Underlayment is a term used for the padding placed below a floor. Underlayments serve as protection against moisture, they absorb sound, and they decrease subfloor imperfections. The padding is commonly made from foam, felt, rubber or cork, and usually comes in 100 sq ft rolls. You may also find padding already attached to the bottom of some laminate floor planks.
Placing underlayment padding can help with covering up minor imperfections and slight unevenness with a subfloor. Most floors require a slope or change of no more than 1/8” across any 6 foot span, and underlayment will not correct subfloors that do not meet that. Again, this is for minor imperfections. If your subfloor is littered with indentations and squeaky boards, the extra padding may make these flaws less noticeable but does not eliminate them. You would want to speak with a contractor if you need to completely correct these issues.
Laminate floors sometimes come with an attached pad that provides a great sound barrier and also makes installation easier. Sound blocking padding is measured by Impact Insulation Class (IIC) and Sound Transmission Class (STC) ratings. The higher rated pads will provide higher sound adsorption and resistance to impact noise. These do not block moisture. Even if the material could do that, each plank would have gaps, rendering the moisture barrier part ineffective.
The moisture or vapor barrier is used to protect your floor from water damage due to condensation from the subfloor, especially is the subfloor is concrete. Poly sheeting plastic can be placed down over your subfloor before installation to protect floating floors against moisture, and for any nailed or stapled flooring there are special paper underlayments. Most rolled underlayments come with a moisture barrier component so that you do not have to roll two different things over your subfloor during installation. They also come separately to be used under floors with attached padding.
There can be too much of a good thing. Placing down too much padding can wear out the joints and cause your floor boards to separate. If your floor planks already have an attached pad then you may not have the option of using additional padding. Read our earlier blog entry “How much 'stuff' can be under my laminate floor” for more information.
What is Needed When?
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