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Roxul Insulation (lower utility BILLS)

Roxul insulation was my #1 choice for our master bathroom remodel. I’ll explain why.

It’s made of Basalt rock and recycled slag. If you don’t know, slag is a by-product of steel production. I live in Pittsburgh, so it’s kinda second nature to know about slag.

Little side note: I was a geology major in college for about 1 year…then switched to chemistry. So I geek out on cool things that make your home a better place to live.

Today you’ll see why I chose Roxul for our wonky 100 year old bathroom remodel.

Plus I’ve got a surprise at the end of my video. Who doesn’t love good surprises?

What is Mineral Wool

Why is mineral wool so awesome?

Reason one: Roxul won’t catch on fire until about 2000F. I don’t know about you, I want a chance to run if my house catches fire.

Reason two: Roxul is inorganic and therefore not a food source for mold. Mold in a house is BAD, unless it’s in the form of blue cheese.

Reason three:  it’s water repellent. If Roxul gets damp it won’t lose it’s R-rating, meaning it won’t lose it’s ability to insulate.

Cool stuff.

Here are the supplies you need to install Roxul

Roxul is especially helpful in old homes that don’t have normal stud bays!!! You’ll see what I’m talking about.

Roxul Insulation…important concepts to remember

Whatever insulation you use, wear protective gear.

The little fibers are not good for your body. Plus it gets itchy and nobody likes being itchy. Remember Chickenpox?

Roxul ComfortBatt can be used for exterior walls, basements, and crawlspaces.

Roxul for exterior walls

ComfortBatt is R-15 rated and should be used in 16″ on center stud walls

R-15 Rated

How much Roxul should you buy?

It’s simple. Measure the dimensions of your wall, length x width, and get your square footage.

Obviously you don’t need to be a genius. But deduct for doors and windows.

I like to buy more than I need then take back what isn’t used. Each Roxul bag covers 59.7 square feet.

Roxul Square Footage

I feel like this is super important to keep in mind. So I’m repeating myself…the reason I love Roxul is because it’s fire resistant and water repellent.

Not every insulation out there can say this.

Roxul is fire repellent

In my video I mention that we’ll be using Schluter KERDI-BOARD to waterproof the shower surround. It’s an awesome waterproofing material. But no matter what waterproofing you use, you’re still going to get water vapor in the stud bay.

The fact that Roxul won’t lose it’s R-Value because it’s water repellent means it’s a great option for bathrooms.

After all, if insulation loses it’s R-Value your bathroom won’t be well insulated and your utility bills will go up.


How to Install Roxul Insulation…it’s like cutting bread

Hopefully if you remodel your bathroom it’s a bit easier than my project. This situation is strange because the bathroom is over 100 years old and the framing is a bit wonky to say the least.

Fortunately the exterior wall had framing that’s 16 inches on-center. No matter what your situation you’ll have to cut insulation to size, unless of course you’re using blown-in insulation…which is messy.

I like starting at the top of the stud bay and placing Roxul flush with the header.

Start at the top

Roxul should sit flush with adjacent batts and studs, there shouldn’t be any gap.

There should be no gaps
No gap near studs

Roxul is super easy to cut. Seriously, it’s easier than cutting bread. Use either a utility knife or drywall saw to cut it. A drywall T-square will help you make clean, straight cuts.

Cutting Roxul is easy

You can slice or groove out the Roxul and fish electrical lines or pipes into it.

Slice Roxul for electrical or pipes

Like I said, this house has strange framing…but that’s not a problem. You can cut Roxul to any size you need. For example, this little cheese slice.

Cutting weird pieces of Roxul
It's a Roxul Cheese Slice

Windows are one of the worst culprits when it comes to losing heat or cool air. Roxul made it easy to insulate around our new window and make this bathroom even more energy efficient for our tenants.

Add Roxul around windows

Remember how I said Roxul is fire resistant. I decided to try and light it on fire.

Roxul won't light on fire!!

I was unsuccessful. Which was cool…don’t try this at home!!

Watch my video for the complete step-by-step Roxul installation instructions.

What’s Next

Many thanks to Rockwool for sponsoring today’s video.

We installed KERDI-BOARD in the shower area to add additional R-Value to the bathroom. This was also a very straight forward project.

If you’re doing a bathroom remodel and need help, join one of our online courses – they’ll make your bathroom renovation much easier!

Let me know if you have any questions and I’ll do my best to help.



Roxul Insulation