocking properties. Recycled felt is twice as expensive compared to polyethylene, but it delivers the best sound-proofing.

For hardwood flooring, cork underlayment provides the best sound reduction. It’s glued down to the subfloor during the floor installation. Cork is popular among condo associations that have rules regarding sound levels. Cement board underlayment (CBU) works best for tile flooring.

Using Underlayment for Moisture-Proofing

Moisture, if not controlled, is a danger to flooring. Moisture coming up through the subfloor can damage your carpeting, laminate and hardwood flooring. You must test the relative humidity (RH) of your subfloor before installing your floor product, especially if it is concrete. If the RH isn’t within the acceptable range, the underlayment will fail to prolong the life of your floor, no matter how superior its quality is.

When a floor covering is placed on concrete, the humidity in the concrete equilibrates. It distributes the humidity across every direction, pushing the higher levels of moisture at the bottom towards the top. If moisture comes in contact with your flooring, it’ll damage it. According to industry standards, 75% relative humidity is acceptable for all flooring types. A higher RH means the subfloor can potentially cause dampness under the flooring after it’s installed. The increased dampness raises the alkalinity of concrete which is responsible for flooring damage.

Some underlayment types have a built-in moisture barrier. It protects from different moisture-related troubles like mold, warping and gapping. The underlayment can also be installed along with a separate moisture barrier if it doesn’t have it built-in.

When choosing an underlayment types, make sure your flooring doesn’t have one already installed. Many laminate floors come with extra padding. Too much padding can hamper the locking system of the floor by weakening the joints and causing separation of the floor boards.

We hope this guide will help you make the right decision about your underlayment needs. At the very least, when you discuss it with a professional flooring service, you’ll know what each type stands for.

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