soundproof floor underlayment

Do I Need Soundproofing Underlayment?

Absolutely not. As long as you are not terribly concerned about noise. Footsteps. Loud conversation. Louder music. Kids running. Things falling. You get the idea. Life going on around you. But if, or when, you decide to replace your floor covering; or if you are building a new home, soundproofing the floors should be a serious consideration. You are going to install underlayment almost everywhere anyway, so why not upgrade to a higher quality product that provides more, and better, soundproofing?

 

Definitions and Ratings

Bare with me while I provide enough background information to help you make an informed decision. I am not a big fan of ‘Buy this because I say so.’ type of blog. It is your money, your effort, and ultimately, your lifestyle. Make sure your choices work for you. Trusting some guy on a blog (even me–hard as that is to believe) may not be in your best interest. Hence, the following information–which I will be using throughout the article.

 

Types of Noise

1. Airborne Noise – Sound that is transmitted through the air (seems like a fairly obvious definition). Some examples are conversation, TV, music, and external noise such as traffic passing by, dogs barking, kids playing. Please see Designing Buildings Wiki for an expanded explanation.
2. Impact Noise (sometimes referred to as Structure-borne Noise) – Sound that travels through the structure of a building. Such as someone walking, something being dropped, ball bouncing. The sound will travel through floors, walls, and ceilings. Please see Designing Buildings Wiki for an expanded explanation of Impact Noise and some of the possible adverse health effects.

Airborne Noise will travel in every direction so it could be annoying in rooms below, above, and to the sides. Impact Noise is more likely to be heard from below. The structural vibrations caused by  Impact Noise can generate Airborne Noise in the adjacent rooms–in all directions.

 

Noise Reduction Ratings

Most soundproofing products will use one, two, or all three of these rating systems. Knowing a little bit about each of them will make you a more informed consumer. Which will help you make better investment decisions.

• STC (Sound Transmission Class) – STC is a rating system developed to measure a material’s ability to block sound. A higher STC rating means that whatever you are using blocks more sound from moving through floors, walls, ceilings. The following table is from Wikipedia – Sound Transmission Class where you can find more information on the subject.

STC	What can be heard
25	Normal speech can be understood
30	Loud speech can be understood
35	Loud speech audible but not intelligible
40	Loud speech audible as a murmur
45	Loud speech heard but not audible
50	Loud sounds faintly heard
60	Good soundproofing; most sounds do not disturb neighbouring residents.[6]

• NRC (Noise Reduction Coefficient) – NRC is a rating system designed to measure a material’s ability to absorb sound. The system rates product between 0 and 1. A rating of 1 suggests that the material soaks up all of the Airborne Noise. (Theoretically. I am way too old and cynical to believe that. Specially when I have seen things rated at NRC 1.05. How does that happen when 1 is supposed to be perfect?) The rating system is basically a percentage. Therefore a rating of .65 means 65% of the sound is absorbed. The following small table is from Wikipedia – Noise Reduction Coefficient where you can find more information on the subject.

Difference in Coefficient	Effect for Most Situations
0.05-0.10	Little
0.10-0.20	Significant
0.20 and above	Considerable

• IIC (Impact Insulation Class) – This rating system was devised to measure a material’s ability to block and/or absorb Impact Noise. Specially on floors. As with STC and NRC rating systems, a higher number will make you happier.  Wikipedia – Impact Insulation Class does not have much to add but please feel free to link to them or you can check out acoustics.com

The International Building Code requires a minimum 50 rating for both STC and IIC for all floor assemblies. Some local building codes have increased that requirement to the high 50’s and 60 range for multi-level construction to help ensure as much peace and quiet as possible.

Soundproofing Underlayment Construction Notes

Because I am a construction guy first, I need to put in this section. There are very few things more annoying than spending time and money on new floor covering complete with good quality soundproofing and walking across it for the first time and hearing it squeak. Now what? Well, not much other than living with it or taking up your flooring and fixing it. If you have used good underlay it will not be the new flooring rubbing on the subfloor. It will almost invariably be the subfloor sliding up and down on a nail or rubbing on the floor joists. If you have read some of my other posts like How to Soundproof a Floor, you know what is coming. Glued and screwed! I have a tendency to be a little anal about some things.

 

New Home Construction

Your builder should know this, but some times they need a nudge, and horror of horrors, framers have been known to take a shortcut or two. Each floor joist should have a bead of construction adhesive applied before the subfloor is installed. Without breaks in the beads. (Just before the subfloor goes down–not yesterday because it will be hard and leave a lump in the floor.) Then screwed down with 2″ deck screws about every 6″. If done properly, your floor should be squeakless for decades.

Note: At least one person on site will tell you a 2″ nail driven in with an air nailer is just as good. Horsepucky! The only one who benefits is the guy putting it down. Air nailers are quicker and easier.

 

Renovation Flooring

Unfortunately, you cannot re-glue an existing subfloor. Unless you plan to tear it up and start over. Which may be necessary if it got wet and is rotting or swollen. If that is what needs to be done, glue and screw the new plywood as described above–after making sure the floor joists are clean, smooth, and dry. 

Otherwise, add lots of screws (2″ minimum. Sometimes the floor has been re-done before and you will need longer screws to get a good bite into the joist.) to the existing subfloor–every 6 inches. Stand or kneel as close to wherever you are screwing to make sure the subfloor is as tight to the joists as you can make it. Walk on it when you are finished and listen for any sounds. Once the subfloor is as quiet as you can make it, you are ready to put down new flooring.

 

Soundproofing Your Flooring

Hopefully, I did not make your eyes glaze over with all of that. Now we can get to the meat of the article. I will give you my suggestion for the best product for each type of flooring, along with a couple of others I think are worth considering. (Note: When I see a list of 8, or 14, or 20, or 193 I tend to lose interest after about #3. Anyone can give you a list of 20 nails for instance. After you see the one you need; do you really care about the rest?)

Depending on your home, soundproofing some floors is more important than others. If you are living in a rancher, a mobile home, a house with only a crawl space below, or if nobody is ever in your basement; Impact Noise will not affect anything below. It does, however, have the possibility to transfer to the adjacent rooms by traveling through the framing structure. Airborne Noise will also travel through walls and ceilings.

On the other hand, if your house is a 2 story (or more), has a basement with bedrooms or family room, or if you live in an apartment building, both Airborne Noise and Impact Noise will be your enemies. Airborne Noise will be heard through the walls, ceilings and floors; as will Impact Noise. But Impact Noise will certainly be heard in the rooms below–unless you are banging on the ceiling with a broom).

Following are some suggestions to reduce, or in some cases eliminate, noise passing from one room to another through the floor. (Note: I found someone in the United Kingdom who recommends lead sheathing–given its mass–as the best floor soundproofing. Hauling lead sheets to the second floor, installing them, and then trying to nail down hardwood flooring seems stupid. Rest assured, I will not be mentioning this again.)

 

Best Soundproofing Underlayment for Rug and Carpet

A good thick carpet, or rug, (especially a wool rug) will provide significant help for sound insulation–like footfall noise–but does very little for soundproofing. The foam underlay recommended by the supplier will probably be designed to support and extend carpet life–with little thought about soundproofing. (It might also be ‘free’ to enhance sales.) Assuming it is fairly thick and dense it will also help with footfall noise.

 

Wall to Wall Carpet

The following three types of carpet underlay is designed to reduce both Impact Noise and Airborne noise.

• QuietWalk Plus – Manufactured by MP Global this product is not specifically designed for carpet. Most soundproofing products are not specifically designed as carpet underlay. It is designed for soundproofing. You will need to install carpet underlay over it. You can see all of the product specifications at mpglobalproducts.com but here are a few of the highlights:

– STC rating of 66 and IIC rating of 71 (when installed on the floor assembly)

– Vapor barrier, Moisture protection, Compression resistant, No volatile organic compounds or off gassing

– Approved for infloor heating systems and concrete floors

 

• Premium Carpet Underlayment – Available from tmsoundproofing.com This product is a combination of dense foam and Mass Loaded Vinyl (MLV) with an STC rating of 26 for the 1/4″ foam and STC rating of 33 for the 1/2″ foam. It does not have the ratings of a pure soundproofing product and is more expensive–but it also has the foam underlay giving you an all-in-one application. Most standard carpet underlayment does not provide much soundproofing value. It will cushion the floor somewhat and reduce footfall noise. When discussing carpet and underlay with a supplier, I would make sure that the STC and IIC ratings are available to back up any claims made.

 

– STC rating of 66 and IIC rating of 67 (when installed on the floor assembly)

– Moisture barrier, Compression resistant felt, for use over concrete and wood subfloors

– Approved for infloor heating systems and concrete floors

Both the Roberts and the QuietWalk Plus products have adhesive strips on one side to attach them when installing. The Premium Carpet Underlay does not. It has to be butted together and the joints taped. (Note: I would use tape on all 3 products just because I am not a trusting guy.)

Area Rugs

All rugsdampen vibration to some extent. You can use a rug in the middle of the room with a good soundproofing underlayment to quiet footfall noise in high traffic areas. But if your rocking chair is sitting on the laminate or hardwood floor, you are not really solving the problem. Putting down a rug in noise-making, or high traffic areas, will certainly help. Make sure that you use double sided tape to secure the underlay pad to the floor and the rug to the pad. The tape will help with safety and save you from chasing rug and pad around the room every couple of days.

 

 

Best Soundproofing Underlayment for Laminate and Engineered Flooring

These types of floors are becoming more and more popular. They are relatively easy to install, the cost is acceptable (although you should be careful of some of the really cheap product), and most of them look pretty good when installed. 

Roberts Premium Felt Underlayment

• Soundproofing super felt underlayment designed for floating laminate and  engineered wood floors
• Moisture barrier protects flooring from absorbing moisture (Although if you are applying it over concrete–specially relatively fresh concrete–you should give some consideration to first putting down a 6 mil poly vapor barrier to ensure that no moisture gets to the underside of the flooring)
• Absorbs sound
• 3 mm thick pad helps correct minor imperfections in sub-floor
• STC 66, IIC 67 (Rated when part of complete floor/ceiling assembly)

Although this product comes with its own adhesive strip and 2 1/2″ overlap, I would invest in a couple of rolls of tape to ensure the strips stay together and there is a continuous moisture barrier.

 

MP Global QuietWalk Plus

• 94% Recycled Soundproofing material underlayment designed for floating laminate, engineered wood, solid wood, rigid core vinyl floors
• Moisture protection and vapor barrier protects the flooring from harmful moisture (Although if you are applying it over concrete–specially relatively fresh concrete–you should give some consideration to first putting down a 6 mil poly vapor barrier)
• Absorbs sound, no off-gassing 
• Thick enough to help correct minor imperfections in sub-floor
• STC 66, IIC 71 (Rated when part of complete floor/ceiling assembly)
• Can be used with Floating, Double glued down, or Mechanically fastened flooring

Although this product also comes with its tape strip to join sections, I am way too anal to completely trust this. I would certainly invest in a couple of rolls of moisture proof tape to make sure the sections stay together and there is a continuous moisture barrier.

QEP Cork Underlayment

• 85% Recycled soundproofing material underlayment designed for glued-down or floating floor installation of LVT (Luxury Vinyl Tile), VCT (Vinyl Composition Tile), VET (Vinyl Enhanced Tile). Also Sheet Vinyl and Linoleum flooring. 

Note: I hate someone spewing industry jargon like LVT, STC, VET, IIC, etc. at me without some kind of explanation. So I try not to do it.

• Non-absorbent and mold-resistant (although I would use 6 mil poly vapor barrier over concrete and any place you think there might be moisture that could get to your flooring.)
• High density makes it resistant to residual indentation
• STC 55,IIC 55 (Rated when part of complete floor/ceiling assembly)

This product does not come with a tape strip to join sections, so you will have to provide your own tape. Also, it tears quite easily so take care walking on it before the flooring is installed. (Tape any tears you might make.)

 

Best Soundproofing Underlayment for Hardwood Flooring

I love true hardwood floor. Unfortunately, it has a couple of drawbacks when it comes to soundproofing. It is nailed to the sub-floor assembly which will transfer noise through your soundproofing membrane to the floor/ceiling below, causing Structure-borne Noise (Impact Noise). If it is not nailed down properly (or if it is not nailed into 3/4″ plywood–at least) it will become loose and either slide up and down on the nails or rub on the sub-floor–neither of which will make you happy because of the squeaking noise. And from my point of view–if I cannot nail it, screw it down, or glue it down–I am not sure I want it.

For a truly quiet nailed down hardwood floor, you will have to create a floating subfloor. This is particularly true if you are installing hardwood over a concrete floor. (A 2″ long hardwood flooring brad will come out the other side of 3/4″ plywood, so you will need at least double 3/4″ plywood.) The following Duracoustic product will help decouple the existing subfloor (wood or concrete) from the floating plywood subfloor you are going to install and the hardwood. Green Glue installed between the two plywood layers will make the whole system even quieter.

Duracoustic S.T.O.P. 

• manufactured by acousticsurfaces.com
• 5/16″ thick recycled rubber-based soundproofing underlayment bonded to a fiberglass/cellulose backing scrim (an open-weave fabric to keep things together).
• resists mold, mildew, and fungus; works well with infloor radiant heating; will not break down during installation
• acts as sound decoupler for floor/ceiling assemblies and helps prevent Flanking Sound (Designing Buildings Wiki) passing from room to room
• STC 64, IIC 55 (Rated when part of complete floor/ceiling assembly)

DURACOUSTIC S.T.O.P.™

Product Testing & Information

Image Courtesy of Acoustical Surfaces Inc.

MP Global QuietWalk Plus

• 94% Recycled Soundproofing material underlayment designed for floating laminate, engineered wood, solid wood, rigid core vinyl floors
• Moisture protection and vapor barrier protects the flooring from harmful moisture (Although if you are applying it over concrete–specially relatively fresh concrete–you should give some consideration to first putting down a 6 mil poly vapor barrier)
• Absorbs sound, no off-gassing 
• Thick enough to help correct minor imperfections in sub-floor
• STC 66, IIC 71 (Rated when part of complete floor/ceiling assembly)
• Can be used with Floating, Double glued down, or Mechanically fastened flooring

Although this product also comes with its tape strip to join sections, I am way too anal to completely trust this. I would certainly invest in a couple of rolls of moisture proof tape to make sure the sections stay together and there is a continuous moisture barrier.

Best Soundproofing Underlayment for Tile Flooring

Tile flooring requires a solid base because it is glued down. Some of your options and my suggestions follow.

 

Schluter Ditra Stone & Tile Underlayment

• specifically made as underlayment for stone or tile
• meant to be used with another soundproofing underlayment
• works very well as a decoupler but in their own tests (Schluter Systems) the product only raises the IIC by 10 on a concrete floor (IIC 28 to IIC 38 which includes the product, 2 layers of thinset, and the mass of the tile itself)

Note: The only way I can see this working as a soundproof underlayment system is to put down a soundproofing underlayment (any of those described above), then 1/4″ cement board, or 3/8″ Good One Side (G1S) plywood, then the Schluter Ditra (with a layer of thinset on each side), then your tiles. Seems like a lot of effort to me.

 

QuietWalk Plus, Duracoustic, QEP Cork

The option I would choose is to put down any one of the other products I have suggested. Tape the joints as required. (Note: None of these products require much in the way of fasteners. They will lay fairly flat when you put them down.) Now put down 1/4″ cement board, or 3/8″ G1S plywood. Screw, or staple, well (about every 6″ around the edges and 8″ throughout the rest of the sheets). Install thinset, tiles, and grout. The underlayment will give you the good STC and IIC ratings, and the cement board (or plywood), thinset, and tiles will provide mass.

Notes:

• The only drawback to using this system is the fasteners connecting the cement board or plywood in the subfloor assembly. I am willing to put up with the slight increase in Impact Noise and Flanking Noise getting into the adjacent rooms–in exchange for a less costly, and quicker installation. But you will have to decide on your own trade-offs.
• I know of tiles that have lasted for years on a wood underlay with the grout intact. I do now know much about the Schluter Ditra product so I cannot give you a real honest opinion.

 

Best Soundproofing Underlayment for Sheet Vinyl (Linoleum) Flooring

Soundproofing underlayment for sheet vinyl is going to be pretty much the same as ceramic tiles. This stuff needs to be glued down. Sheet vinyl cannot be glued to felt, foam, plastic moisture proofing, or rubber efficiently–if at all. So put down the soundproofing underlayment of your choice (QuietWalk Plus, Duracoustic, Roberts Premium Felt). The biggest difference from tile underlayment is that you should replace cement board with 3/8″ thick particle board. This should be stapled down every 6″ to 8″. (Note: Most particle board used for vinyl underlay comes marked for staples. Use wide crown staples. They hold better and do not chip out as much particle board.)

Notes:

• If you are replacing vinyl flooring with vinyl flooring–do not remove the existing unless absolutely necessary. It is usually a long, painful, and annoying project. Just put down your soundproofing product (I might use thicker QEP Cork–especially if the old floor is in ugly shape) then the particle board, then the sheet vinyl.

 

Final Thoughts

I am sure you noticed that one name shows up fairly regularly for almost all types of flooring. QuietWalk Plus. It is not necessarily the absolute best for every situation but it provides very good ratings and can be used for almost everything. And if you are re-flooring your entire house, or a significant part of the house, you can use it everywhere without worrying about changes in thickness, or buying too much, or buying too little. I have found that sometimes convenience can be more important than having the very best–as long as you do not have to sacrifice too much quality.