Sound Transmission

When it comes to flooring, the more muffled the sound, the better, especially in a multi-story building, house, apartment, or condominium. Fortunately, there are several good flooring choices with effective sound dampening properties.

Sound is transmitted when hard objects, like hard-soled shoes, furniture, dropped objects, or even dog claws impact a hard surface, like tile or stone. Without anything to absorb it, sound waves can spread, multiply, and echo off the walls, amplifying even a small sound to a distracting crescendo with the right acoustics. Given a large room with high ceilings and hard polished floors, a simple walk across the lobby of an office building, for example, can become quite a distraction.

Sound Ratings

Sound transmission is rated using three different standards, each defining a different way in which sound is transmitted. Sound absorption of floor coverings may be measured on two of those scales. The third covers room-to-room transmission, more appropriate for walls.

IIC (impact insulation class) is measured in terms of sound impact, or how well sound vibrations travel through a floor to the room below.

IIC 50 has the least impact sound absorption quality. While this may be appropriate for ground floors, it would be unsatisfactory for most on a high floor without a great deal of insulation in the area between the floor and the ceiling below. Most stone and tile will fall into this category.

IIC 60 indicates a medium impact sound absorption quality and encompasses floorings such as wood, laminates, and some vinyls.

IIC 65 is a high level of impact sound transmission absorption and includes superior sound reduction materials like carpet and cork.

IIC is greatly influenced by the surfaces and areas under the floor and the IIC rating can be significantly enhanced by the addition of underlayment, insulation, or by floating the floor. The “loudest” floor is stone or tile laid directly over concrete. The IIC scale does not account for joist noises like squeaking or rattling.

NRC (noise reduction coefficient) measures the amount of noise that is absorbed by the material and not reflected. A room with a high NRC rating would eliminate background noise and echoes to help clarify speech. Theaters, for example, must be constructed to have a high NRC rating. Without it, sound waves would bounce off the walls and crash into each other, creating a cacophony of continuous sound, making individual words impossible to distinguish. Carpet, with an NRC rating of .40–.50 is the most efficient absorptive material. Vinyl, cork, and rubber have a fairly high NRC rating, with hardwood, bamboo, tile, and stone at the bottom of the scale for sound absorption.

Under the Floor

Sound transmission is affected by more than just the top layer of flooring. Other factors include the underlayment and subfloor, plus adhesives and sealants used during installation. If used on a higher floor in a multi-story structure, insulation between the floor of one room and the ceiling of the room below plays an important part in deadening sound. Any kind of insulation packed between the joists will not only help to trap and dissipate sound, it will block the loss of heat or air-conditioning, effectively lowering your utility bills.

Installation Materials

The use of flexible acoustic adhesives adds yet another layer of sound dampening properties to the floor. Applied around the edges of the floor, a flexible sealant is designed to fill gaps where the floor meets the wall or around doors or air ducts in order to block channels where sound can travel.

Flooring for Sound Reduction

Carpet

Number one on the on all counts is carpeting. By definition, carpet is the antithesis of hard, echoing surfaces. Sound waves are effectively absorbed and deflected by the carpet and by the padding under the carpet, and the level of sound absorption can be enhanced with a thicker pad. Carpet is usually the cheapest option in the short run, but also the most problematic in terms of durability, cleaning, and allergy aggravation because it tends to trap allergens and dust.

Cork

Cork is a great choice for sound reduction. It does more than merely dampen sound; it absorbs it, creating a blissful peace that everyone will appreciate, including downstairs neighbors. Cork is such an effective sound reduction material that it is used on walls to soundproof recording studios to produce clear soundtracks without background noise. The key is in the porous structure of the cork. Rather than bounce around, sound waves sink into the cellular structure of the cork and are broken up.

In addition to the obvious benefit of sound reduction, cork flooring adds natural warmth to rooms and a slightly springy give that makes it comfortable and easy to walk or stand on and may even save dropped objects from breaking on impact.

Vinyl

Quality vinyl flooring that is backed with foam and has a cushioned, flexible surface, makes it a good choice for a sound reduction, but as with everything else, you get what you pay for. While you can install any tile over an existing floor, the material of the floor will influence sound absorption qualities. Top quality vinyl will help nullify that factor and provide a nearly soundless surface that has spring and give for comfort.

Laminate

Laminate flooring can be a reasonably good choice for sound reduction with the addition of a quality underlayment. In addition to absorbing sound, a layer underlayment will add a feeling of solidity to the floor and reduce the hollow percussive sound that footfalls can produce when laminate flooring is floated over a subfloor without the benefit of underlayment. The underlayment pads a laminate floor much in the same way that a pad works under carpet, adding give for extra comfort and insulation for overall warmth.