Rockwool Insulation: Your Complete Guide

Rockwool insulation is a type of insulation made in an extraordinary way. Most people know very little about this amazing building material. But you don’t need to learn much to know fascinating it can be.

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This type of insulation is used quite often in many areas and is extremely durable. Today, we’re going to learn all that we can about rockwool insulation and everything it is used for. Perhaps you can learn something useful. 

What Is Rockwool Insulation? 

Rockwool is a material that you may often see called mineral wool. This material isn’t wool made from sheep’s wool, but rather, it is made from rocks. This sounds like a phenomenon and in a way, it is! 

Real rocks are heated to around 3,000 degrees Fahrenheit to the point of liquefaction. When melted, the rocks look like magma and are pressurized before being spun quickly to create long strands.

So it ends up looking like cotton or fiberglass insulation but it is in fact made of rocks. But in this case, the rocks are spread very thin. This doesn’t mean they are no longer as “hard as a rock,” making for very durable insulation. 

Why Use Rockwool Insulation

Why Use Rockwool InsulationView in gallery

Rockwool insulation is a very useful material. There are many benefits to it, many that we will list right way. While there are other benefits not listed, these are the most common that everyone who uses rockwool experiences. 

Rockwool Insulation Factors

  • Sustainable – rockwool insulation is made with around 75% recycled materials. Yep. The rocks used are recycled and also recyclable. So is any paper covering the rockwool and protecting it from exposure.
  • Efficient – those who switch to rockwool insulation often report a lower energy bill. This is because rockwool insulation retains heat and slows the transfer of heat. So it works exceptionally well in both the winter and the summer.
  • Fire-resistant – rockwool insulation was heated to 3000-degrees when it was formed. But it can stand about half that without melting. This means it is very fire-resistant and there isn’t much that can get through it.
  • Water-resistant – not only can rockwool insulation resist water but it actually repels it. So this makes it perfect for areas with a lot of rain. Soaked insulation is usually no good, but rockwool does a wonderful job repelling water.
  • Soundproof – while not entirely soundproof, rockwool insulation does do a fairly good job of deafening sounds. So when used in walls and ceilings, it can reduce the sound transfer between the indoors and outdoors.
  • Doesn’t degrade – over time, many other insulations degrade and deteriorate, but since it is made of rocks, rockwool does not. After all, if you fill your walls with rocks, the rocks will be there during your entire lifetime. 
  • Mold-resistant – anything can grow mold if another material gets on it and allows it to stick. But alone, rockwool insulation does resist mold. It is very rare for mold to be found near rockwool insulation. 
  • Easy-to-install – rockwool insulation is easy to install. Unlike other insulations, it doesn’t require staples which can be both dangerous and such a hassle when you get one crooked or in the wrong place. 

Where To Put Rockwool Insulation

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Now you may be thinking about where you want to install rockwool insulation. You may want to replace old insulation with it and you may be building a new house and trying to decide which insulation to use.

The bottom line is that rockwool insulation can be installed anywhere fiberglass insulation can be installed. In short, it can be used anywhere that you’d have insulation installed. From ceilings to walls or even floors. 

Here’s a list of the most common places that rockwool insulation is installed: 

  • Ceilings
  • Attics
  • Crawlspaces
  • Walls
  • Floors/Basements 

Where Not To Put Rockwool Insulation 

So now you’re probably wondering where in the world rockwool insulation can’t be installed. The short answer is that there isn’t anywhere. Rockwool insulation can be installed anywhere. So why isn’t it? 

Well, we will go more into the details later when comparing it to other insulation but again, the short answer is that it is more expensive than other insulation. Is it worth it? That’s the question we need to address. 

Rockwool Insulation Vs. Other Insulation Types

Rockwool Insulation Vs. Other Insulation TypesView in gallery

When looking at the pros and cons of rockwool insulation, it’s usually best to start with comparing it to other products. After all, if they all have the same pro or the same con, it sort of makes that point inconsequential. 


When comparing the efficiency of different insulations, it’s usually best to look at the R-value. However, there are also other hidden ways that makes insulation work well regardless of R-value. In this case, rockwool comes out on top. 

For example, the R-value is how well-insulated the material is based on how thick it is. Some areas work well with a thin layer of foam while others need six or eight inches of a fluffier insulation.

  • Rockwool – 3-4 per inch, range of R13 to R38
  • Fiberglass – 2-3 per inch, range of R11 to R37
  • Cellulose – 3-4 per inch, range of R11 to R30
  • Foam – 3-5 per inch, range of R3 to R25
  • Natural Fibers – 1-3 per inch, range depends on the material 


When it comes to eco-friendliness, we start off by comparing how much of the product is made with recyclable materials. Of course, natural materials are more recyclable but we’re talking about recycling to make the insulation. 

  • Rockwool – 70-75% recycled 
  • Fiberglass – 20-40% recycled 
  • Cellulose – 80-90% recycled 
  • Foam – depends on brand
  • Natural Fibers – usually 100% recycled 
  • Bonus: denim – 100% recycled 


Cost is a huge factor for most people so it cannot be neglected. For this example and comparison, we’re going to list the cost of each per square foot as this is how many different types of insulation are sold. 

As you can see, there are many options available and a large range for a few options. However, when it comes to rockwool, the range is much smaller because there aren’t any cheap options for rockwool insulation. 

  • Rockwool – average $1.50 to $2 per square foot
  • Fiberglass – average $0.50 to $1 per square foot
  • Cellulose – average $1 per square foot
  • Foam – fair range of $0.30 to $2 per square foot
  • Natural Fibers – large range of $0.50 to $3 per square foot


Fire resistance matters a lot. After all, some insulations can catch on fire quickly, becoming a huge safety hazard. It is hard to grade a type of insulation and give it a “fire rating” unless you are the fire department.

So today, we’re going to go with listing the temperature that each insulation can withstand without melting or catching on fire. 

  • Rockwool – 1,500 degrees Fahrenheit 
  • Fiberglass – 1,000 degrees Fahrenheit 
  • Cellulose – 800 degrees Fahrenheit  
  • Foam – 700 degrees Fahrenheit 
  • Natural Fibers – depends on the material 


Water-resistant materials are more efficient in every way. That’s why it is important to make sure your insulation is water-resistant. Let’s take a look at just how water-resistant different types of insulation are. 

Every insulation can be water-resistant, but when it comes to waterproofing them, things get more complicated. Here’s a quick rundown of what that means for your insulation. 

  • Rockwool – yes, fully 
  • Fiberglass – yes, only after resin application 
  • Cellulose – yes, after protectant is applied 
  • Foam – high-density, closed-cell only 
  • Natural Fibers – sometimes 


Versatility is important because this means different thicknesses, sizes, and installation options. The more popular an insulation is, the more options you will have. So let’s take a look at the popularity of different insulations.

In this case, the actual number for any other insulation is hard to calculate because fiberglass takes up more than 70% of the space. However, because there are many ways to use foam, it comes in at a close second as far as versatility is concerned. 

How To Install Rockwool Insulation 

How To Install Rockwool Insulation View in gallery

Installing each type of insulation is very unique. The process varies greatly between them. For example, spray foam requires a special sprayer while fiberglass requires staples. Here’s how to install rockwool. 

Step 1: Fill Gaps With Foam/Caulk

Before you start installing any insulation, it’s a good idea to fill any gaps that you find in the area you will be installing it. Start with caulk around windows and doors and anywhere that is less than half an inch or so wide.

Then switch to expanding foam for larger cracks and gaps. This will help insulate. After all, the insulation shouldn’t be filling gaps but cushioning the area between the indoors and the outdoors, so rely on expanding foam for this. 

Step 2: Don Gear

Now, there’s something you should know about rockwool insulation. Although it doesn’t make your skin or throat itch like fiberglass insulation does, it can still be quite dangerous to inhale openly. 

So always wear a mask and preferably goggles whenever you are installing rockwool insulation. This is important so it’s best not to rush yourself and skip it. Your future and your lungs will thank you.

Step 3: Install In Floors And Walls

Start from the bottom and outside of the house and begin installing the insulation. Make sure you have your mask on. The exterior walls, crawlspaces, and basement ceilings. Cut each piece one at a time and install it.

You shouldn’t need to add any staples or anything. All you need to do is add it into the hole as if adding a piece to the puzzle. Cut around any obstructions such as outlet boxes with a utility knife.

Step 4: Install In Ceilings And Attic 

After you install it in the walls, then you are ready to install the insulation in the ceilings and attic, if you have one. It should work the same and should fit snugly in the slots without falling out, even if you don’t add any ceiling covering. 

If it doesn’t fit, feel free to add a few horizontal boards to help keep it in. Install them before you put the insulation in so that it won’t keep falling on you as you screw in the new support boards. 

Enjoy Your New Rockwool Insulation

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If you’re switching to rockwool insulation, chances are that you are making a great choice for your family! Rockwool insulation is efficient in just about every way. It works so well and is environmentally friendly.

So you can feel good about this choice. If you can take the price then you shouldn’t think twice about switching to rockwool insulation. You’ve learned what you need to know and you’re ready to take that step.