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Flooring Underlayment - Types and Uses

Posted: Thursday, June 27, 2013

Introduction

We are often asked which underlayment is best when installing laminate flooring. This used to be easy to answer, but since the introduction of new underlayments with different features, it is a little more complex. However, this article should help you determine the best underlayment for your application. It will describe the different types and explain how they are used with laminate and engineered wood flooring.

When and Why Underlayments are Required 

Underlayment is required for any installation of laminate flooring or engineered real wood flooring. Both types of flooring are installed by a “floated,” or "free-floating," method, meaning they are not actually attached to the sub-floor. The individual boards are only secured to each other by gluing the mating tongue and groove edges or by simply clicking together the special joints of the “no-glue” type. The underlayment is placed over the sub-floor first then the flooring is assembled on top of the underlayment.

The function of underlayment is to absorb some of the minor (very minor) imperfections in the sub-floor; to help deaden sound when walking on the floor (since it is not attached to the sub-floor); and to slightly (very, very slightly) soften the feel when walking on the floor. It is very important to understand that underlayment for laminate and floating wood floors is not the same as padding for carpet. Unlike padding for carpet, a thicker underlayment will not make laminate or wood flooring feel softer. It will, however, reduce overhead sound in rooms below the flooring in addition to lessening the affects of sub-floor imperfections. The sound reducing quality is especially true of cork underlayment explained later in this article.

When choosing an underlayment for your new flooring, it is important to use only the type offered or approved by the manufacturer of your particular flooring. Besides the previously mentioned cork underlayment, there are four basic types of foam underlayment: standard foam, foam/film combination, Floor Muffler brand, and modified/upgraded.

Standard Foam Underlayment (Without Attached Moisture Barrier)

What is it? – The most common underlayment is standard foam. Most manufacturers have their own special name for this type of underlayment, but essentially it is all the same. Standard foam underlayment is simply a thin, foam padding measuring approximately 1/8" thick. The roll sizes vary from manufacturer to manufacturer, as do the prices. Some manufacturers offer this type of underlayment in 100-square-foot rolls and others offer larger amounts. Standard foam underlayment provides only a minimal level of sound reduction, comfort, and sub-floor correction. Because of its limited sound reduction capability, it should only be considered as a base grade, or entry level type of underlayment.

Where is it used? – Since standard foam underlayments do not have a moisture barrier attached to them, they are typically used where there is no possibility of moisture rising up from the sub-floor. In most cases, standard foam underlayment would be placed over a plywood sub-floor, but there are some instances where it could be used over concrete. For example, if you lived in a condo building and your unit was on the second floor or higher, or if the second floor of your home had a concrete sub-floor. Whenever you are installing flooring on the second floor, or higher, of a home or building and underlayment is required, a moisture barrier will not be required. (Note; if you are installing flooring on the second floor, or higher, of a home or building where more sound reduction is required, you may need to use cork underlayment. This is discussed further under Solid Cork Underlayment.) If you have a plywood sub-floor with a crawl space underneath, we recommend using an underlayment with a moisture barrier attached, or laying down 6mil plastic sheeting before the underlayment. Plastic moisture barrier is discussed further in the next section.

To review, if you have a sub-floor that is well above grade (above the ground, dirt, etc.), whether it is plywood or concrete, standard foam underlayment can be used. If you are installing flooring on the second floor, or higher, of a home or building then standard foam can also be used, providing you do not need sound reduction. If you need protection against moisture, standard foam cannot be used alone, but can be used in conjunction with a plastic moisture barrier, 6mil or thicker. If you are on installing flooring on a second floor or higher and require above average sound reduction (need to reduce the sound traveling to the floor below) then standard foam would not be the correct underlayment.

Combination Foam/Film Underlayment – aka Combo Underlayment

What is it? – Combination foam/film underlayment is essentially the same as standard foam except that it has a moisture barrier attached to one side. The moisture barrier prevents moisture from getting into the flooring from underneath and potentially causing major damage. As with the standard foam, manufacturers may offer combo underlayment under their own specific brand names, but the quality is fairly consistent. The thickness is the same as standard foam, and so is the level of sound reduction, comfort, and sub-floor correction. Also like standard foam, combo underlayment is sold in various size rolls, depending on the manufacturer. Because of foam/film’s limited level of sound reduction, it should only be considered for base grade, or entry level, use.

Where is it used? – Combo underlayment is used wherever there would be the possibility of moisture coming up from the sub-floor. Most of the time this would be on the ground level when the sub-floor is a concrete slab. As previously mentioned, if you have a plywood sub-floor that is over a crawl space, the combination foam/film underlayment is highly recommended to preserve your flooring investment.

Note: While it is very rare these days, some manufacturers may not offer the combo underlayment. If you need moisture protection, but the manufacturer does not offer this type of underlayment, then you will need to lay 6mil plastic sheeting down first then install standard foam underlayment over it. The 6mil plastic is acceptable to most manufacturers, but to be sure it will not void your warranty, check with your specific flooring manufacturer before using this method.

Floor Muffler Brand Underlayment – Our highest rated underlayment!

What is it? – The Floor Muffler brand is a closed-cell type of foam underlayment with an attached moisture barrier. While it is considered an upgraded or modified underlayment, which will be discussed in the next section, this product is uniquely different. Floor Muffler’s manufacturer put a lot of high-tech engineering into the development of this product. Their main goal was to eliminate the hollow sound, or echoing, that consumers sometimes complained about with laminate floors or other floated installations. Some of the benefits of the Floor Muffler product are:

  • Much less expensive than cork underlayment
  • Reduces reflective sound and through-the-floor sound transmission
  • Designed to provide a walk-on sound similar to that of traditional wood floors
  • Suitable for use over both concrete and wood sub-flooring
  • Exceeds recommended moisture permeability ratings for installation over concrete slabs
  • Optimal thickness for both comfort and stability
  • Helps eliminate sub-floor imperfections
  • Mold and mildew resistant and non allergenic
  • Adds R-value to improve flooring insulation
  • Strong enough for residential as well as the most demanding commercial installations

While this list of benefits may be impressive to read, the bottom line is it actually works! Over the years, many manufacturers have told us that they cured the hollow sounding floor problem, but when put to the test their products ultimately failed to perform. However, when we tested Floor Muffler, it did. While nothing can completely eliminate the sound, this product reduces it more than any of the others. Floor Muffler is our number one pick as an underlayment for floated floors.

Where is it used? – Floors Muffler brand underlayment can be used over concrete or plywood sub-floors. It is designed to be used with any floated installation – hardwood, laminate, cork or bamboo. Since the product has a built in moisture barrier, it can be used below grade, at grade, and of course, on above grade levels. Please see our notes listed in the next section regarding condo buildings. While the manufacturer states that Floor Muffler can be used with glued-down applications, we cannot offer comment one way or the other, because we have had no experience with it in that manner.

Modified or Upgraded Underlayment

What is it? – Modified or upgraded underlayments are usually thicker and/or denser than standard foam. These underlayments can be constructed from high-density foam, closed-cell foam, fiber, or rubber. Their main purpose is to provide better sound reduction than the standard foam type. The comfort level and sub-floor correction ability would be the same as with standard foam and combo underlayments. In most cases, modified or upgraded underlayments do not offer the same level of sound reduction as cork underlayment, and they cost more. We’ll discuss the features of cork in the next section.

As with the other underlayments, manufacturers of the modified or upgraded types have their own brand names. However, unlike the other underlayments, they will vary in thickness, type of construction, sound reduction levels, and overall quality. Also, they may or may not be available with an attached moisture barrier.

Where is it used? – Modified or upgraded underlayments are used to reduce sound and therefore, are primarily used on second floor levels or higher. While they are more effective than the standard foam or foam/film types, in most cases they are not as effective as cork. These types of underlayments should not be considered as "added comfort," only as added sound reduction.

Note: If you live on the second floor, or higher, of a condo building, there may be rules that dictate the type of underlayment required. The requirement may call for one that reduces sound even more than the modified or upgraded types. In such cases, cork is often the specified underlayment. However, if cork is not specified, then we highly recommend Floor Muffler as a less expensive alternative that will provide excellent sound reduction. If you do live in a condo, we strongly suggest getting a copy of the rules and verifying their requirements before buying any material. We also suggest that you get a letter signed by the condo board, prior to starting any flooring work, stating that your choice of underlayment is acceptable.

Solid Cork Underlayment

What is it? – Solid cork underlayment is just what its name implies: underlayment made from cork. In our opinion, cork underlayment is one of the better choices you have. Cork is porous, therefore, it breathes. As such, it resists trapping moisture, like rubber or other non-porous underlayments can. It is also a “green,” or environmentally friendly product, meaning it is a natural and renewable resource. With cork underlayment you will get optimum sound reduction. It is available in different thicknesses, but as you might expect, the thicker it is, the better the sound reduction. This is only true, however, up to about 6 millimeters, or roughly 7/16" thick. Beyond that, there would be no appreciable improvement. In some cases manufacturers will not warrant their flooring if it is installed over a cork underlayment thicker than 6mm. Although cork underlayment costs more than standard foam, it would be a good investment. In addition to cork’s sound reducing benefit, it also gives the flooring more of a solid-hardwood feel when walked on. This is especially important with laminate flooring.

Where is it used? – Solid cork underlayment can be used under most all floating laminate or wood floors. However, as with some foam underlayments, you may need to install a moisture barrier under the cork, if applicable. Most manufacturers accept 6mil think plastic sheeting as a moisture barrier, but to be sure check with your specific flooring manufacturer or with one of our flooring consultants.

Another use for Cork is to increase the height of the sub-floor. As an example, suppose there is ceramic tile throughout the living areas of your home, and carpet in the bedrooms. You decide that you want to install laminate flooring in the entire house including the bedrooms, but when you take up the carpet, the tiled area becomes a higher sub-floor. You can install the laminate flooring over the tile since the laminate is a free-floating floor, but what do you do about the height difference in the bedrooms? You could incur the huge expense and mess of ripping out the ceramic tile, or you could take the easy route and build up the sub-floors in the bedrooms with cork. Now you’ll be able to install the laminate flooring in the entire area without any changes in the finished height.

Another benefit of cork underlayment is that it can be used with most all wood flooring installations, including glued down, nailed down and stapled down. It can also be used under ceramic tile, cork flooring, and bamboo flooring. One important note: whenever you are installing flooring by a method other than free-floating, the cork underlayment must be glued to the sub-flooring as opposed to simply laying it down.

Summary

You should now have a good understanding of the different types of underlayments are and how they are used.

We strongly recommend using FloorMuffler underlayment for all free-floated installations. For all other installation methods, cork underlayment is your best choice, if your budget allows it. Although it is more expensive, it is the most stable and durable, and it offers the best sound reduction.

If you have any questions, feel free to contact us at (800) 764-1212 and select option #1 to speak with a flooring consultant.