Rockwool Insulation

By Todd Fratzel on Insulation

Stone Wool Insulation Commonly Known as Rock Wool

Quite a few readers have been asking questions about rock wool type insulation so I thought it was a topic worth discussing. If you’re not familiar with the term rock wool insulation, sometimes called mineral/stone wool insulation is fire resistant insulation product. In addition most stone wool insulation products are also water and moisture resistant, excellent sound barrier properties and easy to install.

Excellent Fire Resistant Properties

As you can see in the photo rock wool type insulation have excellent fire resistant properties. Roxul brand insulation (shown) has a melting point of 2,150°F. Obviously this gives it a huge advantage over insulation products like foam, fiberglass and cellulose which are all flammable at much lower temperatures.

The fire resistant properties are so good that this type of product is often used for fire blocking applications, insulating around chimneys and fireplaces and situations where the insulation needs to be left exposed. Obviously these type of special applications must be approved by the location building code official and meet the requirements of your local building code.

Excellent Water & Moisture Resistant Properties

Rock wool insulation also has excellent water and moisture resistant properties. For example Roxul insulation will not absorb water and does not rot, promote mildew, fungi, or bacteria, or sustain vermin. When you consider the devastating effects of mold damage in some of today’s modern homes it’s a wonder more people don’t insulate with this product!

Dimensionally Stable

One of the characteristics of this insulation that I really like is how dimensionally stable it is. Rock wool insulation products maintain their shape really well. Unlike fiberglass insulation that is easily compressed and unlike cellulose that settles over time rock wood insulation will hold it’s shape. This is extremely important in situations where a snug fit is all that keeps the insulation in place.

My Favorite Use

Over the years I’ve used rock wool insulation on almost every building project. It’s not a product that we’ve used in large quantities but it is a product that can be extremely useful. One of the most common applications that I use it for is insulating around fire place inserts. Today more and more people are installing gas fireplace inserts in new home designs.

The bummer about inserts is all the clearances you need to combustible materials. If you maintain those clearances with products like fiberglass and cellulose then you end up have a large area of you home without any wall insulation. Obviously that’s something we want to avoid especially with the cost of fuel these days.

So we use rock wool insulation to insulate the area of the clearance zone. This allows us to maintain the fireplace clearances while maintaining the building’s insulation barrier.

About the author

Todd Fratzel

I'm full time builder for a large construction company in New Hampshire. I run their design-build division that specializes in custom homes, commercial design-build projects and sub-divisions. I'm also a licensed civil and structural engineer with extensive experience in civil and structural design and home construction. My hope is that I can share my experience in the home construction, home improvement and home renovation profession with other builders and home owners. I'm also the Editor-in-Chief and Founder of Tool Box Buzz. Please feel free to contact me if you have any questions, suggestions or you'd like to inquire about advertising on this site.

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  1. chris says:

    What is the cost compared to other insulation? And, is it hard to find an installer?

    • Todd says:

      The cost varies depending on the size you want. Cost can be similar to fiberglass up to 20% more. Most all insulation contractors have access to it.

  2. jeff_williams says:

    Have a link or additional info for rockwool around fireplaces? I’m at that point in my install currently and would love to see some more info so I don’t burn my place down in the future.

  3. Darell says:

    Is this what they also use for sound barrier between floors (basement and main floor).

  4. Bob says:

    It is the best and easist insulation to use for a DIYer! Use an electric carving knife, works great!
    It costs more than fiberglass but is way easier to install. Unbeliveable sound deadining!
    Great Stuff foamed all framing (100 cans – $ 600) and then used Roxul R-23 brand rock wool!
    Inspector said “best insulation job I have ever seen” , ” this is the first residential application I have ever seen” , Rock wool is not the norm around here (Tahoe), I had to special order from Lowes. I still used kraft faced R-38 fiberglass in the cathedral ceiling.

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