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Flooring Underlayment - Types and Uses

This article discusses the different types of underlayments and how they are used for the installation of laminate flooring and some floating wood floors. A question we hear quite a bit is, "what is the best underlayment to use when installing a laminate floor"? Over the past few years, the manufacturers have made it a little difficult by introducing various types of underlayments with different features. The object of this article is to give you a general idea of what is available, and what may be the best choice for you.

When & Why are Underlayments Required?
Underlayment is required anytime you will be installing a laminate floor, or a floating engineered real wood floor. Both laminate flooring and floating wood floors are installed using a "free float" method, where they are not actually attached to the sub-floor, instead the boards are attached together. The underlayment gets laid down over the sub-floor, the flooring lays on top of the underlayment and gets attached together either by gluing the tongue and groove, or by locking the boards together if it is a "no-glue" type product.

Well that answers the when part of the question, now let's answer the why. The function of the 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 the flooring is not attached to the sub-floor, and to slightly (very, very slightly) soften the feel when the floor is walked on. Let me clarify one very important point that is a topic of discussion every time underlayment is brought up. Underlayment for laminate and floating wood floors should not be confused with padding for carpet. If you think you can buy a better or thicker underlayment and the floor will feel softer, you are wrong. Unfortunately there are some salesmen in the industry that are accustom to selling customers upgraded carpet padding, and now they are using the same sales tactics with flooring underlayments.

There are different types of underlayment available which we will discuss in the next few sections. It is important to mention that when choosing an underlayment for your new flooring, you must use underlayments that are offered, or approved by the manufacturer of the particular flooring you are interested in. The four basic underlayments offered in most cases are:

Standard Foam - a standard foam usually 1/8" in thickness without any moisture barrier attached
Combination Foam/Film - sometimes referred to as "Combo" underlayment - most of the time identical to the Standard Foam except there is a moisture barrier attached to the bottom

Modified or Upgraded Underlayments - these are available in different thickness and densities, usually constructed of a higher density foam, rubber, etc.

Solid Cork - Used only when required for maximum sound reduction. This product is generic and used mostly in condo buildings because the condo rules specify it be used.

Standard Foam Underlayment (Without Attached Moisture Barrier)

What is it? - The most common underlayment is the Standard Foam underlayment. Most manufacturers have their own fancy name for this underlayment, but essentially they are all the same. This underlayment is simply a thin foam padding, for lack of a better word, usually measuring about 1/8" thick. The roll sizes vary from manufacturer to manufacturer, as does the price. We have seen manufacturers offer this underlayment in rolls ranging anywhere from 100 square feet, to 1,300 square feet. Depending on the size or your flooring project, you may want to take advantage of the larger rolls if they are available. In most cases they are priced slightly less per square foot because you are buying in bulk. The standard underlayment offers a more than adequate level of topical sound reduction, comfort, and sub-floor correction.

Where is it used? - Since Standard Foam underlayments do not have a moisture barrier attached, they are typically used where there is no possibility of moisture coming up from the sub-floor . In most cases, this would be over a plywood sub-floor, however there are some instances where they would also be used over a concrete sub-floor. This would be 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 was concrete sub-floor. Whenever you are installing a floor that requires underlayment on the second floor or higher, be it in a home or a building, you will not need a moisture barrier and the Standard Foam will be an acceptable underlayment. (Note; if you are installing the floor in a building or home on the second floor or higher and require more sound reduction, a Modified or Upgraded underlayment may be required. This is discussed in another section below). If you have a plywood sub-floor and under the plywood is a crawl space, while it might not be required, we would recommend using an underlayment with an attached underlayment, or laying down a 6mil plastic prior to the Standard Foam. We will discuss the plastic moisture barrier further in the next section.

So let's recap. If you have a sub-floor that is well above grade (above the ground, dirt, etc.), whether it is plywood or concrete, the Standard Foam can be used. If you are installing a new floor on the second floor or higher of your home or building, the Standard Foam can also be used providing you do not need to reduce the sound traveling below the floor. If you need protection against moisture, the Standard Foam cannot be used, or it can be used in conjunction with a 6mil or thicker plastic moisture barrier. If you are on a second floor or higher, and require above average sound reduction (need to reduce the sound traveling below the floor), the Standard Foam will not be the choice.

Combination Foam/Film (sometimes referred to as "Combo" underlayment)

What is it? - Combo Underlayment is essentially the same as the Standard Foam except it has a moisture barrier attached to the bottom. This moisture barrier prevents moisture from getting up into the flooring and potentially causing major damage. As with the Standard Foam underlayment, each manufacturer may have their own specific branded name for this product, but they do not vary much in quality. The thickness is the same as the Standard Foam, as are the levels of sound reduction, comfort, and sub-floor correction. Depending on the manufacturer, the size of the rolls in which this underlayment is sold also vary. Again, if it is possible to take advantage of the larger rolls, the benefit is usually a slightly lower square foot price.

Where is it used? - The Combination Foam/Film 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 floor when you have a concrete slab (sub-floor). As we mentioned in the last section, if you have a plywood sub-floor that has a crawl space under it, in other words it's just above the ground, we would recommend using this Combo underlayment as an added precaution.

Note: While it is very rare these days, in some cases certain manufacturers may not offer the Combo underlayment. If you need moisture protection, but the manufacturer does not offer the Combination Foam/Film underlayment, then you will need to lay down a 6mil thick plastic first, and then install the Standard Foam underlayment over it. 6mil plastic is acceptable to most manufacturers, but make sure to check with the manufacturer of the flooring you are going to install if you have to use this method.

Modified or Upgraded Underlayments

What is it? - Modified or Upgraded underlayments refer to underlayments which are usually thicker and/or denser than Standard Foam. These underlayments are sometimes constructed out of a denser foam, closed cell foam, fiber, or rubber. Their main purpose is to reduce more sound than the Standard Foam type underlayments. These underlayments offer a higher level of sound reduction. The level of comfort and sub-floor correction would be the same as the Standard Foam and Combo underlayments. One misconception with this underlayment is that it reduces the topical sound dramatically versus the Standard Foam. If you are installing laminate flooring on a ground floor, Modified Underlayments will only slightly reduce the topical sound when you walk on the floor. Their main purpose is to reduce sound traveling below the floor.

As with the other underlayments we have discussed, each manufacturer has their own branded name for these underlayments. Unlike the other underlayments in this article though, they will vary in thickness, type of construction, sound reduction levels, and overall quality. As an added note, some of these underlayments are available with a moisture barrier attached, and some are not. Read the next section to get an idea of where these underlayments are most beneficial.

Where is it used? - Modified or Upgraded underlayments are most commonly used on a second floor or higher. In some condo building across the United States, if you live on the second floor or higher, they have requirements where if you install a laminate floor, free-floating wood floor, or ceramic tile, you need to use an underlayment that reduces the sound traveling down to the floor below you. These underlayments would also be used if you were installing the flooring on the second floor of your home and felt there was a need to reduce the sound below that level. You can use these underlayments on the ground floor of your home, but there will not be a substantial reduction in sound when you walk over the floor with hard heels for example. It will only be a minor reduction. With that in mind, you will need to evaluate your situation, and decide whether or not the added expense for this type of underlayment is necessary. As we mentioned in the introduction of this article, there are some dealers pushing this type of underlayment as they do upgraded carpet padding. This type of underlayment should not be sold as a product that will provide "increased comfort".

Note: In some cases, if you live in a condo building on the second floor or higher, they may have rules that determine what type of underlayment needs to be used. They may also require that you install underlayments that reduce the sound even more than these underlayments. In these cases, usually "cork" is an acceptable underlayment. We discuss cork in the next section. In our experience, if you do live in a condo, we would highly suggest getting a copy of the condo rules to see what is required. We also suggest that prior to the commencement of any flooring work, you get a letter signed by the condo board reflecting the type of underlayment you will be using and that it is acceptable to them.

Solid Cork Underlayment

What is it? - Solid Cork underlayment is simply constructed out of cork. The most commonly used cork is 1/4" thick, but the thickness may vary depending on the vendor selling the material. The Cork is generally only used when it is required, because the cost is much higher than other underlayments, and it has to be glued down to the sub-floor. The cost of Cork varies, ranging between $0.75 to $1.50 per square foot, plus the cost of the Cork installation. The sound deadening level of Cork is very high. It does not increase the comfort of the floor. Also, when installing cork the sub-floor must be flat.

Where is it used? - Solid Cork underlayment is used when a high level of sound reduction is required. As we mentioned in the previous section, we are referring to the sound traveling below the floor, not the topical sound you hear when you walk on the floor. Cork is most commonly used in condo buildings where it is a requirement. Cork underlayments are usually 1/4" in thickness. They are installed by being glued directly to the sub-floor, and then rolled with a weighed roller. Cork underlayment can be used as an underlayment for the installation of laminate floors, free-floating wood floors, as well as ceramic tile.

Another use for Cork is to increase the height of the sub-floor. Here is an example. Let's say that 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. You are now faced with a height difference. The difference being that when you take up the carpet in the bedrooms, the tiled area will be higher than the bedroom sub-floor. You can install the laminate flooring over the tile since it is free-floating floor, but what do you do about the height difference in the bedrooms? You can go through the huge expense and mess of ripping out the ceramic tile, or take the easy route and install cork in the bedrooms prior to the laminate flooring. The cork will bring the height in the bedrooms up to the same level as the ceramic tile. This way, you can now install the laminate flooring in the entire area without any changes in the finished height.

Once you have read this article, you should have a good understanding of what underlayments are and how they are used. The decision to use one underlayment over another is, in most cases, is a personal one, unless of course a specific underlayment is required. One thing that we have found since we started selling free-floating type floors many years ago, is that in some cases using a thicker underlayment can sometimes actually make the floor sound more hollow than with the thinner types. In our opinion, this is common sense. The farther away you get the flooring from the sub-floor, the larger the gap or area where sound can be trapped. In plain English, the larger the space, the more hollow the sound. This is not true though if the underlayment is the same thickness as a standard type, but much denser.

Bottom line, figure out what underlayment is best for you and don't go overboard. If you feel that the standard type underlayments are right for you, they probably are. Don't loose sleep over it. There are more important things in life to be concerned with.


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