How Thick Is Mineral Wool Insulation?

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There are lots of reasons to be interested in mineral wool insulation. Whether you're trying to avoid VOCs or find something easier to install, mineral wool might keep coming up as an answer. But you still need to be sure it can do the heavy lifting as insulation. So just how thick is mineral wool insulation? We've checked the manufacturer's specs for all the details!

Mineral wool insulation comes in varying thicknesses. The thicker it is, the higher the R-value. You can find anything from R-10 to R-30 mineral wool insulation. R-10 insulation is around 2 inches thick. Higher insulation values can be more like 7 inches thick.

Keep reading to learn more. We'll break down the standard sizes and R-values of mineral wool insulation. Next, we'll explain what makes mineral wool insulation different from fiberglass. Finally, we'll cover what you need to know about vapor barriers and mold and more. Read on to learn everything you need to consider to decide if mineral wool insulation is right for you.

mineral rock wool insulation, How Thick Is Mineral Wool Insulation?

What Is The R Value Of Mineral Wool Insulation?

Like fiberglass insulation, the R-value of mineral wool varies with thickness. In a 2x4 space, you can fit a 3.5-inch thick bat of insulation. This has an R-value of 15.

Meanwhile, a 2x6 stud space fits R-23 insulation. This is 5.5 inches thick.

You can find higher R-values such as R-24, typically 6 inches thick. There's also R-30, around 7.1 inches thick. However, these won't fit in the average wall cavity. As a result, they're used less often and harder to find.

Mineral wool has better insulating properties than fiberglass. In the same 2x4 space, fiberglass insulation rates between R-11 to R-13. In a 2x6 space, fiberglass will offer an R-value of about 21.

Difference Between Fiberglass And Mineral Wool?

Technician spraying blown Fiberglass Insulation between Attic Trusses

Mineral wool may be something you have little experience with. It just hasn't taken off in certain climates and regions. However, the popularity has been growing lately. Mineral wool does have some benefits over fiberglass. These include:

  • Easier to install. Mineral wool is solid, similar to foam board. You can install it into a gap. Once it is fitted, it will just stay. This isn't possible with fiberglass. Fiberglass sort of crumples and has no real form.
  • Fire safety. Mineral wool has a higher fire rating. This makes it a great choice in areas where prolonged fire resistance is necessary. Fiberglass melts at around 540 degrees Celsius. Many kinds of mineral wool can take temperatures of 800 degrees or greater.
  • Better air quality. Fiberglass insulation may leak VOCs, which compromises indoor air quality. Mineral wool is typically a low or zero VOC product.
  • Sound absorption. Mineral wool is thick and dense. It's three times denser than fiberglass. As a result, it helps to absorb sound better. Fiberglass offers no sound deadening properties.

Worker laying out mineral wool in the attic of the house, Can Mineral Wool Insulation Be Left Exposed?

Is Mineral Wool Toxic?

According to the EPA, there's probably low risk from mineral wool - after installation, that is.

Studies show that prolonged exposure to mineral wool is likely nontoxic. Even workers who regularly handle it do not seem prone to health defects. However, the installation of mineral wool is a different story.

During installation, fibers can enter the respiratory system. These are irritating and potentially carcinogenic. Studies aren't clear yet on the damage. If you're installing mineral wool, take the proper precautions to protect yourself.

It's essential to keep airborne particles out of your lungs. Wear gloves, masks, and adequate eyewear. This isn't just because of the air particles.

Some mineral wool is made from toxic materials. An example is formaldehyde. Look for an option with a GREENGuard Certification label. This will ensure you aren't exposed to toxins or off-gassing.

Is Mineral Wool Green?

The problem with what is or isn't "green" is that it's a relative term. There's an argument to be made that mineral wool is green. But other people disagree.

The manufacturing process is not particularly green. The process is energy-intensive, and it can use some questionable chemicals. Formaldehyde can be a part of the manufacturing process. That's not exactly green, by most people's standards.

So the making of mineral wool might not be particularly green. But once it's been manufactured, it lasts a long time. The Rockwool company claims their product lasts the lifetime of the building.

It doesn't require extra chemicals or sprays. Many other insulations need chemicals to prevent mold or be treated to be fire-resistant.

It also uses a lot of recycled materials. On average, mineral wool is 70% recycled. Some kinds, like Thermafiber, are 90%. Fiberglass does recycle glass. But it's only about 30% recycled content.

Because of these variables,  you'll see mixed opinions on whether or not mineral wool can be considered "green."

Does Mineral Wool Mold?

House insulation concept. Roll with mineral rockwool lying on attic floor inside house under construction

Mineral wool comes in unfaced batts, and there is no special vapor retarder attached. This is different than fiberglass, which comes with the facing joined.

This is because mineral wool doesn't need to stay dry to avoid mold. Mineral wool doesn't mold.

Mineral wool repels water. It won't stay wet the way that fiberglass does. Water rolls right off the surface of mineral wool. Mineral wool is hydrophobic.

Fiberglass, on the other hand, absorbs water. Too much moisture can ruin your insulation altogether. Mineral wool wins where moisture is a concern.

Does Mineral Wool Insulation Need A Vapor Barrier?

Mineral wool insulation may come without a vapor barrier. But that doesn't necessarily mean that you won't need one. Mineral wool is hydrophobic and repels water. However, a vapor barrier doesn't exist just for the sake of insulation.

Fiberglass insulation often has a vapor barrier attached. This isn't for the insulation. It's for the entire surface inside the wall.

Mold isn't a problem specific to insulation. Mineral wool may be unlikely to mold. But mold can still grow in the wall.

It can attach to wood or drywall. These surfaces are prone to mold if moisture isn't managed. The enclosed space in the wall gets minimal airflow. This means you have to keep moisture out. The best method for that is a vapor barrier.

What Is The Difference Between Rockwool And Mineral Wool Insulation?

A man rolling mineral rockwool insulation on the attic, Can You Put New Attic Insulation Over Old?

Rockwool insulation is a brand-specific kind of mineral wool insulation. Many companies make mineral wool insulation. Technically, Rockwool insulation refers to the brand of insulation made by the Rockwool company.

It gets a bit confusing when the Rockwool brand is so popular that the name has taken over. It's now commonplace as another word for mineral wool insulation. They refer to generic mineral wool insulation as Rockwool. But it's only, truly, Rockwool if it comes from the Rockwool company.

In a way, it's a lot like Kleenex. While people use the word Kleenex for all sorts of generic tissues, it's inaccurate. Kleenex refers to tissues made by the Kleenex company. Similarly, Rockwool refers to mineral wool sold by the Rockwool company.

Even more complex? While Rockwool is a brand, rock mineral wool is another name for stone wool. Glass wool, stone wool, and ceramic fiber wool are types of mineral wool. The terms refer to the manufacturing process and materials used.

Stone wool is the more common name. It's clearer and less confusing, but different companies use different labels. To differentiate from Rockwool the company, you might see it as rock stone wool, stone wool, rock mineral wool, or another similar combination.

In Conclusion

Mineral wool insulation is a durable and sturdy material that is highly efficient as an insulator. You can find it with an R-value from R-10 to R-30. Standard sizes for a 2x4 space have a rating of R-15. In a 2x6 cavity, expect an R-23 value.

Mineral wool is also better for sound absorption. It's waterproof and less likely to mold. Plus, it's long-lasting and doesn't decay. For this reason, it may be the best insulation for you.

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