The Truth About Sound Control Underlayment

Property Managers have to be knowledgeable about a wide variety of issues to do with building systems and materials. Combine that with the challenging personalities you have to deal with and it’s surprising that you can convince anyone to become a Property Manager! It’s especially difficult when you are dealing in an area where there is so much misinformation. The ‘Sound Control Underlayment’ market is one of those places where wild performance claims abound yet solid testing information is scarce. So what is a Property Manager to do? Be skeptical & educate yourself. The purpose of this blog is to help Property Managers ask the right questions and gather the information required to make an educated decision about Sound Control Underlayment. It’s vital that any Property Management Company not only to protect their reputation, but also demonstrate due diligence and potentially shield them from legal issues


Sound Control Underlayment is being specified in condominiums and multifamily housing to keep the peace and allow the ‘quiet enjoyment’ of each resident’s suite. They must, when new, perform according to product claims; they also must not cause issues in the future. So where to start? Ask the right questions:

• How was the product tested? On what building assembly? If it’s not clear in the literature, demand to see the test report.
• Does it meet the IIC requirement of this building? What is a ‘reasonable’ requirement for the ‘financial demographic’ of your building?
• What is the product made of? Really important for downstream problems. What will happen as this product ages? Will it harden, crush, dry out, absorb or wick?

They seem like pretty simple questions right? They are not! Many manufacturers of underlayment are betting on the fact that PMs are not Acoustic Engineers and will scan the sales literature for the highest Impact Insulation Class (IIC) rating, approve it, and get on with their day. Millions of square feet of sub-standard underlayment have been installed, leaving desperate residents, dangerous neighbour animosity, frustrated PMs and management boards and ‘no win’ legal situations. Let’s look at each of those questions to understand what they truly mean.

1. How was the product tested?
The first red flag for a PM is product literature or packaging that shows an IIC rating but does not indicate the building assembly that it was tested on. This is by far the most common ruse. The producer of the literature is banking on keeping the PM or general public in the dark about what IIC means. Higher is better right? This is where the field runs from truthful to deliberately misleading. If the indicated IIC ratings are in the high 60s or 70s and do not show the assembly – RED FLAG! But what does IIC mean and how can a PM understand and apply this rating? IIC is Impact Insulation Class. Predominantly it means how well one underlay or another reduces the sound of footfall, chair drag, or spoon drop, etc. Learn about IIC and its implications here.

• One issue is how the paper’s author is allowed to report the product testing. The testing is always done on new (fluffy) material. There is no requirement to ‘put a book case on it’ and come back in six months and test it then – to see if the material has crushed out. That’s what happens in real life and why the acoustic performance of so much acoustic underlayment degrades so quickly.

• The second thing that should throw up red flags for a PM is the inclusion of a Sound Transmission Class (STC) rating in the product literature or packaging. Airborne sound only respects mass or separated mass. That thin piece of rubber, foam, cork or felt has nothing to do with increasing or decreasing the STC rating. Higher is better but it’s only relevant if they tell you what the whole assembly is. Different underlayment only influences STC ratings by a miniscule amount; underlayment has almost no mass.

• It should be noted that unless specifically requested by the flooring manufacturer, vapour barriers are not required for installations on cured concrete above grade.

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2. Does it meet the IIC requirement of this building?

What is a reasonable requirement for the financial demographics of your building?

• This is a question that must be answered by the board of directors in conjunction with information the PM or consultant brings to the table. Different buildings have different financial demographics. Asking a resident who can only afford $0.99 laminate to buy a $3.00 per sq. ft. underlayment may be unreasonable. But in an upscale building the residents and board will expect/demand that the property management company does not allow their building to ‘go bad’ by allowing underperforming underlayment. This class of owner does not want ensuing noise complaints or a reputation that could devalue the property. Here a $ 3.00 underlayment may be a reasonable request.

• Nearly all reported IIC ratings will be with a wood floor finish of some kind. An 8” concrete slab on its own will typically have an IIC from 32-36. Low-end underlayment can provide a Delta IIC (improvement) of 18-19 points, bringing the assembly to 50-55 IIC. This is the low end of where you would want to be – but it may be all that is feasible for certain buildings. High-end underlayment can provide a Delta IIC of 21-32 points yielding assemblies that range from 53-68. That is all that can be expected on an 8” slab with no drop ceiling. A tile installation will be at least 5-8 points below this. Understanding this allows us to realize that IIC claims going beyond 70 should be regarded with suspicion.

3. What is the product made of?

What will happen as this product ages? Will it harden, crush, dry out, absorb or wick?

• It really does make a huge difference what it’s made of.

• Underlayment in general is made of, cork, foam, rubber or felt. Below is a breakdown of each underlayment and there performance:

• CORK – The Granddaddy of underlayment. This is the material that has been grandfathered forever, because it’s been around forever. On a 6” concrete slab with a wood floor and 5 mm cork you’ll get approximately a 50 IIC. On an 8” slab it could get up to 55 IIC. Cork is kind of a known commodity but has some downstream issues that should be considered. Cork is, as we know, bark off a tree. Let’s look at a product we all know and love for an example of its performance – wine! Wine corks are top quality because they protect precious cargo. Now, mentally pull the cork out of your favourite two-year-old bottle. The end of the cork that was next to the wine is still soft and pliable. What’s the other end like? It’s compressed, hard, dry and showing signs of getting flaky. That’s because it was exposed to the air. The same happens with the thin layer of cork under flooring. It dries, gets harder and flakes out – along with it goes the acoustic properties we needed to begin with.

• FOAM – Foam does a reasonable job of taking up any minor irregularities in the subfloor and they do take away some of the ‘clacky’ sound laminate can have as you walk on it. When foam is new and ‘fluffy’ it exhibits some reasonable sound control properties. But there’s a problem. The problem is foam cannot withstand ongoing loads. It eventually crushes out and along with that physical deformation goes the sound control properties that we need. Many foam products available today are re-purposed packaging material; foam gained a foothold on the underlayment market because it’s cheap. But you get what you pay for in the sound control department here. Here’s a really easy test any PM can do. Take any underlayment and put it under the corner of your desk or a chair leg for a few days. Then take it out, let it recover for a few minutes then look at it and feel it. Did it permanently deform? It will do the same over time under the flooring in that suite.

• RUBBER – Rubber underlayment is becoming the new Granddaddy on the market. In Europe and North America, it is being made by companies that used to manufacture cork. Rubber exhibits superior sound control properties, strength and aging characteristics that make it particularly suitable for sound control underlayment. Made from strong, recycled tires, rubber cannot be crushed out. This underlayment can be grossly overloaded but recover completely when the load is removed. It is timeless in that they will never have to be replaced in the lifetime of the building. Rubber tends to be a bit more expensive than the contractor grade of foam underlayment, but it’s worth it.

• FELT – Felt underlayment exhibits good sound control properties and generally good aging characteristics. It does a great job with sound control, but again there are downstream issues that could become a big problem. A wood or laminate floor is actually a collection of pieces with spaces in between that narrow and widen with the seasons as the materials react to the humidity levels. This is natural. While felt exhibits good sound control and support characteristics, it also allows liquid to ‘wick’ laterally under the flooring. Once this happens, the floor fails. What are the chances that a floor will experience a spill in its lifetime? Probably 100 percent. If a felted underlay is used and a spill occurs, resulting in floor failure, who’s responsible?

The Questions to Ask:
Here’s the questions you need to come armed with when investigating any acoustic underlayment.

1. Has the PM, board of directors and even an outside third party consultant set up reasonable, realistic IIC criteria for the building(s) in question? Do so.
2. Does the underlayment literature clearly show the building assembly that is was tested on? If not, request the test data. If it is forthcoming, does it match this buildings construction?
3. Finally: what is it made of? Will it harden or dry out over time? Will the material crush out over time? Will it wick liquid laterally under the flooring if exposed to a spill? Does it pass the ‘desk test’?

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