7 Things to Know About Rockwool Insulation Before Installing It in Your Home

Ensure you enjoy the full benefits of Rockwool by learning about the creation, composition, and features of this insulation.

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Fiberglass insulation has long been a popular option for slowing the transmission of heat through the walls and ceilings of a home. While it may have the added benefit of creating a fire-resistant layer between the interior and exterior walls, fiberglass still may not measure up to the natural abilities of Rockwool. Like fiberglass, Rockwool is an insulation material that is regularly used in residential, commercial, and industrial buildings.

However, Rockwool can be differentiated from fiberglass by comparing the heat retention, fire resistance, moisture resistance, and soundproofing capabilities. Keep reading to find out more about Rockwool insulation.

1. Rockwool is made of rocks heated to become lava-like liquid.

The process by which Rockwool insulation is made helps to explain the true fire-resistant potential of this product. It’s composed primarily of basalt rock and a recycled steel-making byproduct known as slag. These components are superheated, allowing them to liquefy and mix together into a lava-like liquid. In order to melt these substances, the temperatures must exceed 2,900 degrees Fahrenheit.

The mixture is then blown into a large spinning chamber designed to stretch the superheated liquid into fibers. These fibers are then gathered together and compressed into a mat, which can be cut into slabs of Rockwool insulation.

By creating Rockwool through this process, all organic matter is eliminated, greatly increasing the mold- and mildew-resistance of the finished product.

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2. It contains between 16 to 75 percent recycled material.

The confusion about the amount of recycled material used to make Rockwool insulation can mostly be attributed to the statistics about mineral wool insulation in general. Rockwool is a brand-specific type of mineral wool insulation that is so popular the name became synonymous with the appropriate term, which is mineral wool. The brand-specific Rockwool insulation is typically made of between 16 to 40 percent recycled materials, according to the manufacturer. However, the U.S. Department of Energy has stated mineral wool insulation contains an average of 75 percent of recycled materials.

This estimate is hard to back up because the Department of Energy makes the distinction between standard ‘rock wool’ insulation and ‘slag wool’ insulation, but doesn’t note the difference in the amount of recycled material for each product. Also, this is a perfect example of the ‘Rockwool’ brand name being used in place of the generic material name, blurring the lines between products.

In general, it can be derived that the amount of recycled material in Rockwool insulation is not precise because it ultimately depends on the specific product. Standard Rockwool insulation may only have between 16 to 40 percent recycled material, while slag Rockwool insulation can be made with up to 75 percent recycled material.

3. Rockwool has excellent heat retention.

Both fiberglass and Rockwool are effective at keeping a home cool in the summer and warm in the winter, but the specific thermal efficiency of these materials favors Rockwool. While fiberglass insulation is capable of offering an R-value of about 2.2 to 2.7 per inch of insulation, Rockwool has an R-value between 3.0 to 3.3 per inch of insulation.

Fiberglass insulation also tends to lose its thermal efficiency over several years as it begins to degrade. Due to the method of construction and the materials used to make Rockwool insulation, the thermal performance of this insulation remains stable over the lifetime of the building. However, Rockwool tends to cost more per square foot than fiberglass insulation.

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4. The material is fire-resistant up to 1,400 degrees Fahrenheit.

As noted previously, Rockwool insulation is formed from literal rocks and steel slag that must be heated beyond 2,900 degrees Fahrenheit in order to mix the component materials and create this highly effective insulation. With this in mind, it makes sense that mineral wool products in general can resist fire, flames, and heat up to 1,400 degrees Fahrenheit, while some Rockwool products are capable of resisting temperatures up to 2,150 degrees Fahrenheit without melting, smoking, or catching on fire.

This impressive heat-resistance is ideal for building homes because the insulation forms a fire-resistant barrier between the interior and exterior of the home, between rooms, and even between floors, slowing the spread of fire. It should be noted that fiberglass insulation is also highly heat-resistant, though it begins to melt at about 1,100 degrees Fahrenheit.

5. Rockwool is a highly durable insulation option.

The durability of this insulation material is difficult to dispute, given that it is capable of retaining its thermal efficiency over several decades with minimal degradation in its R-value. This is primarily due to the materials used to make Rockwool insulation, including rock and steel slag, which are known for having a high level of durability and natural resistance to decay and corrosion.

However, the durability of Rockwool isn’t limited to the heat retention quality of the material. The impressive water-resistance, mold-resistance, mildew-resistance, and fire-resistance also contribute to the durability and capability of Rockwool insulation. This is especially true of the material’s moisture-resistant qualities, without which the insulation could absorb and retain water from highly humid air, causing the premature breakdown of the material.

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6. Rockwool insulation is great for soundproofing rooms.

Some people may not appreciate the heftiness of Rockwool insulation because it does tend to be thicker than fiberglass insulation, but this helps to slow the transmission of heat and it has the added effect of slowing sound waves. As sound waves attempt to move through the material, they are slowed and sometimes completely blocked, creating built-in soundproofing.

While the thickness of the insulation helps to block noise, it is the density of Rockwool insulation that provides the soundproofing. Fiberglass insulation has a density of about 0.5 to 1.0 pounds per cubic foot, allowing it to reduce sound by 4 to 10 decibels. Rockwool insulation has a density of around 1.7 pounds per cubic foot, which is capable of consistently dampening sound by 10 to 15 decibels.

7. Rockwool allows moisture to escape and prevents the growth of mold.

The construction and composition of Rockwool makes it ideal for rooms that are prone to high levels of humidity, like the bathroom or kitchen. Rockwool insulation’s moisture-resistant and vapor-permeable qualities mean that any liquid water will drain away from the insulation instead of soaking into it, while gaseous water vapor will pass through without dampening the material.

Additionally, Rockwool insulation is inorganic, so it makes a poor medium for mold and mildew to grow as there is nothing for them to use for energy. In fact, Rockwool products are also tested and certified as resistant to fungal growth, reducing the chance that users will open up the wall and find a dangerous biological problem waiting for them.