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How to Insulate Walls

Are you afraid your house might burn to the ground?

It scares the bejesus out of me, especially since we have kids.

Of course we take all the precautions: smoke detectors, GFCIs, fire extinguisher, trained guinea pigs….

Yah, did you know you can train guinea pigs to squeak when they smell smoke?

Just kidding but that would be really cool.

If you want an ironclad way to save energy and make your house more fire resistant check out Roxul insulation.

I’ve wanted to use it for years and finally got the opportunity this past weekend. And of course I’m going to share my experience with you.

Plus, there are not 1 but 3 videos you need to watch that prove how awesome Roxul is for DIYers like you and me 🙂

What’s Roxul (Now Rockwool!)

A lot of shows on HGTV show contractors using Roxul. So I decided to research it and found out why they love it so much.


Roxul is made from stone fibers. As a result, it can withstand 2000F temperatures without burning.

That’s pretty hot!!!

I’m not saying Roxul with prevent your home from catching on fire. But it gives you extra time to escape a bad situation.

When I forked over $300 for 6 bags I knew it was money well spent.

Plus, Roxul has soundproofing qualities that help keep homes a bit more quiet.

This is super important for me since I get up at 4:25 am every weekday. Let’s just say my kids don’t share my enthusiasm for early mornings, haha.

Roxul is totally a DIY project.

Here are all the supplies you need

  • Long Sleeve Shirt
  • Gloves
  • Respirator
  • Drywall Knife or Bread Knife
  • Measuring Tape
  • Roxul Insulation (I used R15 ComfortBatt)

Here’s what you’ll learn

  • How to insulate walls with Roxul

I can’t wait to show you the videos, so here we go.

Using Rockwool to Insulate Walls

If you can cut a loaf of bread you can use Roxul.

You’ll see why a bit later on.

Roxul fits into standard stud bays that are 16 inches on center. Each batt is

  • 3 1/2 inches thick (standard stud bay depth)
  • 15 1/4 inches wide (standard stud bay width)
  • 47 inches long
  • fire and water resistant

One bag has 12 batts and covers 59.7 square feet.

I needed about 6 bags to insulate a 12 x 12 bathroom (7 foot ceilings) and 10 x 5 closet. Hence the 6 bags for $300.

The bags were $47 each at Lowe’s. Other kinds of insulation were about the same price.

Oh that’s the other thing, you shouldn’t have to visit any specialty store to buy Roxul. It’s carried at most local box stores.

Start the installation by butting a batt flush with the stud header, aka top wood piece in stud bay.

Butt roxul to top of stud bay

Measure the distance between the bottom of the top batt and the bottom of the stud bay.

I cut off about 2 inches of Roxul using a drywall or bread knife.

Trim Roxul

Cutting Roxul is literally as easy as cutting through a loaf of Italian bread. But it doesn’t taste nearly as good (just kidding, please don’t try eating Roxul).

When you push the Roxul into the stud bay don’t compress it. It should be fluffy and flush with the wood studs. This helps the Roxul retain it’s energy efficiency.

Make roxul flush with studs

When you cut Roxul make the new piece 1/2 to 1 inch wider or longer than you need. This allows the Roxul to fit nice and tight.

What do you do if you’ve got pipes, wires, or electrical boxes?

How to Use Rockwool Around Pipes and Wires

Not all stud bays are empty.

Some bays will have pipes, wires, and electrical boxes to work around.

No problem.

You can cut out a portion of the Roxul and slide it around vent or waste pipes. Check out my video for specific instructions.

Slide Roxul around pipes

Here’s a little tip, add the Roxul to the middle of the stud bay to work around a pipe because the pipe will have some flexibility.

This makes it way easier to push the Roxul behind the pipe.

If you’ve got wires that run horizontally across stud bays just cut a slit in the Roxul. The wires can fit snuggly in that slit within the Roxul.

And if you’ve got an electrical box cut out a portion of the Roxul. It’s okay for the Roxul to fit snug around the box, after all, this is where many drafts come from.

Check out my video to see how easy it is to work with Roxul – just one reason among many why I shelled out the dinero for it!!

What’s Next

Roxul changed it’s name to Rockwool after we made this tutorial. It’s still our #1 insulation and we use it to insulate old homes.

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.

Thanks as always for reading, watching, and being part of our awesome community.



Roxul Insulation for Bathrooms