Batts of mineral wool insulation stacked together

Mineral wool (also known as Rockwool) is one of the most common insulating materials currently used in the US and Canada. It is made from natural rock and steel slag, a recycled by-product of steel production. 

If you are planning to insulate your living space, be it a new house or simply an old one in need of an upgrade, you should learn as much as you can about mineral wool, as it is one of the most popular insulating materials currently available. 

Rockwool insulation offers several advantages, such as excellent performance in terms of both thermal and noise insulation. It is also quite durable and resistant to fire, mold, mildew, etc.

The only disadvantages of Rockwool are that it is not biodegradable and can be slightly more expensive than similar insulating materials like fiberglass and cellulose. 

This article will take a deeper look at this insulating material, including its origins, manufacturing process, and weigh its pros and cons. It should help you decide whether or not mineral wool insulation is suitable for your home. 

What is Mineral Wool Insulation?

Mineral wool insulation is typically made from volcanic rocks such as basalt, dolomite, or diabase. It also contains some recycled materials such as steel slag and iron-ore waste. 

Hence, mineral wool is made almost entirely from raw materials that are recyclable, natural, and renewable. 

Thousands of tons worth of slag is produced every year by the iron ore and steel industries. Typically, this waste material is sent off to landfills to clog the earth’s surface for centuries to come. 

The manufacturing process of mineral wool turns this waste material into effective and high-performing insulation. It makes excellent use of industrial waste that wouldn’t otherwise have been used for anything productive. 

Volcanic rocks are the other component of mineral wool. As you probably know, rocks and stones are natural resources that are almost inexhaustible in quantity. Igneous or volcanic rocks form more than 15 percent of the planet’s entire land surface. 

Hence, all the materials used to manufacture Rockwool insulation are eco-friendly and sustainable. In addition, the minuscule waste generated during the manufacturing process of mineral wool has earned it an “A” rating from the BRE Group’s Green Guide to Specification.  

This insulation material is also very versatile. It can be used to insulate every part of a home, including the roof, walls, and floors. Mineral wool is also sometimes used to insulate the attic, although this application is rarer than the others. 

Mineral wool generally comes in two forms—loose-fill and batt insulation. The type of mineral wool insulation that is right for you will depend on the specific application, your budget, the kind of house you have, among other factors. 

The thermal performance of mineral wool is quite impressive. For example, rockwool batts made for traditional 2×4 walls have an average R-value of 15 or higher.

A worker lifts a batt of rockwool insulation off a stack as he readies it to be applied to an attic ceiling

On the other hand, the batts made for 2×6 stud walls have an R-value of 23, which is significantly higher than the R-values of comparable insulation materials like fiberglass. 

Click here to learn more about the R-value of Rockwool insulation.

Loose-fill Rockwool is not far behind, offering an R-value of 3.0 to 3.3 per inch of thickness. This enhanced thermal performance can be attributed mainly to the unique manufacturing process of mineral wool insulation. 

The Manufacturing Process of Mineral Wool

The mineral wool manufacturing process is unique and exciting. This insulating material was first invented more than 150 years ago when an erupting volcano made onlookers realize that strong winds could whip volcanic lava into wooly tufts. 

Soon, scientists found a way to replicate this natural process in factories to produce mineral wool for insulation.

Batts of mineral wool are typically tucked between a framed wall’s studs to maximize thermal and acoustic insulation.

Basalt rock, steel slag, dolomite, oil, and various resins are used during the manufacturing process. The entire operation is fueled by coke, a type of distilled coal. 

Basalt rock is formed when rock melts into lava due to volcanic activity. This lava later cools down again, creating rock known as basalt.

The basalt rock is crushed at the quarry, then liquified into the lava in a furnace at temperatures exceeding 1,600ºC to make Rockwool.

Mineral wool manufacturers typically use a cupola furnace, but other gas or electric furnaces can also be used, including chamber, cyclone, and shaft furnaces. 

This liquified basalt rock is then poured into a special spinning machine and spun into long, thin strands of Rockwool. This process has often been likened to a cotton candy machine spinning melted sugar into the fine, fluffy substance sold to kids at carnivals.

A binding solution made from oils and resins holds these strands of rock fiber together and acts as an effective water repellant. 

Machines at the factory then layer the fleecy webs of newly-made Rockwool over one another in a zigzag pattern. The number of layers will vary, depending on the type of insulation product being manufactured.

Rollers are then used to compress these layers of Rockwool and add density to the material. The compressed Rockwool then enters an oven, where the heat helps solidify the binders applied earlier, ensuring that the insulating material will hold its shape. 

An end-facing view of a roll of mineral wool insulation

Finally, the mass of newly-made Rockwool insulation is cut into smaller batts for packaging. Before being released on the market, the manufactured mineral wool is usually tested extensively to ensure high resistance to heat, fire, moisture, etc. 

The Pros and Cons of Mineral Wool

The reason for the popularity of mineral wool insulation is that it comes with a wide range of practical and environmental benefits. However, like every other consumer product, it is not for everyone. 

It does have certain drawbacks, which may or may not affect you, depending on your priorities and circumstances. But you should know about what they are to make more informed decisions about your living space. 

Advantages of Rockwool Insulation

Energy Efficiency

The high R-value of mineral wool insulation ensures that it is incredibly energy efficient. 

It is said that the energy used to produce mineral wool insulation can be recovered within five months of its installation within the home. Click here to learn about the different governmental energy efficiency programs for your home. 

In other words, within five months of being installed in your living space, mineral wool insulation will save as much energy (in reduced heating and cooling requirements) as was used to manufacture the material in the first place. So, any energy savings after the five-month mark is just a bonus!

Durability 

Made from tough and durable raw materials like steel slag and igneous rock, it is no wonder that mineral wool insulation offers exceptional longevity. Moreover, this material is not prone to sagging and settling, which means its R-value remains unchanged over time. 

Another reason for the relative durability of mineral wool is that, although it’s packed together very tightly, the stone fibers within a batt have natural air pockets, keeping the material breathable and preventing moisture buildup. 

Furthermore, the melting of basalt rock at temperatures exceeding 1,600ºC effectively eliminates any organic material. The lack of organic material in Rockwool insulation, in turn, prevents the growth of mold, mildew, and fungus, helping enhance the longevity of the material.  

Fire Safety

Because of the way it is manufactured (in a furnace where temperatures are high enough to melt rock and steel residue), mineral wool is incredibly resistant to heat. 

It is non-combustible and can easily withstand temperatures up to 1,000ºC. Not only does it not catch fire, mineral wool insulation also does not release smoke or toxic gases when exposed to flames and high heat. 

Therefore, mineral wool is often used as a fire barrier between different floors of a house, or between different houses in a neighborhood. It can help slow the spread of fire and give the fire services more time to get the situation under control, potentially saving many lives.  

Soundproofing

Mineral wool insulation is perfect for bedrooms, media rooms, and any other part of the house where noise reduction is a priority. This insulating material slows down (and traps) the sound waves as they pass through it. 

Thus, it is a popular insulating material used in multifamily residences and single-family homes located in noisy areas. The high density of Rockwool batts makes them effective at noise reduction. 

Easy to Install

As an insulating material, mineral wool is exceptionally dense and rigid, making it easier to install than many other types of insulation. The greater rigidity of this material ensures that it can be cut more precisely, allowing for very accurate trimming around electrical outlets and other obstructions. 

Close-up of worker hands in white gloves installing mineral wool insulation staff in wooden frame for future walls for cold barrier.

Mineral wool insulation also offers great flexibility in how it can be used and installed. For example, it may be purchased in rolls or batts that can be cut into various shapes and sizes, as required. 

To better insulate your walls, you can also buy Rockwool that has been compressed into rigid boards, making the material easier to install. Lastly, loose-fill Rockwool can be used to insulate attics and ceilings efficiently. 

Disadvantages of Rockwool Insulation

Health Risks

The tiny slivers and fibers of mineral wool insulation can be easily accidentally inhaled or ingested during installation. These stone fibers can also become embedded in the skin, causing rashes, itchiness, and general skin irritation. 

If inhaled, the tiny fibers of mineral wool can potentially irritate the alveoli and cause various lung problems. Therefore, it is good to wear gloves, goggles, a dust mask, a long-sleeved shirt, and other types of protective gear when installing mineral wool insulation.  

Cost

Mineral wool insulation is more expensive than other comparable materials, like cellulose and fiberglass, partly because of its state-of-the-art manufacturing process, which uses powerful furnaces, spinning chambers, and other expensive pieces of technology.

As a result, mineral wool can often be as much as 25 percent costlier than other similar insulation materials. It is also less readily available than fiberglass insulation, and the range of available sizes is not as comprehensive.  

Extra Weight

Made from molten rock and steel slag, mineral wool is denser than most other insulation materials. Howbeit, while this enhanced density has its advantages, it also has the side-effect of making mineral wool insulation unduly heavy. 

The greater weight makes mineral wool harder to handle during ceiling and roof installations. In addition, more manpower is required to install the heavier material, making the entire process more expensive.

If you’re trying to do a DIY installation, the additional weight might also increase the risk of an accident. 

Furthermore, the dense nature of Rockwool makes it harder to cut the batts to size. A unique wood saw, or serrated knife might be required for this purpose.

These are some reasons why mineral wool is rarely used for attic insulation. 

A Brief Overview of the Pros and Cons

Mineral Wool/Rockwool Insulation
ProsCons
Made from recycled and renewable materials. Requires an extensive manufacturing process, which drives up the price.
It is dense and rigid, making it easier to make precise cuts.The extreme density of Rockwool makes it heavy and unwieldy. 
Made from molten rock and steel residue, mineral wool is very tough and durable. The rock fibers can get embedded in the skin during installation, causing rashes and itchiness. 
Old and discarded mineral wool can be recycled to form new insulation products.Rockwool is not biodegradable, which reduces its environmental benefits. 

Finishing Thoughts

As you can see, mineral wool insulation has a wide range of benefits, as well as some drawbacks. To determine whether this insulation material is suitable for your home, you should seek the advice of professional insulation technicians, architects, and other homeowners who have previously installed Rockwool insulation in their houses. 

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