Best Attic Insulation for Soundproofing

Are you on the hunt for some peace and quiet in your home? Do you have kids in search of a place to take up noisy hobbies without disturbing the entire family? These are just some of the many appealing and practical reasons to consider insulating your attic for soundproofing purposes.

From fiberglass to spray foam, there are many options with attic insulation. However, the best choice for soundproofing is rockwool. This is also the product we use when installing insulation. Out of all types of attic insulation available today, mineral or rockwool has the best soundproofing qualities when it’s installed properly. Keep reading to get the loud and clear facts on attic soundproofing and insulation.

Sound and Noise Reduction – What You Need to Know

When you think about sound levels, the word “decibels” probably comes to mind. Decibels (dB) are a standard way to measure how loud something is. Using this scale, sound at 130dB typically causes physical pain. Quieter homes, however, usually register somewhere around 40dB. When it comes to measuring how sound resistant a particular type of insulating material is, this is done with Sound Transmission Class (STC).

STC Explained

Introduced in 1961, Sound Transmission Class (STC) is a measurement of how effective a certain type of insulation is at reducing the transmission of sound between areas of a home or room. In the case of an attic, this would be the transmission of sound between an attic’s floor or walls and any spaces around this part of the home.

STC does take decibels into account. In fact, it’s measured by considering the decibel noise reduction a certain insulating material can provide. In other words, STC measures how much noise a particular insulating material will keep from getting into or out of a certain space. This is done by looking at transmission loss, which refers to the volume difference between both sides of a wall or similar barrier.

Generally, the higher an insulating material’s STC rating is, the more effective it is at blocking sound. This determination is based on common frequencies humans can detect – 125 Hz to 4000Hz. Specifically, STC is calculated by evaluating transmission loss values at 18 of the common human-detectable frequencies. What this does is create a curve that can be compared to a standard STC reference curve.


Let’s say the curve created for your attic wall matches the standard STC curve of 40 when the comparison is done. If this is the case, the STC would be 40.

Mineral Wool (Rockwool)

Rock wool is so-named because it’s made of rock-based mineral fiber. It’s common for mineral wool to be made of basal or volcanic rock. It can also be combined with “industrial waste,” or slag, which is created as a byproduct of steel and copper production. These materials are melted at very high temperatures and spun into fibers. The final product is insulation available in the form of pre-cut pieces, or batts.

Rockwool’s R-Value

R-value is a measure of an insulating material’s resistance to thermal transfer – or how well it blocks heat flow in either direction. This has nothing to do with sound, but it’s an important factor. After all, most people want an attic that’s also comfortable and energy efficient in addition to being soundproof. Rockwool has an R-value that ranges from 3.0 to 3.3 per inch. Fiberglass, for the sake of comparison, has an R-value range from .2 to 2.7 per inch.

The Sound Transmission Class of Rockwool

Rockwool has an STC rating that can get as high 56 when it’s used on interior walls, like ones in an attic. The STC rating can vary slightly depending on the manufacturer and the specific materials used in the mineral wool insulation you are using.

The Types of Soundproofing Provided by Rockwool

What makes mineral wool a good choice for soundproofing an attic is its ability to block waves produced by different sound sources. Rockwool primarily blocks two types of sound:

  • Airborne sounds
  • Impact sounds

Airborne Sounds

Airborne sounds are so-named because sounds of this nature are transmitted through air and the atmosphere. These are the kind of sounds generated by things like a TV, people talking, or a dog barking. The resulting sound waves go through the air until they hit a solid barrier. In this case, that would an attic floor or wall. The vibrations go through the structure and radiate through to the other side. The sound that comes through is heard at a reduced volume. The goal with soundproofing is to prevent these vibrations from entirely coming through.

Impact Sounds

Impact sounds are sounds generated by some type of impact on solid materials. The impact generates sound waves that produce vibrations and sounds you can hear. These are sounds you might hear from someone walking up stairs or if someone slams a door, drops something heavy on the floor, or moves furniture in another part of your home. It’s actually impact sounds that tend to be more difficult to isolate. This is because vibrations are stronger and capable of traveling further through solid or dense materials.

Most people hear a combination of airborne and impact sounds on a fairly regular basis. The extent of these sounds can vary, but it can be distracting if you are trying to concentrate or focus on a particular task. By soundproofing your attic with the right type of insulation, however, you can enjoy a welcome break from distracting airborne and impact sounds – but don’t forget about air sealing, which is discussed below.

Air Sealing

As mentioned above, sound waves can travel through air, so air sealing is another step you’ll want to take to boost the soundproofing capabilities of rockwool. “Air sealing” refers to filling any cracks or gaps in your attic before you apply rockwool insulation batts. This can be done by using closed-cell spray foam insulation before installing mineral wool. Closed-cell spray foam has a high R-value, and it’s good at expanding to fill gaps or crevices for added air blockage.